C Exercises: Find circular prime numbers upto a specific limit

Last update on March 19 2025 12:39:11 (UTC/GMT +8 hours)

28. Circular Prime Numbers Up to a Limit Variants

Write a program in C to find circular prime numbers up to a specific limit.

Sample Solution:

C Code:

# include <stdio.h>
# include <stdlib.h>
# include <stdbool.h>
# include <math.h>

int flg; // Global variable to store the flag indicating if the number is a circular prime or not

// Function to check if a number is prime
void chkPrime(long int n)
{
    long int i = n - 1; // Initialize 'i' to check divisibility of 'n'

    while (i >= 2) // Loop to check for divisibility of 'n' by numbers less than 'n'
    {
        if (n % i == 0) // If 'n' is divisible by 'i', set flag to 1 (not a prime number)
        {
            flg = 1;
        }
        i--; // Decrement 'i' to check the next number
    }
}

// Function to find all combinations of digits in the number and check for prime
void AllCombination(long int a)
{
    long int b, c, d, e, i, j, k, s, z, v, x[8], y[8], m;

    b = a;
    i = 0;

    // Extracting digits of the number and storing in an array 'y'
    while (b > 0)
    {
        y[i] = b % 10;
        b = b / 10;
        i++;
    }

    c = 0;

    // Reversing the order of digits and storing in array 'x'
    for (j = i - 1; j >= 0; j--)
    {
        x[c] = y[j];
        c++;
    }

    m = i;

    // Generating all possible combinations of digits
    while (m > 0)
    {
        c = m - 1;
        d = i - 1;
        e = 0;
        s = 0;

        while (e < i)
        {
            z = pow(10, d);
            v = z * x[c % i];
            c++;
            d--;
            e++;
            s = s + v;
        }
        m--;

        // Checking if the generated number is prime
        chkPrime(s);
    }
}

// Main function
int main()
{
    long int i = 2, ctr; // Variables to iterate through numbers and store the upper limit

    // Printing information about the program and asking for user input
    printf("\n\n Find Circular Prime Numbers up to a specific limit: \n");
    printf(" ---------------------------------------------------\n");
    printf(" Enter the upper Limit: ");
    scanf("%li", &ctr);
    printf("\n The Circular Prime Numbers less than %li are: \n", ctr);

    while (i <= ctr) // Loop to check for circular primes up to the given limit
    {
        flg = 0; // Resetting flag to 0
        AllCombination(i); // Calling function to check circular prime

        if (flg == 0) // Checking if the number is circular prime (flag is 0)
        {
            printf("%li ", i); // Printing circular prime number
        }
        i++; // Move to the next number
    }

    printf("\n"); // Print a new line after displaying circular prime numbers

    return 0; // Returning 0 to indicate successful execution
}

Sample Output:

 Enter the upper Limit: 1000                                                                                  
                                                                                                              
 The Circular Prime Numbers less than 1000 are:                                                               
2 3 5 7 11 13 17 31 37 71 73 79 97 113 131 197 199 311 337 373 719 733 919 971 991

Visual Presentation:

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to generate circular primes up to a user-defined limit and display each rotation.
• Write a C program to count circular primes in a range and output their rotation sequences.
• Write a C program to list circular primes and compare them with standard prime numbers.
• Write a C program to optimize circular prime generation using a pre-sieved prime list.

C Code Editor:

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