Simplest program and Data Output

Sen Zhang

The simplest program looks like a single person company!

void main(){

// this starts a comment line// here is where you put your code…

}

One function, with a head and the empty body

The simplest program looks like a single person company!

int main(){

// this starts a comment line// here is where you put your code…return 0;

}

One function, with a head and the empty body

Why main needs to return a value ?

• DOS command to determine the return code is ERRORLEVEL, most people use the name errorlevel.

• Errorlevels are not a standard feature of every command. A certain errorlevel may mean anything the programmer wanted it to. Most programmers agree that an errorlevel 0 means the command executed succesfully, and an errorlevel 1 or higher usually spells trouble. But there are many exceptions to this general rule.

• int main() {return 11.9;

• }• • c:\sen\t1222\Debug>echo %errorlevel%

0• c:\sen\t1222\Debug>t1222• c:\sen\t1222\Debug>echo %errorlevel%

11•

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The cout Object

• The cout object represents the standard output display device, so anything you insert into cout will reflect on the standard output display device.– The display device is usually a video screen– Name derived from Console OUTput and pronounced

“see out”

• Data is passed to cout by the insertion symbol cout << “Hello there, World!”;

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C++ Sample Code using cout

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Preprocessor Command

• Performs an action before the compiler translates source code to machine code– An example is: #include <iostream>– Causes the iostream file to be inserted wherever

the #include command appears

• iostream is part of the C++ standard library– Included in iostream are two important classes:• istream: Declarations and methods for data input• ostream: Declarations and methods for data output

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Namespaces

• Files accessed by compiler when looking for prewritten classes or functions

• Sample namespace statement:– using namespace std;– iostream contained in a namespace called std– Compiler uses iostream’s cout object from std whenever cout is referenced

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More C++ Sample Code

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More C++ Sample Code (continued)

#include <iostream>using namespace std;

int main(){cout<<"hi!";cout<<endl;cout<<3+5;cout<<endl;cout<<"3+5";return 0;}

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Formatted Output

• Read book, page 53 to 66• Besides displaying correct information, a

program must present results attractively.• Field width manipulators: control format of

numbers displayed by cout– Manipulators included in the output stream

Output manipulators

• Output manipulators are items used to manipulate how the output stream of characters is displayed.

Manipulators for columnizng styles

• setw(n)• setfill(‘c’)

• When a manipulator requiring an argument is used, the iomanip header file must be included as part of the program.

• This is accomplished by the preprocessor command #include <iomanip>.

Setw(width)

• The setw(width) manipulator included in the stream of data passed to cout is used to set the displayed field width.

• The width in this manipulator should be replaced by a concrete integer number say 10. It will reserves a field with a width of 10 for any subsequent number in the stream.

Setfill(symbol)

• Set the default fill character to x. (The default fill character is a space)

• It will use the symbol to fill out the space that has not been used by the data.

Special manipulators for numbers

• fixed• setprecision(n)

fixed

• Always show a decimal point and use a default of 6 digits after the decimal point. Fill with trailing zeros, if necessary.

setprecision(number)

• Set the floating-point precision to the places of number. If the fixed manipulator is designated, number specifies the total number of displayed digits after the decimal point; otherwise, it specifies the total number of significant digits displayed (both integer portion and fractional portion)

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Formatted Output (continued)

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Formatted Output (continued)

Links to several lists of basic C++ constructs

• A list of keywords• A list of operators, with associativity of each

and precedence among them.• A list of io flags and format manipulators• A c++ reference website• Literals• Tokens• identifiers

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