C Language Example - Check Prime Number
A prime number (or prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. There are infinitely many prime numbers.
Example
#include <stdio.h>
int main()
{
int n, i, flag = 0;
printf("Enter a positive integer: ");
scanf("%d", &n);
for (i = 2; i <= n / 2; ++i)
{
// Condition for non-prime
if (n % i == 0)
{
flag = 1;
break;
}
}
if (n <= 1)
{
flag = 1; // 1 and 0 are not prime numbers
}
if (flag == 0)
printf("%d is a prime number", n);
else
printf("%d is not a prime number", n);
return 0;
}
Output:
Enter a positive integer: 29
29 is a prime number
Example - Check Prime Numbers Between Two Numbers
#include <stdio.h>
int main()
{
int low, high, i, flag;
printf("Enter two integers: ");
scanf("%d %d", &low, &high);
printf("Prime numbers between %d and %d are: ", low, high);
while (low < high)
{
flag = 0;
for (i = 2; i <= low / 2; ++i)
{
if (low % i == 0)
{
flag = 1;
break;
}
}
if (flag == 0)
printf("%d ", low);
++low;
}
return 0;
}
Output:
Enter two integers: 100 200
Prime numbers between 100 and 200 are: 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199
Example - Check Prime Numbers Between Two Numbers Using a Function
#include <stdio.h>
int checkPrimeNumber(int n);
int main()
{
int n1, n2, i, flag;
printf("Enter two positive integers: ");
scanf("%d %d", &n1, &n2);
printf("Prime numbers between %d and %d are: ", n1, n2);
for (i = n1 + 1; i < n2; ++i)
{
// Check if prime
flag = checkPrimeNumber(i);
if (flag == 1)
printf("%d ", i);
}
return 0;
}
// Function definition
int checkPrimeNumber(int n)
{
int j, flag = 1;
for (j = 2; j <= n / 2; ++j)
{
if (n % j == 0)
{
flag = 0;
break;
}
}
return flag;
}
Output:
Enter two positive integers: 10 30
Prime numbers between 10 and 30 are: 11 13 17 19 23 29