题目前置知识

c++中的string判空

string Count;
Count.empty(); //正确
Count != null; //错误

c++中最大最小宏

#include <limits.h>INT_MAX
INT_MIN

字符串使用+发运算将字符加到字符串末尾

string Count;
string str = "liuda";
Count += str[i];

 题目概况

AC代码

#include <iostream>
#include <cstring>
#include <limits.h>
using namespace std;long long int count = 0;
string Count;
int findCount(string &str){int bit = 1;int n=str.size();for(int i=0;i<n;i++){if(str[i]>='0'&&str[i]<='9'){Count += str[i];}else if(!Count.empty()){break;}}if(!Count.empty()){for(int i=Count.size()-1;i>=0;i--){count += (Count[i]-'0')*bit;bit = bit * 10;	} 
//这里如果题目有负数的话，就不能这么做了。if(count<=INT_MAX&&count>=0){return count;}}return -1;
}int main(){string str;cin>>str;int result=findCount(str);cout<<result;return 0;
}