C++ count letters and order them from an input file

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

struct litera{
    int ct;
    int numarul;
};

int main() {
    litera l[10];
    ifstream f("engleza.txt");
    ofstream o("engleza-iesire.txt");
    char S[100];
    int ct[256], i,j,k,temp;


    for (i = 0; i < 256;i++) {
        ct[i] = 0;
    }

    while (!f.eof()) {
        f.getline(S, 100);
        for (i = 0; S[i];i++) {
            if( (S[i] >= 'a') && (S[i] <='z')){
            ct[S[i]]++;
            }
        }
    }

    j = 0;

    for (i = 0; i < 256;i++) {
        if (ct[i]) {
            l[j].numarul = i;
            l[j].ct = ct[i];
            j++;
        }
    }

    cout << endl;

    for (k = 0; k < j - 1;k++) {
        for (i = 0; i < j - 1; i++) {
            if (l[i].ct < l[i+1].ct) {
                temp = l[i].ct;
                l[i].ct = l[i + 1].ct;
                l[i + 1].ct = temp;
                temp = l[i].numarul;
                l[i].numarul = l[i + 1].numarul;
                l[i + 1].numarul = temp;
            }
        }
    }

    for (i = 0; i < j;i++) {
        cout << char(l[i].numarul) << " " << l[i].ct;
        cout << endl;
      }


    system("pause");
}