# How to print Identity matrix of given size in C++

In this tutorial, we will learn how to print an identity matrix of nth size in C++ with an example, algorithm, and a program.

An identity matrix is a square matrix with all the principal diagonal elements having value one and the rest of the elements having zero.

Printing an identity matrix in C++ program means the user just have to enter the size of the square matrix and the program will generate the identity matrix of entered size.

## Algorithm to print identity matrix of a given size

1. declare a variable to store the size of the matrix and make input.
2. start an outer loop from i = 0 to n,
3. start an inner loop inside an outer loop from j = 0 to n.
4. if i is equal to j, then print 1 else print 0.

## C++ program to print the identity matrix of a given size

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

int main(){
int n; //to store size of matrix

//taking input in variable n
printf("Enter the size: ");
cin>>n;

cout<<"\nIdentity matrix of size "<<n<<": \n";

//priting square matrix
for(int i = 0; i < n; i++){
for(int j = 0; j < n; j++){
if(i == j)
cout<<"1 ";
else
cout<<"0 ";
}
cout<<endl;  //changing to next row
}
return 0;
}```

Output:

```Enter the size: 5

Identity matrix of size 5:

1 0 0 0 0
0 1 0 0 0
0 0 1 0 0
0 0 0 1 0
0 0 0 0 1```

Time complexity: O(n^2) where n is the length of row and column of the identity matrix