If else

if else
The general format for these are,
if( condition 1 )
statement1;
else if( condition 2 )
statement2;
else if( condition 3 )
statement3;
else
statement4;

The else clause allows action to be taken
where the condition evaluates as false
(zero).

The following program uses an if else
statement to validate the users input to
be in the range 1-10.

#include <stdio.h>
main()
{
int number;
int valid = 0;
while( valid == 0 ) {
printf("Enter a number between 1 and 10 -->");
scanf("%d", &number);
if( number < 1 ) {
printf("Number is below 1. Please re-enter\n");
valid = 0;
}
else if( number > 10 ) {
printf("Number is above 10. Please re-enter\n");
valid = 0;
}
else
valid = 1;
}
printf("The number is %d\n", number );
}

Sample Program Output :
Enter a number between 1 and 10 --> 12
Number is above 10. Please re-enter
Enter a number between 1 and 10 --> 5
The number is 5

/* Illustates nested if else and multiple arguments to the scanf function.  */
#include <stdio.h>
main()
{
int    invalid_operator = 0;
char   operator;
float  number1, number2, result;
printf("Enter two numbers and an operator in the format\n");
printf(" number1 operator number2\n");
scanf("%f %c %f", &number1, &operator, &number2);
if(operator == '*')
result = number1 * number2;
else if(operator == '/')
result = number1 / number2;
else if(operator == '+')
result = number1 + number2;
else if(operator == '-')
result = number1 - number2;
else
invalid_operator = 1;
if( invalid_operator != 1 )
printf("%f %c %f is %f\n", number1, operator, number2, result );
else
printf("Invalid operator.\n");
}

Sample Program Output :
Enter two numbers and an operator in the format
number1 operator number2
23.2 + 12
23.2 + 12 is 35.2
The above program acts as a simple
calculator.