2.1 Basic elements in c++

Program structures

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:

1. What type of data, if any, is returned from the function.
2. The name of the function
3. 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.