In the previous article we have discussed Java Program to Check Hamming Number

In this article we are going to understand what Triangular number is and how we can check whether a number is Triangular or not in Java with examples.

## Program to Check Triangular Number

**Triangular numbers** are numbers formed by addition of consecutive numbers starting from 1.

Example : 1+2 = 3 1 + 2 + 3 = 6 1 + 2 + 3 + 4 = 10

In the above examples the numbers are Triangular numbers as they are sum of consecutive numbers from 1.

Let’s see different ways to check triangular number.

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**Approach :**

- Enter a number/declare a number and store it .
- We try adding the numbers from 1 to the number until we find an equivalent match.
- If there is an equivalent match found, then the number is said to be Triangular number.

### Method-1: By Using Static Value

import java.util.Scanner; public class TriangularNumber { public static void main(String args[]) { //A number declared int num = 21; if(isTriangularNumber(num)) { System.out.println(num+" is a Triangular number"); } else { System.out.println(num+" is Not a Triangular number"); } } // Function that checks whether a number is Triangular or not static boolean isTriangularNumber(int num) { // Sum is initialized to 1 and not 0 as our loop starts from 2 directly int sum = 1; boolean flag = false; // Loop that adds consecutive digits for(int i = 2; i<num; i++) { sum = sum + i; if(sum == num) { flag = true; break; } } return flag; } }

Output: 21 is a Triangular number

### Method-2: By User Defined Method

import java.util.Scanner; public class TriangularNumber { public static void main(String args[]) { //Taking the number as input from the user using scanner class Scanner scan = new Scanner(System.in); System.out.print("Enter a number : "); int num = scan.nextInt(); if(isTriangularNumber(num)) { System.out.println(num+" is a Triangular number"); } else { System.out.println(num+" is Not a Triangular number"); } } // Function that checks whether a number is Triangular or not static boolean isTriangularNumber(int num) { // Sum is initialized to 1 and not 0 as our loop starts from 2 directly int sum = 1; boolean flag = false; // Loop that adds consecutive digits for(int i = 2; i<num; i++) { sum = sum + i; if(sum == num) { flag = true; break; } } return flag; } }

Output: Case-1 Enter a number : 21 21 is a Triangular number Case-1 Enter a number : 22 22 is a Not Triangular number

### Method-3: C++ Program to Check Triangular Number

#include <iostream> using namespace std; int main() { int num,flag=0,sum=0; cout<<"Enter a number: "; cin>>num; int c=1; while(sum<num) { sum=0; for(int i=1;i<=c;++i) { sum+=i; } if(sum==num) {flag=1;break;} c++; } if(flag) cout<<"Triangle number"<<endl; else cout<<"Not Triangle number "<<endl; return 0; }

Output: Enter a number: 21 Triangular Number

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