C if, if......else

The if Statement :-

                 C uses the keyword ' if ' to implement the decision control instruction. The general form of ' if ' statement looks like this:

if   ( this condition is true )

{   

execute the statement

 }

The keyword ' if ' tells the compiler that what follows is a decision control instruction. The condition following the keyword ' if  ' is always enclosed within a pair of parentheses. If the condition, whatever it is, is TRUE, then the statement is executed. If the condition is FALSE, then the statement is not executed.

// Program to display a number if user enters negative number

#include <stdio.h>
int main()
{
    int number;

    printf("Enter an integer: ");
    scanf("%d", &number);

    // Test expression is true if number is less than 0
    if (number < 0)
    {
        printf("You entered %d.\n", number);
    }

    printf("The if statement is easy.");

    return 0;
}

Output 2

Enter an integer: 5
The if statement is easy.

The else Statement :-

    Otherwise , if we want to add another statement by using else keyword if the condition is FALSE so that statement executed and we easily understand that the given condition is FALSE.

#include <stdio.h>
int main()
{
   int age;
   printf("Enter your age:");
   scanf("%d",&age);
   if(age >=18)
   {
 /* This statement will only execute if the
  * above condition (age>=18) returns true
  */
 printf("You are eligible for voting");
   }
   else
   {
 /* This statement will only execute if the
  * condition specified in the "if" returns false.
  */
 printf("You are not eligible for voting");
   }
   return 0;
}

Output:
Enter your age:14
You are not eligible for voting