Which type of triangle is ?

Write a function that receives three integer inputs for the lengths of the sides of
a triangle and returns one of four values to determine the triangle type
(1=scalene, 2=isosceles, 3=equilateral, 4=error).

#include<stdio.h>
int which_triangle(int a,int b,int c)
{
    if( !(a&&b&&c&&(a+b)>c&&(a+c)>b&&(b+c)>a) )
        return 4;
    else if(a==b && a==c)
        return 3;
    else if(a==b || a==c || b==c)
        return 2;
    else
        return 1;
}

int main()
{
    int a,b,c,x;
    printf("enter 3 side length : ");
    scanf("%d %d %d",&a,&b,&c);
    x=which_triangle(a,b,c);
    switch(x){
    case 1:
        printf("\nScalene Triangle\n");
        break ;
    case 2:
        printf("\nIsoscalene Triangle\n");
        break ;
    case 3:
        printf("\nEquilateral Triangle\n");
        break ;
    case 4:
        printf("\nError\n");
        break ;
    }// end of switch
return 0;
}

Let me know your thoughts.