Why is this program(rather the segment) crashing the whole program

Question

I have been scratching my head to figure out why is my program is crashing. My aim was to scan a string and get frequency of each sub string !

The Real part where the program is crashing (M is a map of string,int type) My Input: the string is "abab" and the program crashes when i=0 and j is equal to 3 just at the M[e]++ statement!

    for(i=0;str[i];i++)
        {

            char temp[5001];
            k=0;
            cout<<str[i]<<endl;
            for(j=i;str[j];j++)
                {
                    temp[k]=(char)str[j];
                    k++;
                    temp[k]='\0';
                    string e(temp);
                    M[e]++;
                    cout<<j<<endl;
                }
        }

MAIN Method

    int main()
    {
    ini();
    int t,N,i,j,Q,buff,k=0;
    char str[5001];
    scanf("%d",&t);
    map <string ,int > M;
    map <string , int >::iterator ii;
    for(;t--;)
    {
        scanf("%d%d",&N,&Q);
        scanf(" %s",str);
        for(i=0;str[i];i++)
            {

                char temp[5001];
                k=0;
                cout<<str[i]<<endl;
                for(j=i;str[j];j++)
                    {
                        temp[k]=(char)str[j];
                        k++;
                        temp[k]='\0';
                        string e(temp);
                        M[e]++;
                        cout<<j<<endl;
                    }
            }
        for(ii=M.begin();ii!=M.end();++ii)
                F[ii->second]++;
        F2[N]=F[N]%MOD;
        for(i=N;i>=1;i--)
            if(F[i])
                for(j=i-1;j>=1;j--)
                    F2[j]=(F[j]+((long long)F[i]%MOD*C(F[i],j)%MOD)%MOD)%MOD;
        for(i=0;i<Q;i++)
           {
                scanf("%d",&buff);
                printf("%d\n",F2[buff]);
            }
        }
        return 0;
    }

Note

int F[5001],F2[5001];

are declared globally too.

Answer 1

As requested:

#include <iostream>
#include <string>
#include <map>

#define MOD 10

using namespace std;

int C( int a, int b ){
    return 5;
}

int F[5001],F2[5001];

int main()
    {
    int t,N,i,j,Q,buff,k=0;
    string str(5001, ' ');
    cin >> t;//scanf("%d",&t);
    cin.ignore( 256, '\n' );
    map <string ,int > M;
    map <string , int >::iterator ii;
    for(;t--;)
    {
        cin >> N;
        cin.ignore( 256, '\n' );
        cin >> Q;
        cin.ignore( 256, '\n' );
        //scanf(" %s",str);
        getline(cin,str);
        for(i=0;str[i];i++)
            {

                char temp[5001];
                k=0;
                cout<<str[i]<<endl;
                for(j=i;str[j];j++)
                    {
                        temp[k]=(char)str[j];
                        k++;
                        temp[k]='\0';
                        string e(temp);
                        M[e]++;
                        cout<<j<<endl;
                    }
            }
        for(ii=M.begin();ii!=M.end();++ii)
                F[ii->second]++;
        F2[N]=F[N]%MOD;
        for(i=N;i>=1;i--)
            if(F[i])
                for(j=i-1;j>=1;j--)
                    cout << "hello";F2[j]=(F[j]+((long long)F[i]%MOD*C(F[i],j)%MOD)%MOD)%MOD;
        for(i=0;i<Q;i++)
           {
                scanf("%d",&buff);
                printf("%d\n",F2[buff]);
            }
        }
        return 0;
    }

For testing purposes, because there was no MOD and C definitions given, for MOD I used a constant int and C an empty function that received those parameters and simply returned a value.

Instead of scanf, I used cin for the inputs and later cin.ignore() to clear the input buffer so that it won't skip the next cin. Changed str to type string. Used getline to get input for string, as this reads the enitre line from the input cin. And that is it for modifications.

Answer 2

        for(i=0;str[i];i++)
        {
            for(j=0;str[j+i];j++)
            {
                M[str.substr(j,i+1)]++;
            }
        }

Replace internal two for loops with this and check whether it's crashing or not . If still that means you may be running this program on windows.In that case use this.

        for(i=0;str[i];i++)
        {
            for(j=0;str[j+i];j++)
            {
                std::string sstr = str.substr(j,i+1);
                if ( M.find ( sstr ) == M.end() ){
                      M.insert( std::make_pair ( sstr , 0 ) ) ;
                }
                else
                M[str.substr(j,i+1)]++;
            }
        }