/in/foo.cc: In function 'void DeleteSubstring(char*, int, int)':
/in/foo.cc:7:26: error: 'strlen' was not declared in this scope
     int length = strlen(s);
                          ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:24:22: error: 'strcspn' was not declared in this scope
     s[strcspn(s, "\n")] = '\0';
                      ^