请问这道题是怎么填的

int main()
{
    char s1[80] = "abcdefg";
    char* str1 = s1;//指针指向字符串地址
    int n = 0;
    while (*str1 != NULL)//循环到指针==NULL时结束 证明到末尾了
    {
        n++;
        str1++;  //指向下一个地址
    }
    printf("n=%d", n);
    return 0;
}

1. s1
2. != '\0'
3. str1++;