警告:忽略'int scanf(const char*，…)'的返回值，并使用属性warn_unused_result [-Wunused-result]声明。

I was solving a problem. The question goes like this: Jill & Jung love lucky numbers. The lucky numbers is obviously 4 & 7, if a decimal representation of positive numbers contains 4 & 7, the positive integer is considered lucky. For example I was solving a problem. The question goes like