# C Program to print Prime Numbers between 2 numbers coderinme

#### C Program to print Prime Numbers between 2 numbers

Do you know what is prime? Ok here we are every number that is only divisible by 1 or itself is prime so
we will write a C Program to print Prime Numbers between 2 numbers or interval that should be entered by User
This first program is simple here we are doing it in simple way

``````#include <stdio.h>
int main()
{
int low, high, i, flag;
printf("Enter two numbers(intervals): ");
// user can enter 2 value like 2 to 50
scanf("%d %d", &low, &high);

printf("Prime numbers between %d and %d are: ", low, high);
// here we check that number must be greater than 2
if(low<2)
low++;
while (low < high)
{
flag = 0;
// flag will do 0 and 1, 1 for not prime and 0 for prime
for(i = 2; i <low; ++i)
{
// checking if number is divisible by small or not
if(low % i == 0)
{

flag = 1;
break;
}
}
//print if not
if (flag == 0)
printf("%d ", low);

++low;
}

return 0;
}``````

But the program may takes much time complexity O(n*n) approx

##### Second program is small here we run the loop for n/2 times
``````#include <stdio.h>
int main()
{
int a, b, i, flag;
printf("Enter two numbers(intervals): please try to enter from at least 2 ");
scanf("%d %d", &a, &b);

printf("aPrime numbers between %d and %d are: ", a, b);
if(a<2)
a++;
while (a< b)
{
flag = 0;

for(i = 2; i <= a/2; ++i)
{
if(a% i == 0)
{
flag = 1;
break;
}
}

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

++a;
}

return 0;
}`````` This program is readable and so good with algo here complexity time is now O(n) approx

``````#include <stdio.h>
#include <math.h>
int main()
{
int a, b, i, flag;
printf("Enter two numbers(intervals): please try to enter from at least 2 ");
scanf("%d %d", &a, &b);

printf("Prime numbers between %d and %d are: ", a, b);
if(a<2)
a++;
while (a< b)
{
flag = 0;

for(i = 2; i <=sqrt(a); ++i)
{
if(a% i == 0)
{
flag = 1;
break;
}
}

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

++a;
}

return 0;
}``````

### hasectic

A web developer(Front end and Back end), and DBA at csdamu.com. Currently working as Salesforce Developer @ Tech Matrix IT Consulting Private Limited. Check me @about.me/s.saifi