foo.c: In function ‘main’:
foo.c:5:17: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘r’
    5 |         int a,b r;
      |                 ^
foo.c:6:25: error: ‘b’ undeclared (first use in this function)
    6 |         scanf("%d%",&a,&b);
      |                         ^
foo.c:6:25: note: each undeclared identifier is reported only once for each function it appears in
foo.c:10:17: error: ‘r’ undeclared (first use in this function)
   10 |                 r=aa%bb;
      |                 ^
foo.c:17:12: warning: missing terminating " character
   17 |     printf("%d,c);
      |            ^
foo.c:17:12: error: missing terminating " character
   17 |     printf("%d,c);
      |            ^~~~~~~
foo.c:18:20: error: expected expression before ‘return’
   18 |                    return 0;
      |                    ^~~~~~
foo.c:18:29: error: expected ‘;’ before ‘}’ token
   18 |                    return 0;
      |                             ^
      |                             ;
   19 | }
      | ~                            
foo.c:15:13: warning: variable ‘c’ set but not used [-Wunused-but-set-variable]
   15 |         int c;
      |             ^