/in/foo.c: In function 'main':
/in/foo.c:40:6: warning: unused variable 'len2' [-Wunused-variable]
  int len2 = cheng(num2, s2, n2);
      ^~~~
/in/foo.c:39:6: warning: unused variable 'len1' [-Wunused-variable]
  int len1 = cheng(num1, s1, n1);
      ^~~~