In C I trying to do funtion of sum but the answer isn't the expected : I've been trying to do a program which it can sum to numbers, I want to do the one by funtions althought.

The funtion is call "sum", but program get " the sum is 0". What i need to debug ?

    #include <stdio.h>
    
    int sum()
    
    {
    	int a, b;
    	int answer;
    	answer = a+b;
    	return 0;
    }
    	
    int main()
         {
     		int var_a,  var_b;
     		int result;
     		
     		printf (" first number \n");
     		scanf ("%i",&var_a);
     		printf ("second number \n");
     		scanf ("%i",&var_b);
     			result = sum(var_a,var_b);
     			
     		printf(" The sum is %i", result);
     		
     		return 0; 		
         }

Sincerily
NIN.