CS 1430: Programming in C++

1

Test 2

Friday

Functions

Arrays

For Loops

• Understand Concepts and Rules

• Memorize Concepts and Rules

• Apply Concepts and Rules to Different Problems

2

3

C++ Functions

Why?

Modularity!

4

C++ Functions• Function Prototype int IndexOfMax(const float s[], int size);

• Function Definition int IndexOfMax(const float s[], int size) { int index = 0; for (int i = 1; i < size; i ++) if (s[i] > s[index]) index = i; return index; }

• Function Call index = IndexOfMax(Test2Scores, numStudents);

5

Function Type

The type of the value returned by a function

float sqrt(float x);int IndexOfMax(const float s[], int size);bool eof();char RomanChar(int romanDigitValue);StudentType GetStudent();void ReadAnswers(char answers[], int numQuestions);

RETURN Statement!Not Parameters!

6

Prog4 Required Function

//---------------------------------------------------// Finds and returns an index of the look-up-mass // in the Masses array. Since the Masses array is // ordered in ascending order by mass, this function // returns the index of the first mass in the masses // array such that lookUpMass is less than or equal // to masses[i]. // On the off chance that no such index can be found, // returns -1. // params: ( ? , ? , ? )//---------------------------------------------------int FindIndexOfMass(const int masses[], int lookUpMass, int size);

7

Prog4 Required Function

//---------------------------------------------------// Returns the largest value in the dim array; // size is how many items are in the dim array. // params: ( ? , ? )//---------------------------------------------------float FindLargestDimension(const int dim[], int size);

8

Prog4 Required Function

//---------------------------------------------------// Returns the girth of a parcel where girth is // calculated as twice the difference of the sum of // the elements in the dim array and the largest of // the dimensions. // params: ( ? , ? )//---------------------------------------------------float Girth( const int dim[], int size);

Function Parameters

• Need to pass data to the function

• May need more than one value out of the function

Not Return Statement!

• Parameters are local variables

• Parameters get values or addresses at function calls

9

Formal Parameters and Actual Parameters

• Formal Parameters

In function prototype and definition

Must specify type with/without &

[] for arrays with/without const

• Actual Parameters

In function call

No type, &, and no [] or const for arrays10

Passing Parameters

• Basic Data Types (char, int, float, string, bool)

Pass by Value (without & in prototype)

Pass by Reference (with & in prototype)

• Arrays (of any data type)

Always Pass by Reference (pointer!)

(Never &)

• (Structure and Class)11

Value Parameters and Reference Parameters

const float REG_HOURS = 40.0;const float OVER_TIME = 1.5;

int main(){ float hours, rate, gross;

GetInput(rate, hours);

gross = GrossPay(rate, hours);

// display result

return 0;}

float GrossPay(float payRate, float hours){ if (hours > REG_HOURS) payRate = (hours - REG_HOURS) * OVER_TIME * payRate + REG_HOURS * payRate; else payRate = hours * payRate; return payRate;}

main()

GetInput()

void GetInput(float& payRate, float& hoursWorked){ cout << "Enter pay rate: "; cin >> payRate; cout << "Enter hours: "; cin >> hoursWorked;

return;}

GrossPay()Passing parameters

12.5 50

Passing parameters

Addresses of rate and hours

Return control

With value

Return control

12

In, Out, InOut Parameters

The original value of the actual parameterThe value of the actual parameter before the function call

InThe function uses the original value of the actual parameter, but

does not change its value.

OutThe function does not use the original value of the actual

parameter, but changes its value.

InOutThe function uses the original value of the actual parameter,

and also changes its value.

13

Tracing FunctionsInput: 10.5 53

float GrossPay(float payRate, float hours)void GetInput(float& payRate, float& hoursWorked);

main() GetInput() GrossPay() hours rate gross payRate& hoursWorked& hours payRate ? ? ? ? ? ? ? Addr of Addr of rate hours 10.5 53.0 53.0 10.5 556.5 556.5

14

Arrays• Array Declaration

const int MAX_SIZE = 30;int size = 30;

int nums[30];// Valid?float ArrayA[MAX_SIZE]; // Valid?

float ArrayB[size]; // Valid?

• Memory allocation

• Array Element and Index

• Index starts with 0

• An array element is the same as a single variable

• For Loop on arrayfor (int i = 0; i < size; i ++) cin >> ArrayA[i];

15

Functions on Arrays• Always passing by reference

• No &

• Size is passed separately

• Const for IN parameter

void ReadAnswers(char answers[], int numQuestions);

void ProcessAnswer(const char keys[], const char answers[],

int numQuestion, int& correct, bool& pass);

• Function calls

No []• Passing arrays and passing array elements

average = ArrayAvg(Scores, count);

max = Largest(Scores[0], Scores[1], Scores[2]);

• Linear search

return value or index

16

For Loops

• Same as while loops

• Better on arrays

• Better on Count-Controlled loops

17

Nested For Loops

int result;

for (int i = 4; i < 6; i ++)

{

result = 1;

for (int j = i; j > 1; j --)

result *= j;

cout << “The result: “ << result;

}

18

Tracing

int i, j, result;

for (i = 4; i < 6; i ++)

{

result = 1;

for (j = i; j > 1; j --)

result *= j;

cout << “The result: ”

<< result;

}

Do it yourself now!

i j result

? ? ?

4

1

4

4

3

12

2

24

1

5

1

5

5

4

20

3

60

2

120

1

619

Schedule

• Quiz7-1

• Lab7 & Lab8

• Prog4

• Test 2

20

21

Test 1

Test 2

Test 3

FinalFinal