finding duplicates in string.cpp

#include <iostream>
#include<string.h>
using namespace std;
int main()
{
    char string[80];
    cout<<"Enter string: ";
    cin.getline(string,80);
    cout<<"\nDuplicate characters are following"<<endl;
    for(int i=0;i<strlen(string);i++){                     // nested loop statement
        for(int j=i+1;j<strlen(string);j++){
            if(string[i]==string[j]){                   // logic to detect duplicate character
                cout<<string[i]<<endl;                  // duplicate character
                break;
            }
        }
    }
    return 0;
}