Program to find prime number

In this post, you will learn how to write programmes in different languages to print prime numbers.

A prime number is a whole number greater than 1, whose only factors are 1 and itself, like -2, 3, 5, 7, 11, etc. For example, 17 is a prime number because it is only divisible by 1 and 17, on the other hand, 18 is not a prime number because it is divisible by 2, 3, 6, 9, and number itself.

Java print prime numbers from 1 to 20 using for loop

Here, we have used for loop to get prime numbers from 1 to 20. We loop over the number range (1 to 20) and check whether the number is prime or not. The for loop iterates from i=0 to i=given number, if the remainder of i/num = 0, then it increases the count by 1. After all the iterations, if counter=2, then that number is a prime number.

public class CheckPrimeNumbers
{
    public static void main (String[] args)
    {		
       int i =0;
       int num =0;
       
       String  prime_numbers = "";

       for (i = 1; i <= 20; i++)         
       { 		  	  
          int counter=0; 	  
          for(num =i; num>=1; num--)
    	  {
             if(i%num==0)
    	     {
     		    counter = counter + 1;
    	     }
    	  }
    	  if (counter ==2)
    	  {
    	     prime_numbers = prime_numbers + i + " ";
    	  }	
       }	
       System.out.println("Prime Numbers between 1 and 20 :");
       System.out.println(prime_numbers);
    }
}

Prime Numbers between 1 and 20 :
2 3 5 7 11 13 17 19 

PHP Prime Number Program using While Loop

The following PHP code prints a list of prime numbers between 1 and 100 (that is, numbers not divisible by something other than 1 or the number itself) using a while loop.

In the given code, we have two while loops. The inner while loop does the testing with each possible divisor. If the inner loop finds a divisor, the number is not prime, so it breaks out without printing anything, and if the testing gets as high as the square root of the number, we can assume that the number is prime. The outer loop works through all the numbers between 1 and 100. This loop is broken when we have reached the breaking point of numbers to test.

<?php  
	$limit = 30;
	$init = 2;
	
	while(TRUE)
	{
		$div = 2;
		if($init > $limit) 
		{
			break;
		}
		while(TRUE)
		{
			if($div > sqrt($init))
			{
				echo $init."  ";
				break;
			}
			if($init % $div == 0) 
			{
				break;
			}
			$div = $div + 1;
		}
		$init = $init + 1;
	}
?>

2  3  5  7  11  13  17  19  23  29  

Python Program to print Prime Numbers between interval

Python programme that uses a for loop to print prime numbers between a given interval. Numbers less than or equal to 1 are not prime numbers. That's why, we have started the range from 1.

for num in range(1, 50):  
   if num > 1:  
       for i in range(2,num):  
           if (num % i) == 0:  
               break  
       else:  
           print(num)  

2
3
5
7
11
13
17
19
23
29
31
37
41
43
47

C++ program to print Prime Number

The given C++ program takes the range and finds all the prime numbers between the range and also prints the number of prime numbers.

#include<iostream>
using namespace std;

//function to check for prime number
void prime(int num)
{
    int div=0;
    
    //checking for number of divisor
    for(int i=1;i<=num;i++)
    {
       if(num%i==0)
          div++;                
    }
    
    if(div==2)
      cout<<num<<endl;
}
int main()
{
    cout<<"Please enter range: ";    
    int min, max;
    
    cin>>min>>max;
    cout<<"Prime numbers between "<<min<<" and "<<max<<" are:"<<endl;
    
    //finding prime numbers in the given range
    for(int i=min;i<=max;i++)
            prime(i);
    return 0;
}

Please enter range: 20 40
Prime numbers between 20 and 40 are:
23
29
31
37

C Program to Find Prime Numbers in a given Range

The given C program takes the range and finds all the prime numbers between the range and also prints the number of prime numbers.

#include <stdio.h>

int main() {
   int min, max, i, flag;
   printf("Please enter range: ");
   scanf("%d %d", &min, &max);
   printf("Prime numbers between %d and %d are: ", min, max);

   // iteration until low is not equal to high
   while (min < max) {
      flag = 0;

      // ignore numbers less than 2
      if (min <= 1) {
         ++min;
         continue;
      }

      // if low is a non-prime number, flag will be 1
      for (i = 2; i <= min / 2; ++i) {
         if (min % i == 0) {
            flag = 1;
            break;
         }
      }

      if (flag == 0)
         printf("%d ", min);

      ++min;
   }
   return 0;
}

Please enter range: 50 70
Prime numbers between 50 and 70 are: 53 59 61 67 

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