兄弟些看一下哪里出了问题

#include<stdio.h>
int main()
{
int a,b;
char c;
scanf("%d%d%c",&a,&b,&c);
switch(c)
{
case '+':
printf("%d",a+b);
break;
case '-':
printf("%d",a-b);break;
case '':
printf("%d",ab);break;
case '/':
if(b==0)
{
printf("Divided by zero!");
}

        else
        {
            printf("%d",a/b);
            }
        break;
    default:
        printf("Invalid operator!");break;
        
}
return 0;

}