Demonstration Of If Statement |

Demonstration Of If Statement

Example:1

        main()                    {
          int num;
          printf("Enter a number lessthan 10");
          scanf("%d",&num);
          if(num<=10)
          printf(" How nice you are");
        }
Description:
               On execution of this program, if you type a number less than or equal to 10, you get a message on the screen through printf(). If you type some other number the program doesn't do anything.

               To make you comfortable with the decision control instruction  one more example has been given below:

Example:2
 
             While purchasing certain items,a discount of 10% is offered if the quantity purchased is more than 1000.



         If quantity and price per item are input through the keyboard , while a program to calculate the total expenses.


      main()

      {         
        int qty,dis=0;

        float rate,tot;

        printf("Enter quantity and rate");

        scanf("%d%f",&qty,&rate);

        if(qty>1000)

        dis=10;

        tot=(qty*rate)-(qty*rate*dis/100);

        printf("total Expenses = Rs.%f",tot);

      }

        Here is some sample interaction with the program:

Enter quantity and rate 1200 15.50

Total  expenses = Rs 16740.000000

Enter quantity and rate  200 15.50

Total expenses = Rs 3100.00000

Description:
                 In the first run of the program, the condition evaluates to true, as 1200 (value
of qty) is greater than 1000. Therefore, the variable dis, which was earlier set to 0,now gets a new value 10. using this new values total expenses are calculated and printed.

   Is the statement dis=0 necessary ?

             The  answer is YES, since in C, a variable if not specifically initialized contains some unpredic table values( garbage value).

   We can even use Arithmetic Expressions in the "IF"   statement. For example all the following "IF" statements are valid.             

           if(3+2%5) 
            printf("This works");

           if(a=10)
              printf("Even this works");   

           if(-5)
              printf("Surprisingly  even this also works");

            Note That in C a non-zero value is considered to be true, where as a '0' is considered to be FALSE.In the first "IF" , the expression evaluates to 5 and since 5 is a non-zero,it is considered to be TRUE. Hence the printf() gets executed In the second "IF" , 10 gets assigned to a so the if is now reduced to if(a) or if(10) Since 10 is a non-zero, it is TRUE hence again printf() goes to work.
In  the third "IF", -5 is a non-zero number, hence TRUE. So again printf() goes to work. In place of -5 even if a  float like 3.14 were used it would be considered to be TRUE.So the issue is not whether the number is integer or float, or whether the number is positive or negative.Issue is whether it is zero or non-zero.