# C++ program to separate even and odd numbers from an array

## C++ program to separate even and odd numbers from an array of integers. Put all even numbers first, and then odd numbers.

Given: An array having even and odd integers. We have to segregate even and odd integers and put even numbers first and then odd numbers.

Example:

Input: {2, 5, 1, 10, 3, 6, 7, 8}

Output: 2 8 6 10 3 1 7 5

### # Algorithm

1. Initialise two index variables left = 0 and right = n-1.
2.  We have to increment the left index until we see an odd number.
3.  We have to decrement the right index until we see an even number.
4.  If left < right then swap array[left] and array[right].

Code:

#include<iostream>
using namespace std;
void swap(int * x, int * y){
int t = * x;

x = * y;
y = t;
}

void segregate(int array[], int n){
int left = 0, right = n - 1;
while (left < right){
while (array[left] % 2 == 0 && left < right)
left++;
while (array[right] % 2 == 1 && left < right)
right--;
if (left < right){
swap( & array[left], & array[right]);
left++;
right--;
}
}
}
int main(){
int array[100], n, i;
cout << "Enter number of elements: ";
cin >> n;
cout << "\nEnter elements: ";
for (i = 0; i < n; i++)
cin >> array[i];
cout << "Original array: ";
for (int i = 0; i < n; i++)
cout << array[i] << " ";
segregate(array, n);
cout << "\nArray after divided: ";
for (int i = 0; i < n; i++)
cout << array[i] << " ";
return 0;
}