Maximum Sum of a Fix Size Sub-array(Sliding Window Technique)

#include<bits/stdc++.h>

using namespace std;

int MaximumSum(int a[], int n, int sz)

{

    if(n < sz)

        return -1;

    int maxsum = 0, currentsum = 0;

    for(int i=0; i<sz; i++)

        currentsum += a[i];

    maxsum = currentsum;

    for(int i=sz; i<n; i++)

    {

        currentsum = currentsum - a[i-sz] + a[i];

        maxsum = max(maxsum, currentsum);

    }

    return maxsum;

}

int main()

{

    int n, sz;

    cout << "Enter Array Size :: ";

    cin >> n;

    cout << "\nEnter Window Size :: ";

    cin >> sz;

    int a[n];  /// Declar a array

    cout << "\nEnter Array Element :: ";

    for(int i=0; i<n; i++)  /// Enter Array Element 10 40 10 30 20

        cin >> a[i];

    cout << "\n";

    int mx =  MaximumSum(a, n, sz);

    if(mx != -1)

        cout << "Maximum Sum :: " << mx << "\n";  /// 40 10 30 = 80 Maximum sum

    else

        cout << "Maximum Summation Not Found." << "\n";

    return 0;

}