C++ Program to Print Prime numbers in a given range

Program to find Prime Numbers in a given range

Here we will discuss how to find prime numbers in the range specified by the user using C++ programming language.

Prime numbers are the numbers which have 2 divisors only i.e. the number that can be divided by 1 and the number itself then the number is a prime number.

Example: 2, 3, 5, 7, 11, 13………etc.

In this program, the user will specify a range and we will check for every number in the range for being prime

program to find the prime numbers in a given range

Working

Let’s see how the code works:

  • User gives two inputs(one for the lower limit & other for the upper limit).
  • The inputs are stored in two int type variables say lowerLimit, upperLimit.
  •  Start a loop that will run from lowerLimit till upperLimit with every increment equal to 1
    • For every value call a function prime() with that value as a parameter
    • prime() will tell whether a number is prime or not
      • Number of divisors of the number is found
      • If the number of divisors is equal to 2 then the number is a prime number
      • Otherwise the number is not a prime number.
  • All the prime numbers between lowerLimit and upperLimit are printed.

C++ Code

//C++ Program
//Prime numbers in a given range
#include<iostream>
using namespace std;
//function to chek 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++;
}
//no divisors other than 1 and itself
if(div==2)
cout<<num<<endl;
}
int main()
{
cout<<"Enter range:";
int lowerLimit, upperLimit;
//user input
cin>>lowerLimit>>upperLimit;
cout<<"Prime numbers between "<<lowerLimit<<" and "<<upperLimit<<" are:"<<endl;
//finding prime numbers in the given range
for(int i=lowerLimit;i<=upperLimit;i++)
prime(i);
return 0;
}

Output

Enter range:1
20
Prime numbers between 1 and 20 are:
2
3
5
7
11
13
17
19

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