1 acs 168 structured programming using the computer spring 2002 by joaquin vila prepared by shirley...
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1
ACS 168Structured Programming Using
the Computer
Spring 2002
By
Joaquin Vila
Prepared by
Shirley White
2
Reminders
Keep Reading Chapter 3 Self-Test exercises Supplemental Instruction (Exam Review) Any question about chapter 2? Homework Assignment (Montecarlo Simulation) Quiz
3
QUIZ
4
Practice
Write an if statement to compute and print the total for a sale. The cost of the items being purchased is stored in sub_total, a variable of type double. A variable customer_type, of type char, has the value ‘N’ for normal or ‘G’ for government. Customers of type ‘G’ do not pay sales tax. The sales tax rate is stored in a constant named tax_rate.
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Practice
Design and write a program that will prompt for, receive, and total a collection of payroll amounts entered by the user until a sentinel amount of -99 is entered. After the sentinel has been entered, display the total payroll amount on the screen.
6
Practice
Write a while loop to compute the sum of all integers between first and second (including first and second), where first and second are integers and first <= second. You may not change the value of either first or second.
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Practice
Write a program that sums a sequence of integers. Assume that the first integer read specifies the number of values remaining to be entered. Your program should read only one value at a time. A typical input sequence might be
5 100 200 300 400 500
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Practice
Write a program that finds the smallest of several integers. Assume that input will end when a sentinel value of –999 is read. Do not count –999 as one of the integers to consider.
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Display 2.14 Charge Card Program (1 of 2)
#include <iostream>
using namespace std;
int main( )
{
double balance = 50.00;
int count = 0;
cout << "This program tells you how long it takes\n"
<< "to accumulate a debt of $100, starting with\n"
<< "an initial balance of $50 owed.\n"
<< "The interest rate is 2% per month.\n";
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Display 2.14 Charge Card Program (2 of 2)
while (balance < 100.00) { balance = balance + 0.02 * balance;
count++; }
cout << "After " << count << " months,\n";
cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
cout << "your balance due will be $" << balance << endl;
return 0;
}
count++ accomplishes the same thing as
count = count +1
count++ accomplishes the same thing as
count = count +1
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Naming Constants
Do not hard-code numbers into your program that are likely to change.
Example: If the tax rate is 4% (0.04) today, it will go up. Make such
numbers declared constants unless you want to hunt through your code to find and replace all instances of 0.04 and try to decide if it is a tax rate, then replace it by the new tax rate, 0.05.
Name declared constants with the const keyword.Spell declared constant names with upper case letters,with successive words separated by underscores.Example:
const int BRANCH_COUNT = 10;const double TAX_RATE = 0.04;
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Summary (1 of 2)
Use meaningful names for variables. Check that variables have been declared before use,
and have the correct data type. Be sure variables has a value before use. This can be
done by initialization at definition, or by assigning a value before first use.
Use enough parentheses to make the order of operations clear. Remember, code is meant to be read, which implies writing for an audience.
Always have your program prompt the user for expected input. Always echo user’s input.
An if-else statement chooses between two blocks of code to execute. An if statement chooses whether to execute a block of code.
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Summary (2 of 2)
A do-while always executes its body at least once. A while loop may not execute its body at all.
Numeric constants should be given meaningful names to be used instead of the numbers. Use the const modifier to do this.
Use indenting, spacing, and line break patterns similar to the sample code to group sections of code such as the body of a while statement, or the affirmative and negative clauses of an if-else statement.
Insert commentary to explain major subsections of your code, or to explain any unclear part of your program.
Make your code clear. Remember, a program is meant to be read by programmers, not just compilers.
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Chapter 3Procedural Abstraction & Functions That Return a Value
3.1 Top Down DesignStep wise refinement, also known as
divide and conquer, means dividing the problem into subproblems such that once each has been solved, the big problem is solved.
The subproblems should be smaller and easier to understand and to solve than the big problem.
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3.2 Predefined Functions: Libraries
C++ comes with libraries of predefined functions.
How do we use predefined (or library) functions?
Everything must be declared before it is used. The statement #include <file> brings the declarations of library functions into your program, so you can use the library functions.
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Libraries
#include <cmath> // include declarations of math
// library functions
#include <iostream> // include definitions of
// iostream objects
using namespace std; // make names available
int main()
{
cout << sqrt(3.0) << endl; // call math library function
} // sqrt with argument 3.0, send
// the returned value to cout
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3.2 Function Call
A function call is an expression consisting of a function name followed by arguments enclosed in parentheses. Multiple arguments are separated by commas.
Syntax:
FunctionName(Arg_List)
where Arg_List is a comma separated list of arguments.
Examples:– side = sqrt(area);– cout <<“2.5 to the power 3.0 is “
<< pow(2.5, 3.0);
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Display 3.1 A Function Call (pt 1)
//Computes the size of a dog house that can be purchased//given the user’s budget.#include <iostream>#include <cmath>using namespace std;
int main( ){ const double COST_PER_SQ_FT = 10.50; double budget, area, length_side;
cout << "Enter the amount budgeted for your dog house $"; cin >> budget;
area = budget/COST_PER_SQ_FT; length_side = sqrt(area); // the function call
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Display 3.1 A Function call (pt 2)
cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precision(2); cout << "For a price of $" << budget << endl << "I can build you a luxurious square dog
house\n" << "that is " << length_side << " feet on each side.\n";
return 0;}
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PITFALL:Problems with Library functions
Some compilers do not comply with the ISO Standard.
If your compiler does not work with
#include <iostream>
use
#include <iostream.h> Similarly, for headers like cstdlib: use stdlib.h, and
for cmath, use math.h Most compilers at least coexist with the headers
without the .h, but some are hostile to these headers.
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Type changing functions
Question: 9/2 is an int, but we want the 4.5 floating point result. We want the integer part of some floating point number. How do we manage?
Answer: Type casting, or “type changing functions”.
C++ provides a function named double that takes a
value of some other type and converts it to double.
Example:
int total, number;
double ratio;
// input total, number
winnings = double(total) / number;
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PITFALL: Integer division drops the fractional part
REMEMBER: integer division returns just the quotient. The remainder (and any fractional part) are dropped.
If the numerator and denominator are both integer values, the division is done as integer arithmetic, dropping the fractional part.
Example: 11 / 2 is 5, NOT 5.5
10 / 3 is 3, NOT 3.333
Even if assigned to a double variable:double ratio = 10/3; // assigned value is 3, NOT 3.3
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3.3 Programmer Defined Functions
You can define your own functions. You can put your functions in the same file
as the main function or in a separate file. If you put your function after the function
containing a call to your function, or in a separate file, you must put a prototype (defined in the next slide) for your function some place in the file where it is called, prior to the call.
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Function Prototypes A function prototype tells you all the information you need to
call the function. A prototype of a function (or its definition) must appear in your code prior to any call to the function.
Syntax: Don’t forget the semicolon– Type_of_returned_value Function_Name(Parameter_list);– Write prototype comments for each function.– Parameter_list is a comma separated list of parameter
definitions:
type_1 param_1, type_2 param_2, …. type_N param_N
Example:
double total_weight(int number, double weight_of_one);
// Returns total weight of number of items that
// each weigh weight_of_one
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A function is like a small program
To understand functions, keep these points in mind:
A function definition is like a small program and calling the function is the same thing as running this small “program.”
A function has formal parameters, rather than cin, for input. The arguments for the function are input and they are plugged in for the formal parameters.
A function of the kind discussed in this chapter does not send any output to the screen, but does send a kind of “output” back to the program. The function returns a return-statement instead of cout-statement for “output.”
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Display 3.3 A function Definition (Slide 1 of 2)
#include <iostream>
using namespace std;
double total_cost(int number_par, double price_par);
//Computes the total cost, including 5% sales tax,
//on number_par items at a cost of price_par each.
int main( )
{
double price, bill;
int number;
cout << "Enter the number of items purchased: ";
cin >> number;
cout << "Enter the price per item $";
cin >> price;
bill = total_cost(number, price); The function call cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
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Display 3.3 A function Definition (Slide 2)
cout << number << " items at " << "$" << price << " each.\n" << "Final bill, including tax, is $" << bill << endl; return 0;}
double total_cost(int number_par, double price_par){ const double TAX_RATE = 0.05; //5% sales tax double subtotal; subtotal = price_par * number_par; return (subtotal + subtotal*TAX_RATE);}
This line is the function heading.This line is the function heading.The function body is the part between the { }.
The function body is the part between the { }.
The entire function is called the function definition.
The entire function is called the function definition.
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Call-by-value Parameters
Consider the function call:bill = total_cost(number, price);
The values of the arguments number and price are “plugged” in for the formal parameters . This process is (A precise definition of what “plugged” means will be presented later. For now, we will use this simile.)
A function of the kind discussed in this chapter does not send any output to the screen, but does send a kind of “output” back to the program. The function returns a return-statement instead of cout-statement for “output.”
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Alternate form for Function Prototypes
The parameter names are not required:
double total_cost(int number, double price); It is permissible to write:
double total_cost(int, double ); Nevertheless, code should be readable to
programmers as well as understandable by the compiler, so check for readability and chose to use parameter names when it increases readability.
Function HEADERS (in the definition) must use parameter names. (There is an exception to this rule that we will not deal with in this course.)
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Anatomy of a Function Call (part 1 of 3)
#include <iostream>
using namespace std;
double total_cost(int number_par, double price_par);
//Computes the total cost, including 5% sales tax,
//on number_par items at a cost of price_par each.
int main( )
{
double price, bill;
int number;
cout << "Enter the number of items purchased: ";
cin >> number;
cout << "Enter the price per item $";
cin >> price;
bill = total_cost(number, price); The function call cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
Before the function is called, the value of the variables number and price are set to 2 and 10.10, by cin.
Before the function is called, the value of the variables number and price are set to 2 and 10.10, by cin.
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Anatomy of a Function Call (part 2 of 3)
double total_cost(int number_par, double price_par){ const double TAX_RATE = 0.05; //5% sales tax
double subtotal;
subtotal = price_par * number_par;
return (subtotal + subtotal*TAX_RATE);
}
The value of number (which is 2) is plugged in for number_par and the value of price (which is 10.10) is plugged for price_par:
The value of number (which is 2) is plugged in for number_par and the value of price (which is 10.10) is plugged for price_par:
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Anatomy of a Function Call (part 3 of 3)
The execution produces the following effect:
double total_cost(int 2, double 10.10){ const double TAX_RATE = 0.05; //5% sales tax
double subtotal;
subtotal = 10.10 * 2;
return (subtotal + subtotal*TAX_RATE);
}
The body of the function is executed, i.e., the following is executed:
The body of the function is executed, i.e., the following is executed:
When the return statement is executed, the value of the expression after the return is the value returned by the function. In this case, whenreturn (subtotal + subtotal*TAX_RATE); is executed, the value of (subtotal + subtotal*TAX_RATE), is returned by the function call which wasbill = total_cost(number, price); the value of bill is set to 21.21
When the return statement is executed, the value of the expression after the return is the value returned by the function. In this case, whenreturn (subtotal + subtotal*TAX_RATE); is executed, the value of (subtotal + subtotal*TAX_RATE), is returned by the function call which wasbill = total_cost(number, price); the value of bill is set to 21.21
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PITFALL
Arguments in the wrong order
When a function is called, C++ substitutes the first argument given in the call for the first parameter in the definition, the second argument for the second parameter, and so on.
There is no check for reasonableness. The only things checked are: i) that there is agreement of argument type with parameter type and ii) that the number of arguments agrees with the number of parameters.
If you do not put correct arguments in call in the correct order, C++ will happily assign the “wrong” arguments to the “right” parameters.
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Summary of Syntax for a Function that Returns a Value
Function Prototype:
Type_Returned Function_Name(Parameter_List);
Prototype Comment function headerFunction DefinitionsType_Returned Function_Name(Parameter_List)
{ Declaration_1 Declaration_2 . . . Must include one or Declaration_Last; more return statements.
body Executable_1; Executable_2; . . . Executable_Last
}
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Principle of Information Hiding
David Parnas, in 1972 stated the principle of information hiding.
– A function’s author (programmer) should know everything about how the function does its job, but nothing but specifications about how the function will be used.
– The client programmer -- the programmer who will call the function in her code -- should know only the function specifications, but nothing about how the function is implemented.
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The Black Box Analogy
Based on the Principle of Information Hiding, the text describes the BLACK BOX analogy.
When using a function, we behave as if we know nothing about how the function does its job, that we know only the specifications for the function.
When writing a function, we behave as if we know nothing but the specifications about how the function is to be used.
In this way, we avoid writing either application code that depends on the internals of the function or writing function code that depends in some way on the internal structure of the application.
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3.4 Procedural AbstractionWhen applied to a function definition, the principle of procedural
abstraction means that your function should be written so that it can be used like a black box. This means the user of a function should not need to look at the internals of the function to see how the function works. The function prototype and accompanying commentary should provide enough information for the programmer to use the function.
To ensure that your function definitions have this property, you should adhere to these rules:
– The prototype comment should tell the programmer any and all conditions that are required of the arguments to the function and should describe the value returned by the function.
– All variables used in the function body should be declared in the function body. (The formal parameters are already declared in the function header.)
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3.5 Local Variables
Variables declared within the body of a function definition are said to be local to that function, or have that function’s block as their scope.
Variables declared within the body of the main function are said to be local to the main function, or to have that function’s block as their scope.
When we say a function is a local variable without further mention of a function, we mean that variable is local to some function definition.
If a variable is local to a function, you can have another variable with the same name that is local to either main or some other function.
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Global Constants and Variables
A named constant declared outside the body of any function definition is said to be a global named constant. A global named constant can be used in any function definition that follows the constant declaration. There is an exception to this we will point out later.
Variables declared outside the body any function is said to be global variables or to have global scope. Such a variable can be used in any function definition that follows the constant declaration. There is also an exception to this we will point out later.
Use of global variables ties functions that use the global variables in a way that makes understanding the functions individually nearly impossible. There is seldom any reason to use global variables.
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Display 3.11 Global Named Constants (Part 1 of 2)
//Computes the area of a circle and the volume of a sphere.//Uses the same radius for both calculations.#include <iostream>#include <cmath>
using namespace std;const double PI = 3.14159;
double area(double radius);//Returns the area of a circle with the specified radius.
double volume(double radius);//Returns the volume of a sphere with the specified radius.
int main( ){ double radius_of_both, area_of_circle, volume_of_sphere;
cout << "Enter a radius to use for both a circle\n" << "and a sphere (in inches): "; cin >> radius_of_both;
Here PI is a global constant that is visible to all parts of the program.
Here PI is a global constant that is visible to all parts of the program.
Where radius_of_both, area_of_circle, and volumn_of_sphere are all variables local to main and not visible to other modules unless passed in a function call.
Where radius_of_both, area_of_circle, and volumn_of_sphere are all variables local to main and not visible to other modules unless passed in a function call.
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Display 3.11 Global Named Constants (Part 2 of 2)
area_of_circle = area(radius_of_both); volume_of_sphere = volume(radius_of_both);
cout << "Radius = " << radius_of_both << " inches\n" << "Area of circle = " << area_of_circle << " square inches\n" << "Volume of sphere = " << volume_of_sphere << " cubic inches\n";
return 0;}
double area(double radius){ return (PI * pow(radius, 2));
}
double vo lume(double radius){ return ((4.0/3.0) * PI * pow(radius, 3));}
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Call-by-value Formal Parameters are Local Variables Formal
Parameter Used as Local Variable (Part 1 of 2)
//Law office billing program.#include <iostream>using namespace std;
const double RATE = 150.00; //Dollars per quarter hour.
double fee(int hours_worked, int minutes_worked);//Returns the charges for hours_worked hours and//minutes_worked minutes of legal services.
int main( ){ int hours, minutes; double bill;
cout << "Welcome to the offices of\n" << "Dewey, Cheatham, and Howe.\n" << "The law office with a heart.\n" << "Enter the hours and minutes" << " of your consultation:\n";
cin >> hours >> minutes;
Formal parameters are actually local variables that are initialized by the call mechanism to the value of the argument. They may be used in any way that a local variable can be used.
Formal parameters are actually local variables that are initialized by the call mechanism to the value of the argument. They may be used in any way that a local variable can be used.
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Formal Parameter Used as Local Variable (Part 2 of 2)
bill = fee(hours, minutes); The value of minutes is not changed by a call to fee. cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precision(2); cout << "For " << hours << " hours and " << minutes << " minutes, your bill is $" << bill << endl;
return 0;
} minutes_worked is a local variable
initialized to the value of minutes
double fee(int hours_worked, int minutes_worked) { int quarter_hours;
minutes_worked = hours_worked*60 + minutes_worked; quarter_hours = minutes_worked/15; return (quarter_hours*RATE);
}
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Namespaces Revisited (1 of 2)
All our use of namespaces has amounted to
#include <iostream>using namespace std;
While this is correct, we are sidestepping the reason namespaces were introduced into C++, though we have done this for good teaching reasons.
In short, we have been “polluting the global namespace.”
As long as our programs are small, this is not a problem.
This won’t always be the case, so you should learn to put the using directive in the proper place.
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Namespaces Revisited (2 of 2)
Placing a using directive anywhere is analogous to putting all the definitions from the namespace there. This is why we have been polluting the global namespace. We have been putting all the namespace std names from our header file in the global namespace.
The rule, then is:
Place the namespace directive,
using namespace std;
inside the block where the names will be used. The next slide is Display 3.13 with the namespace directive place correctly.
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Display 3.13 Using Namespaces (1 of 2)
//Computes the area of a circle and the volume of a sphere.//Uses the same radius for both calculations.#include <iostream>#include <cmath>//Some compilers may use math.h instead of cmath.
const double PI = 3.14159;
double area(double radius);//Returns the area of a circle with the specified radius.
double volume(double radius);//Returns the volume of a sphere with the specified radius.
int main( ){ using namespace std;
double radius_of_both, area_of_circle, volume_of_sphere;
cout << "Enter a radius to use for both a circle\n" << "and a sphere (in inches): "; cin >> radius_of_both;
Not here …
but here
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Display 3.13 Using Namespaces (1 of 2)
area_of_circle = area(radius_of_both); volume_of_sphere = volume(radius_of_both);
cout << "Radius = " << radius_of_both << " inches\n" << "Area of circle = " << area_of_circle << " square inches\n" << "Volume of sphere = " << volume_of_sphere << " cubic inches\n";
return 0;}double area(double radius) The behavior of this program is exactly{ the same as that of Display 3.11 using namespace std; return (PI * pow(radius, 2));}
double volume(double radius) { using namespace std; return ((4.0/3.0) * PI * pow(radius, 3));}
repeated here and here
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3.6 Overloading Function Names
C++ distinguishes two functions by examining the function name and the argument list for number and type of arguments.
The function that is chosen is the function with the same number of parameters as the number of arguments and and that matches the types of the parameter list sufficiently well.
This means you do not have to generate names for functions that have very much the same task, but have different types.
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Display 3.15 Overloading a Function Name (1 of 2)
//Illustrates overloading the function name ave.#include <iostream>
double ave(double n1, double n2);//Returns the average of the two numbers n1 and n2.
double ave(double n1, double n2, double n3);//Returns the average of the three numbers n1, n2, and n3.
int main( ){ using namespace std; cout << "The average of 2.0, 2.5, and 3.0 is " << ave(2.0, 2.5, 3.0) << endl;
cout << "The average of 4.5 and 5.5 is " << ave(4.5, 5.5) << endl; return 0;
}
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Overloading a Function Name (2 of 2)
double ave(double n1, double n2) Both these functions have the { same name, but have parameter return ((n1 + n2)/2.0); lists that are have different } numbers of parameters.
double ave(double n1, double n2, double n3){ return ((n1 + n2 + n3)/3.0);}
The compiler will choose the function definition to use according to the number of parameters sent in the call.
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Automatic Type Conversion
We pointed out that when overloading function names, the C++ compiler compares the number and sequence of types of the arguments to the number and sequence of types for candidate functions.
In choosing which of several candidates for use when overloading function names, the compiler will choose an exact match if one is available.
An integral type will be promoted to a larger integral type if necessary to find a match. An integral type will be promoted to a floating point type if necessary to get a match.
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Display 3.16 Overloading a function name (1 of 4)
//Determines whether a round pizza or a rectangular pizza is the best buy.#include <iostream>
double unitprice(int diameter, double price);//Returns the price per square inch of a round pizza.//The formal parameter named diameter is the diameter of the pizza//in inches. The formal parameter named price is the price of the pizza.
double unitprice(int length, int width, double price);//Returns the price per square inch of a rectangular pizza
//with dimensions length by width inches.
//The formal parameter price is the price of the pizza.
int main( ){ using namespace std;
int diameter, length, width; double price_round, unit_price_round, price_rectangular, unitprice_rectangular;
Same names
Notice the difference in the number and types of parameters used.
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Overloading a function name (2 of 4)
cout << "Welcome to the Pizza Consumers Union.\n"; cout << "Enter the diameter in inches" << " of a round pizza: "; cin >> diameter; cout << "Enter the price of a round pizza: $"; cin >> price_round;
cout << "Enter length and width in inches\n" << "of a rectangular pizza: ";
cin >> length >> width;
cout << "Enter the price of a rectangular pizza: $";
cin >> price_rectangular;
unitprice_rectangular = unitprice(length, width, price_rectangular);
unit_price_round = unitprice(diameter, price_round);
cout.setf(ios::fixed); cout.setf(ios::showpoint); cout.precision(2);
This call will go to the function:
double unitprice(int diameter, double price)
{
const double PI - 3.14159;
double raduis, area;
radius = diameter/double(2);
area = PI * radius * radius;
return (price/area);
}
This call will go to the function:
double unitprice(int diameter, double price)
{
const double PI - 3.14159;
double raduis, area;
radius = diameter/double(2);
area = PI * radius * radius;
return (price/area);
}
unitprice(int length, int, width, double price)
{ double area = length * width;
return (price/area); }
unitprice(int length, int, width, double price)
{ double area = length * width;
return (price/area); }
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Overloading a function name (3 of 4)
cout << endl << "Round pizza: Diameter = " << diameter << " inches\n" << "Price = $" << price_round << " Per square inch = $" << unit_price_round << endl << "Rectangular pizza: length = " << length << " inches\n" << "Rectangular pizza: Width = " << width << " inches\n" << "Price = $" << price_rectangular << " Per square inch = $" << unitprice_rectangular << endl;
if (unit_price_round < unitprice_rectangular) cout << "The round one is the better buy.\n"; else cout << "The rectangular one is the better buy.\n"; cout << "Buon Appetito!\n";
return 0;}
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Chapter Summary( 1 of 2)
A good plan of attack on a problem is to decompose the problem into smaller, more accessible problems, the decompose these into still more manageable problems. This is known as Top-Down Design.
A function that returns value is like a small program. Arguments provide input and the return value provides the output.
When a subtask for a program takes some values as input and produces a single value as its only output, then that subtask can be implemented as a function.
A function should be defied so that it can be used as a black box. The program author should know no more than the specification of the client use, and the client author should know nothing more than the specification of the implementation of the function. This rule is the principle of procedural abstraction.
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Chapter Summary (2 of 2)
A variable that is defined in a function is said to be local to the function.
Global named constants are declared using the const modifier. Declarations of global named constants are normally placed at the start of a program after the include directives, before the function prototypes.
Call by value formal parameters (the only kind we have discussed so far) are local variables to the function. Occasionally a formal parameter may be useful as a local variable.
When two or more function definitions have the same name, this is called function name overloading. When you overload a name, the function definitions must have different numbers of formal parameters or formal parameters of different types.