PROGRAM 58

Object

Write a program to read a number and print whether it is a prime number or not.

Algorithm

1. Declare integer variables num and i.
2. Read num.
3. Set i = 2.
4. Repeat WHILE i < num
   • IF num mod i = 0, then
     • Break out of loop.
   • ELSE
     • i++.
   • [End of IF-ELSE structure.]
   • [End of WHILE loop.]
5. IF num = i, then
   • Write “The number is a prime number”.
   • ELSE
     • Write “The number is not a prime number”.
   • [End of IF-ELSE structure.]
6. Exit.

Flowchart

C++ Source Code

// program 58
#include<iostream>
using namespace std;

int main()
{
  int num, i = 2;
  cout << "Enter a number: ";
  cin >> num;

  while (i < num)
  {
    if (num % i == 0)
      break;
    else
      i++;
  }

  if (num == i)
    cout << "The number " << num << " is a prime number.";
  else
    cout << "The number " << num << " is not a prime number.";

  return 0;
}

C Source Code

/*program 58*/
#include<stdio.h>

int main()
{
  int num, i;
  printf("Enter a number: ");
  scanf("%d", &num);

  i = 2;
  while(i<num)
     {
     if(num%i==0)
	break;
     else
      i++;
     }
     if(num==i)
	printf("The number %d is a prime number.", num);
     else
	printf("The number %d is not a prime number.", num);
  return 0;
}

Output

Enter a number: 5
The number 5 is a prime number.