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:

Generate OTP Number in dart - Rando...
Generate OTP Number in dart - Random Number generator
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');

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');
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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