Hi Guys, Welcome to **Proto Coders Point**, In this dart tutorial we will learn, **What is a prime number**, check if a given number in prime or not & a dart program to print prime number from 1 to N.

## What is a Prime Number?

A Prime Number in math are the numbers that are greater then 1 & are divisible by 1 or itself.

In other Words, A number that can’t be divided by any other number, rather then 1 or itself.

### Prime Number Examples

Eg:

**5 =>** 5 can’t be divided by any other numbers.**3 =>** 3 can’t be divided by any other numbers.**7 =>** 7 can’t be divided by any other numbers. **13 =>** 13 can’t be divided by any other numbers.

### Not a Prime Number Examples

Eg:

**4 =>** 4 is divisible by 2 so it not a prime number.**6 =>** 6 is divisible by 2 so it not a prime number. **8 =>** 8 is divisible by 2 so it not a prime number.**10 =>** 10 is divisible by 2 so it not a prime number.

If you observe you can see that, all the even number are not a prime number, except 2.

NOTE: 0 and 1 are always said to be not a prime number.

## How to check if a number is prime or not in dart

Let’s write dart programs to check if a number is prime or no.

### 1. Dart Program to check a number prime or no

In this dart program, we will initialize a Integer with a number value & then check if that number is prime or no.

void main(){ int i,m=0,flag=0; int num = 5; m=num~/2; for(i = 2;i<=m;i++){ if(num%i == 0){ print('$num is not a prime number'); flag=1; break; } } if(flag==0){ print('$num is prime number'); } }

### 2. check prime number using method in dart program

void main(){ // call method by passing a integer value to it checkPrime(5); checkPrime(8); checkPrime(13); checkPrime(76); checkPrime(7); } // a method that checks prime or not prime void checkPrime(int num){ int i,m=0,flag=0; m=num~/2; for(i = 2;i<=m;i++){ if(num%i == 0){ print('$num is not a prime number'); flag=1; break; } } if(flag==0){ print('$num is prime number'); } }

### 3. Prime number dart program – take input from user

So now in below code, the number to be checked is not predefined, Here the dart code will ask the user to enter a number to be checked whether it a prime or not

import 'dart:io'; import 'dart:math'; void main(){ print('Enter number to check prime or no'); int? num = int.parse(stdin.readLineSync()!); print('$num'); if(CheckPrime(num)){ print('$num is a prime'); }else{ print('$num is not a prime'); } } bool CheckPrime(int num){ if(num<=1){ return false; } for (int i = 2;i<=sqrt(num);i++){ if(num%i == 0){ return false; } } return true; }

### 4. Dart program to print prime number from 1 to N

Now let’s write a dart program to print all the prime numbers from 1 to N.

import 'dart:io'; import 'dart:math'; void main(){ print('Enter Nth'); int? N = int.parse(stdin.readLineSync()!); print('----------------------------'); for(int i=2;i<= N;i++){ checkPrime(i); } } void checkPrime(int num){ int i,m=0,flag=0; m=num~/2; for(i = 2;i<=m;i++){ if(num%i == 0){ flag=1; break; } } if(flag==0){ print('$num'); } }

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