/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:5:2: warning: statement with no effect [-Wunused-value]
  for(a;a>0;a--)
  ^~~
/in/foo.c:15:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("%d",c);
  ^~~~~~
/in/foo.c:15:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:15:2: note: include '<stdio.h>' or provide a declaration of 'printf'