Java program to display prime numbers from 1 to 100 and 1 to n

The number which is only divisible by itself and 1 is known as prime number. For example 2, 3, 5, 7…are prime numbers. Here we will see two programs: 1) First program will print the prime numbers between 1 and 100 2) Second program takes the value of n (entered by user) and prints the prime numbers between 1 and n. If you are looking for a program that checks whether the entered number is prime or not then see: 

Program to display the prime numbers from 1 to 100

It will display the prime numbers between 1 and 100.

class PrimeNumbers
{
   public static void main (String[] args)
   {  
       int i =0;
       int num =0;
       //Empty String
       String  primeNumbers = "";

       for (i = 1; i <= 100; i++)         
       {        
          int counter=0;    
          for(num =i; num>=1; num--)
   {
             if(i%num==0)
      {
   counter = counter + 1;
      }
   }
   if (counter ==2)
   {
      //Appended the Prime number to the String
      primeNumbers = primeNumbers + i + " ";
   } 
       } 
       System.out.println("Prime numbers from 1 to 100 are :");
       System.out.println(primeNumbers);
   }
}

Output:

Prime numbers from 1 to 100 are :
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Program to display prime numbers from 1 to n

It will display all the prime numbers between 1 and n (n is the number, entered by user).

import java.util.Scanner;
class PrimeNumbers2
{
   public static void main (String[] args)
   {  
      Scanner scanner = new Scanner(System.in);
      int i =0;
      int num =0;
      //Empty String
      String  primeNumbers = "";
      System.out.println("Enter the value of n:");
      int n = scanner.nextInt();
      scanner.close();
      for (i = 1; i <= n; i++)      
      {        
         int counter=0;     
         for(num =i; num>=1; num--)
         {
     if(i%num==0)
     {
  counter = counter + 1;
     }
  }
  if (counter ==2)
  {
     //Appended the Prime number to the String
     primeNumbers = primeNumbers + i + " ";
  } 
      } 
      System.out.println("Prime numbers from 1 to n are :");
      System.out.println(primeNumbers);
   }
}

Output:

Enter the value of n:
150
Prime numbers from 1 to n are :
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 
97 101 103 107 109 113 127 131 137 139 149

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About Mariano

I'm Ethan Mariano a software engineer by profession and reader/writter by passion.I have good understanding and knowledge of AngularJS, Database, javascript, web development, digital marketing and exploring other technologies related to Software development.