# 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**

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

Also learn: Rotation of a square matrix by 90 degrees in C++

## 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

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