/in/foo.c: In function 'main':
/in/foo.c:4:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d%d",&a,&b);
  ^~~~~
/in/foo.c:4:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:4:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:11:6: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
      printf("29");
      ^~~~~~
/in/foo.c:11:6: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:11:6: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:13:6: warning: incompatible implicit declaration of built-in function 'printf'
      printf("28");
      ^~~~~~
/in/foo.c:13:6: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:9:6: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
    if(a%100==0)
      ^
/in/foo.c:16:4: warning: incompatible implicit declaration of built-in function 'printf'
    printf("28");
    ^~~~~~
/in/foo.c:16:4: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:19:3: warning: incompatible implicit declaration of built-in function 'printf'
   printf("31");
   ^~~~~~
/in/foo.c:19:3: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:21:3: warning: incompatible implicit declaration of built-in function 'printf'
   printf("30");
   ^~~~~~
/in/foo.c:21:3: note: include '<stdio.h>' or provide a declaration of 'printf'