Вывести фрагмент строки

int main()
{
    char buf[500];
    cout << "Enter the line -> ";
    cin.getline(buf, 500);
    char *str = new char[strlen(buf) + 1];
    strcpy(str, buf);
 
    int m;
    cout << "Enter m -> ";
    cin >> m;
    int n;
    cout << "Enter n -> ";
    cin >> n;
 
    int length = n - m;
    char *resultStr = new char[length];
    for (int i = 0; i < length; i++, m++)
    {
            resultStr[i] = str[m];
    }
 
    cout << resultStr;
 
    delete[]str;
    delete[]resultStr;
 
    cout << "\n";
    system("PAUSE");
}

#define _CRT_SECURE_NO_WARNINGS
 
#include "matrix.h"
 
int main()
{
    char buf[500];
    std::cout << "Enter the line -> ";
    std::cin.getline(buf, 500);
    char *str = new char[strlen(buf) + 1];
    strcpy(str, buf);
 
    int m = 0, n = 0;
    std::cout << "Enter m -> ";
    std::cin >> m;
    std::cout << "Enter n -> ";
    std::cin >> n;
 
    if (n < m)
        std::swap(n, m);
 
    int length = n - m;
    char *resultStr = new char[length + 1];
    resultStr[length] = '\0';
 
    for (int i = m, j = 0; i < n; ++i, ++j){
 
        resultStr[j] = str[i];
    
    }
 
    std::cout << resultStr;
 
    delete[] str;
    delete[] resultStr;
 
    system("PAUSE");
    return 0;
 
}

int main()
{
    char str[500];
    cout << "Enter the line -> ";
    cin.getline(str, 500);
 
    int m;
    cout << "Enter m -> ";
    cin >> m;
    int n;
    cout << "Enter n -> ";
    cin >> n;
 
    int length = n - m;
    char *resultStr = new char[length + 1];
    for (int i = 0; i < length; i++, m++)
    {
            resultStr[i] = str[m];
    }
    resultStr[length] = '\0';
 
    cout << resultStr;
 
    delete[]resultStr;
 
    cout << "\n";
    system("PAUSE");
}