Example:

#include <stdio.h>

int main(void) {
	
	float  choice = 2.0f;
	
	switch(choice){
	    case 1:
	        printf("Case 1\n");
	        break;
	    case 2:
	        printf("Case 2\n");
	        break;
	    case 3:
	        printf("Case 3\n");
	        break;
	    case 4:
	        printf("Case 4\n");
	        break;
	    default:
	        printf("Case default\n");
	}
	
	return 0;
}

Output

prog.c: In function ‘main’:
prog.c:7:9: error: switch quantity not an integer
  switch(choice){
         ^~~~~~
prog.c:5:9: warning: variable ‘choice’ set but not used [-Wunused-but-set-variable]
  float  choice = 2.0f;
         ^~~~~~

How to fix?

Use only integral variables/values with the switch statement. In this example, we changed type of choice variable from float to int.

Correct code:

#include <stdio.h>

int main(void) {
	
	int choice = 2;
	switch(choice){
	    case 1:
	        printf("Case 1\n");
	        break;
	    case 2:
	        printf("Case 2\n");
	        break;	    
	    case 3:
	        printf("Case 3\n");
	        break;	    
	    case 4:
	        printf("Case 4\n");
	        break;	    
	    default:
	        printf("Case default\n");
	}
	
	return 0;
}

Output

Case 2