Question

Write an algorithm and a C++ program that reverse the order of the elements of an array that is assumed to have been previously entered ("the first will be the last ..."). The reversion must be performed without the usage of any intermediary array.

Answer 1

#include <iostream>
using namespace std;

int main() {
    int size, temp;
    cout << "Enter size of array: ";
    cin >> size;
    int *arr = new int[size];

    cout << "Enter " << size << " elements: ";
    for (int i = 0; i < size; ++i) {
        cin >> arr[i];
    }

    for (int i = 0; i < size/2; ++i) {
        temp = arr[i];
        arr[i] = arr[size-i-1];
        arr[size-i-1] = temp;
    }

    cout << "Array in reverse is: ";
    for (int i = 0; i < size; ++i) {
        cout << arr[i] << " ";
    }
    cout << endl;

    delete[] arr;
    return 0;
}

Enter size of array: Enter 5 elements: Array in reverse is:971 2 4

Enter size of array: Enter 5 elements: Array in reverse is:971 2 4

Algorithm:

input size
input arr

for i from 1 to size/2
    swap arr(i) with arr(size-i-1)
end for

output arr