NHAY Doubt

#include<bits/stdc++.h>
using namespace std;
void child(int*,string);
void parent(int*,string,string);
int main()
{
    int i,j,k,length;
    string needle,haystack,temp1,temp2;
    while(cin>>length)
    {
        needle+='0';
        haystack+='0';
        cin>>temp1>>temp2;
        needle+=temp1;
        haystack+=temp2;
        if(needle.length()>haystack.length()){
            cout<<endl;
            needle.clear();
            haystack.clear();
            continue;
        }
        int lps[needle.length()];
        child(lps,needle);
        parent(lps,needle,haystack);
        needle.clear();
        haystack.clear();
        cout<<endl;
    }
    return 0;
}
void child(int lps[],string needle)
{
    int i=2,j,len=0;
    lps[1]=0;
    while(i<needle.length())
    {
        if(needle[i]==needle[len+1])
        {
            len++;
            lps[i++]=len;
        }
        else
        {
            if(len!=0)
            {
                len=lps[len];
            }
            else{
                lps[i++]=0;
            }
        }
    }
}
void parent(int lps[],string needle,string haystack)
{
    int i=1,len=0;
    while(i<=haystack.length()){
            //cout<<i<<" "<<len+1<<endl;
            if(len==needle.length()-1){
                cout<<i-len-1<<endl;
                len=lps[len];
            }
            if(i>=haystack.length())
                break;
        if(haystack[i]==needle[len+1]){
            len++;
            i++;
        }
        else{
            if(len!=0){
                len=lps[len];
            }
            if(len==0){
                i++;
            }
        }
    }
}

Can someone help me in finding out why it is not getting accepted, What changes should i make to correct this code?