字符串中1的个数

#include<string>
#include<iostream>
using namespace std;

int main()
{
    string str="1hj1jk11jnk111jk1";
    int num=0;
    //cin>>str;
    for(unsigned int i=0;i<str.size();i++)
    {
        if(str.at(i)=='1')
            num++;
    }
    cout<<num<<endl;
    return 0;
}