foo.c: In function ‘main’:
foo.c:41:28: warning: unused variable ‘num4’ [-Wunused-variable]
   41 |         int num1,num2,num3,num4;
      |                            ^~~~
foo.c:37:14: warning: variable ‘a’ set but not used [-Wunused-but-set-variable]
   37 |         char a = getchar();
      |              ^