# C Program to print Twin prime numbers between two ranges

Last updated on September 23, 2020

## What are Twin Primes Numbers? #

Pair of prime numbers which differ by 2 is called Twin Prime. For example, the first 4 twin primes are:

```
(3, 5), (11, 13), (17, 19), (29, 31)
```

The following is a C program to print Twin prime numbers between two ranges:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | ```
/*******************************************************
Program to print Twin prime numbers between two ranges
*******************************************************/
#include<stdio.h> // include stdio.h library
int check_prime(int n);
int main(void)
{
int start, end;
printf("Enter start: ");
scanf("%d", &start);
printf("Enter end: ");
scanf("%d", &end);
for(int i = start; i < end; i++)
{
if(check_prime(i) && check_prime(i + 2))
{
printf("{%d, %d}\n", i, i + 2);
i = i + 1;
}
}
return 0; // return 0 to operating system
}
int check_prime(int n)
{
if(n == 1)
{
return 0;
}
for(int i = 2; i < n; i++)
{
if(n % i == 0)
{
// number is not prime
return 0;
}
}
// number is prime
return 1;
}
``` |

**Expected Output:** 1st run:

1 2 3 4 5 6 7 8 | ```
Enter start: 1
Enter end: 50
{3, 5}
{5, 7}
{11, 13}
{17, 19}
{29, 31}
{41, 43}
``` |

2nd run:

1 2 3 4 5 | ```
Enter start: 500
Enter end: 600
{521, 523}
{569, 571}
{599, 601}
``` |

## How it works #

In line 19, we have a for loop that iterates over the numbers between the specified range.

In line 21, we call `check_prime()`

number two times. Once with the number `i`

and once with the number `i + 2`

.

If the condition satisfies then `i`

and `i + 2`

are twin primes. In line 23, we print the twin prime numbers and in line 24, we increment the counter `i`

by `1`

, to check for the next number.

**Related Reading:**

- C Program to find Prime Numbers
- C Program to check whether the number is a Palindrome
- C Program to multiply two numbers using Russian peasant method
- C Program to find LCM and HCF of two numbers
- C Program to check whether the number is even or odd.

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