C++ Write First Program

Earlier you learned about C++ program structure. In this article, you will learn to write about your first C++ program and program elements in detail.

The meat of the C++ is in main function, and before main we need to declare the header files.

Simple C++ Program

Let us consider an example program and then we discuss the program elements in detail. The program declare a header file required for standard input and output operations called iostream.

#include <iostream.h>

void main(void)

{

         //Variable declaration

        int number;

        // Reading input values

        cout << "Enter the a number:" ;

        cin >> number;

       // if block

       if (number > 100)

       {

           cout << "Number is greater than 100;

       }

}

The above program prints only when the number is greater than 100. That is, when the user input a number that is more than 100.

Variable Declaration

The main program begins with variable declaration. In C++ , you must declare your variable first and the syntax to declare the variable is:

<date_type> <indentifier1>, <identifier2>, ... <identifierN>;

For example,

int A;                         // variable declared as integer type

char ID1, ID2,ID3; // variable declared as character type

float Number;      // variable declared as floating type

Statements

A statement in C++ program perform some action. Every statement ends with a semi colon (;). The C++ statements can be divided into following category.

  • Simple statements
  • Expressions
  • Statement blocks

Simple Statements – This type of statement are instruction to get input, print output or any one line statement that ends with a semi-colon.

For example,

cout<<  ” Hello World ! “;

int number;

Sometimes a simple expression can also be a simple statement.

Expressions – An expression is a mathematical expression or an assignment that evaluates to a single value and ends with semi-colon. This type of statements use C++ operators.

For example,

result = number1 + number2;

area_of_triangle = ( 1/2 * base) * height;

We can write any type of complex expressions which depends on the problem we are solving.

Statement blocks – In the above program, if block is an example of statement block which encloses many simple statements.

For example,

if ( x == 0)
{
   area = 0;
}
else
{
   area = x * x;
}
cout << "Area = " <<  " " << area ;
}

The example above has two blocks – if block and else block. The if block contains only one statement – an expession and the else block contains two statements.

This the advantage of grouping the statements into blocks, so that you can execute then as part of a task. The else block above computes the area and prints the result.  Two actions were performed within a block.

Comments

C++ comments are lines ignored by the compiler. The compiler understands that the comments are not to be executed. The comments are of two types

  • Single line comment (//)
  • Multiline comment ( /* …. */)

Single Line Comment – You can write a single line of text as comment after (//) symbol. See the program above.

For example,

// this is a comment ignored by the compiler

// this is another line

Multiline Comment – Inherited from C language, C++ allows to add multiple lines as comments. Anything in between /* and */ is ignored. The multiple line comment is used for describing the program details. There is not restriction on white space or new line for multiline comments.

For example,

/*

Program Name: Tax Calculator

Program Author: Notesformsc.org

Program Description: The program receives inputs such as yearly income, tax rates and computes total tax payable by the employees.

Version: 1.0

*/

Common Mistakes While Writing C++ Programs

These are some common mistakes by beginners of C++ programming language.

  • Forget to add necessary header files
  • Spelling mistakes
  • Not initializing the variables
  • Not following a naming convention for variables.
  • Forget to add semi-colon at the end of the statement
  • Block is not closed

If you avoid the above mistakes , then you will have a clean and error free programs.

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