# Display prime numbers between two intervals

posted May 20 1 min read

# Display prime numbers between two intervals

``````#include <stdio.h>

int main() {
int low, high, i, flag;
printf("Enter two numbers(intervals): ");
scanf("%d %d", &low, &high);
printf("Prime numbers between %d and %d are: ", low, high);

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

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

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

if (low % i == 0) {
flag = 1;
break;
}
}

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

// to check prime for the next number
// increase low by 1
++low;
}

return 0;
}``````

Prime numbers are the positive integers having only two factors, 1 and the integer itself. For example, factors of 6 are 1,2,3 and 6, which are four factors in total. But factors of 7 are only 1 and 7, totally two. Hence, 7 is a prime number but 6 is not, instead it is a composite no. But always remember that 1 is neither prime nor composite.

We can also say that the prime numbers are the numbers, which are only divisible by 1 or the number itself. Another way of defining it is a positive number or integer, which is not a product of any other two positive integers. There is no defined formula to find if a number is prime or not (except to a certain range), apart from finding its factors.