/in/foo.c: In function 'main':
/in/foo.c:20:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d", &x);
  ^~~~~
/in/foo.c:20:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:20:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:26:4: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    printf("%d+%d=%d\n", x1, x2, x);
    ^~~~~~
/in/foo.c:26:4: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:26:4: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:21:6: warning: unused variable 'i' [-Wunused-variable]
  int i = 0;
      ^