C program to check positive negative or zero using switch case

Write a C program to input a number and check positive negative or zero using switch case. Checking negative, positive or zero using switch case is little tricky. In this example, I will explain how to check positive negative or zero using switch case. However, it is not recommended way, it's just for learning.

Example
Input

Input number: 23

Output

23 is positive

How to check positive negative or zero using switch case

We already know how to check whether a number is positive, negative or zero using if else if. However, checking using switch case if little tricky since, switch works with constants.

Switch case expects an expression that must return a list of known constant. So first let us define expressions to check positive, negative or zero.
(num > 0) return 1 (true) for positive number, otherwise 0 (false).
(num < 0) check negative and return 1 for negative number, otherwise 0.
(num == 0) return 1 for zero, otherwise 0.

Next, to code this we will require nested switch. Step by step descriptive logic to check positive negative or zero using switch case.

1. Input number from user, store it in some variable say num.
2. First we will check for positive. Use expression to check positive in outer switch. Use switch(num > 0).
3. The above switch expression with either return 1 or 0. Hence for case 1: print positive number.
4. For case 0: write one more nested switch statement with expression to check negative number. Say switch (num < 0).
5. For above switch expression the number can either be negative or zero. Since outer switch already says its not positive.
6. Hence for case 1: print negative and for case 0: print zero.

Program to check positive negative or zero using switch case

/**
* C program to check positive negative or zero using switch case
*/
#include <stdio.h>

int main()
{
int num;

printf("Enter any number: ");
scanf("%d", &num);

switch (num > 0)
{
// Num is positive
case 1:
printf("%d is positive.", num);
break;

// Num is either negative or zero
case 0:
switch (num < 0)
{
case 1:
printf("%d is negative.", num);
break;
case 0:
printf("%d is zero.", num);
break;
}
break;
}

return 0;
}

Output

Enter any number: 23
23 is positive.

Enter any number: -22
-22 is negative.

Enter any number: 0
0 is zero.

Happy coding 😉 