Nested IF and ELSE IF Ladder

iii. Nested IF....ELSE
General Form:

if(conditional-expression)
{
    if(conditional-expression)
    {
        statements;
    }
    else
    {
        statements;
    }
    statements;
}
else
{
    if(conditional-expression)
    {
        statements;
    }
    statements;
}

In Nested if ..... else, the if and else part can contain one or more if else statements.

Sample Program : Find the largest among three input numbers.

   1:  #include<stdio.h>

   2:  #include<conio.h>

   3:  void main()

   4:  {

   5:      int a,b,c;

   6:      clrscr();

   7:      printf("Enter two numbers : ");

   8:      scanf("%d%d,%d",&a,&b,&c);

   9:      if(a>b)

  10:      {

  11:          if(a>c)

  12:          {

  13:              printf("%d is largest",a);

  14:          }

  15:          else

  16:          {

  17:              printf("%d is largest",c);

  18:          }

  19:      }

  20:      else

  21:      {

  22:          if(b>c)

  23:          {

  24:              printf("%d is largest",b);

  25:          }

  26:          else

  27:          {

  28:              printf("%d is largest",c);

  29:          }

  30:      }

  31:      getch();

  32:  }

iv. ELSE .... IF LADDER
General Form:

if(test condition)
{

}
else if(condition)
{

}
else if(condition)
{

}
else
{

}

This construct is known as the else if ladder.  The conditions are evaluated from the top of the ladder downwards.  As soon as a true condition is found, the statement associated with it is executed skipping the rest of the ladder.

Sample Program : Program to read two numbers and an operator which performs the specified operation and display the result.

   1:  #include<stdio.h>

   2:  #include<conio.h>

   3:  void main( )

   4:  {

   5:     float a,b,res;

   6:     char op;

   7:     clrscr( );

   8:     printf("Enter two Numbers : ");

   9:     scanf("%d%d",&a,&b);

  10:     printf("Enter the Operator : ");

  11:     scanf("%c",&op);

  12:     if(op=='+')

  13:          res=a+b;

  14:     else if(op=='-')

  15:          res=a-b;

  16:     else if(op=='*')

  17:          res=a*b;

  18:     else if(op=='/')

  19:          res=a/b;

  20:     else

  21:     {

  22:          printf("Invalid Operator ! \n Press any key to exit...");

  23:          getch( );

  24:          exit(0);

  25:     }

  26:     printf("%.2f %c %.2f = %.2f",a,op,b,res );

  27:     getch( );

  28:  }

The IF Statement

The 'IF' Statement is a powerful decision making statement and is used to control the flow of execution of statements.  It is basically a two way decision making statement and is used with an expression.  It takes the following form :

if (test condition)

It allows the computer to evaluate the test condition first and then depending on whether the value of the expression is true of false it transfers the control to a particular statement.

i. Simple IF
General Form :

if(test expression)
{
 statement block;
}
statement x;

If the test expression is true then statement block will be executed otherwise the statement block will be skipped and the execution will be jumped to the statement x.  When the condition is true both the statement block and the statement x are executed in sequence.

Sample Program : Find the absolute value of a given number.

   1:  #include<stdio.h>

   2:  #include<conio.h>

   3:  void main()

   4:  {

   5:      int num;

   6:      clrscr();

   7:      printf("Enter a number : ");

   8:      scanf("%d",&num);

   9:      if(num<0)

  10:      num=num*-1;

  11:      printf("Absolute Value : %d",num);

  12:      getch();

  13:  }

ii. The IF .... ELSE
General Form :

if(test condition)
{
 statement block1;
}
else
{
 statement block2;
}
statement x;

If the test expression is true, the statement block 1 will be executed otherwise the statement block 2 will get executed.  In both the situation statement x will be executed.

Sample Program : Find the largest among two input numbers.

   1:  #include<stdio.h>

   2:  #include<conio.h>

   3:  void main()

   4:  {

   5:      int a,b;

   6:      clrscr();

   7:      printf("Enter two numbers : ");

   8:      scanf("%d%d",&a,&b);

   9:      if(a>b)

  10:      {

  11:          printf("%d is largest",a);

  12:      }

  13:      else

  14:      {

  15:          printf("%d is largest",b);

  16:      }

  17:      getch();

  18:  }