###### tags: `leetcode`
# Question 28. Implement strStr()
### Description:
Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
### Solution:

string::npos
- string::npos作為string的成員函式的一個長度引數時，表示“直到字串結束（until the end of the string）”
- 它必須定義為 string::size_type

### AC code

#include <string.h>
class Solution {
public:
    int strStr(string haystack, string needle) {
        size_t pos = haystack.find(needle);
        if(pos==string::npos)
            return -1;
        else
            return pos;
    }
};