Modular Programs
A large program should be organized as several interrelated segments, arranged in a logical order: The segments are called modules. A program which consists of such modules is called a modular program.
In C++, modules can be classes or functions.
We can think of a function as a program segment that transforms the data it receives into a finished result.
Each function must have a name. Names or identifiers in C++ can made up of any combination of letters, digits, or underscores selected according to the following rules:
- Identifiers must begin within an uppercase or lowercase ASCII letter or an underscore (_).
- You can use digits in an identifier, but not as the first character. You are not allowed to use special characters such as $, &, * or %.
- Reserved words cannot be used for variable names.
Examples:
DegToRadintersectaddNums
FindMax1_densityslope
Examples of invalid identifiers:
1AB3
E%6
while
Note: C++ is a case-sensitive language (i.e. upper and lower case characters are treated as different letters).
The main() function
The main() function is a special function that runs automatically when a program first executes.
All C++ programs must include one main() function. All other functions in a C++ program are executed from the main() function.
The first line of the function, in this case int main() is called a function header line.
The function header line contains three pieces of information:
- What type of data, if any, is returned from the function.
- The name of the function
- What type of data, if any, is sent into the function.
int main()
{
program statements in here
return 0;
}
Note: The line
return 0;
is included at the end of every main function. C++ keyword return is one of several means we will use to exit a function. When the return statement is used at the end of main as shown here, the value 0 indicates that the program has terminates successfully.
The cout Object
The cout object is an output object that sends data given to it to the standard output display device.
To send a message to the cout object, you use the following pattern:
cout << “text”;
The insertion operator, <<, is used for sending text to an output device.
The text portion of the statement is called a text string. Text string is text that is contained within double quotation marks.
Consider the following program.
Example
#include <iostream.h>
int main()
{
cout << "Hello world!”;
return 0;
}
The output of the above program:
Hello world!
Preprocessor Directives
Before you can use any runtime libraries in your program, you must first add a header-file into your program, using the #include statement. A header file is a file with an extension of .h that is included as part of a program and notifies the compiler that a program uses run-time libraries.
One set of classes you will use extensively in the next few chapters is the iostream classes. The iostream classes are used for giving C++ programs input capabilities and output capabilities.
The header file for the iostream class is iostream.h.
The #include statement is one of the several preprocessor directives that are used with C++.
The preprocessor is a program that runs before the compiler. When it encounters an #include statement, the preprocessor places the entire contents of the designated file into the current file.
Preprocessor directives and include statements allow the current file to use any of the classes, functions, variables, and other code contained within the included file.
Example: To include the iostream.h file you use the following statement:
#include <iostream.h>
An i/o manipulator is a special function that can be used with an i/o statement. The endl i/o manipulator is part of the iostream classes and represents a new line character.
Example:
cout << “Program type: console application” << endl;
cout << “Create with: Visual C++ “<< endl;
cout << “Programmer: Don Gesselin” << endl;
All statements in C++ must end with a semicolon. Large statements can span multiple lines of code.
Example:
cout << “Program type: console application,”
<< “Create with: Visual C++ “
<< “Programmer: Don Gesselin”;
Comments
Comments are lines that you place in your code to contain various type of remarks. C++ support two types of comments: line and block.
C++ line comments are created by adding two slashes (//) before the text you want to use as a comment.
Block comments span multiple lines. Such comments begin with /* and end with the symbols */.
Example:
void main()
{
/*
This line is part of the block comment.
This line is also part of the block
comment.
*/
cout << “Line comment 1 “;
cout << “Line comment 2 “;
// This line comment takes up an entire line.
}
All programs should contain comments. They are
remarks, insights, wisdom in code without affecting the program. The compiler ignores comments
.
