/in/foo.c: In function 'main':
/in/foo.c:6:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%s",s);
  ^~~~~
/in/foo.c:6:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:6:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:12:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   printf("%d",m-n);
   ^~~~~~
/in/foo.c:12:3: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:12:3: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:14:3: warning: incompatible implicit declaration of built-in function 'printf'
   printf("%d",m+n);
   ^~~~~~
/in/foo.c:14:3: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:5:6: warning: unused variable 'flag' [-Wunused-variable]
  int flag=0;
      ^~~~