C Program to Check Prime or Armstrong Number Using User-defined Function

Introduction

In C programming, creating functions for specific tasks like checking for prime numbers or Armstrong numbers can make your code more organized and reusable. A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. An Armstrong number (also known as a narcissistic number) is a number that is equal to the sum of its own digits each raised to the power of the number of digits.

In this article, you will learn how to implement user-defined functions in C to check for prime numbers and Armstrong numbers. Practical examples will guide you through the process of setting up these functions and utilizing them effectively in your programs.

Creating the Prime Number Checker Function

Define the Prime Number Function

1. Define a function that accepts an integer and returns 1 if the number is prime and 0 if it is not. This function will iterate up to the square root of the number to check for factors.

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   #include <stdio.h>
   #include <math.h>
   
   int isPrime(int num) {
       if (num <= 1) return 0;
       for (int i = 2; i <= sqrt(num); i++) {
           if (num % i == 0) return 0;
       }
       return 1;
   }

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   Here, the isPrime function checks each number from 2 to the square root of num. If any number divides num without a remainder, the function returns 0, indicating the number is not prime. If no divisors are found, it returns 1.

Using the Prime Number Function

1. Utilize the created function within a main program to check if a number is prime.

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   int main() {
       int number;
       printf("Enter a number to check if it is prime: ");
       scanf("%d", &number);
   
       if (isPrime(number))
           printf("%d is a prime number.\n", number);
       else
           printf("%d is not a prime number.\n", number);
   
       return 0;
   }

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   In this implementation, the user inputs a number, which is then passed to the isPrime function. The output informs whether the number is prime.

Creating the Armstrong Number Checker Function

Define the Armstrong Number Function

1. Define a function that identifies whether a number is an Armstrong number. This involves determining the number of digits, then checking if the sum of each digit raised to that power equals the original number.

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   int isArmstrong(int num) {
       int original = num, sum = 0, digits = 0, temp;
       while (num != 0) {
           digits++;
           num /= 10;
       }
       num = original;
   
       while (num != 0) {
           temp = num % 10;
           sum += pow(temp, digits);
           num /= 10;
       }
   
       return (original == sum);
   }

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   This function first counts the digits in num. It then sums the cubes of each digit and compares this sum to the original number. If they are the same, it returns 1.

Using the Armstrong Number Function

1. Add functionality in your main program to check if a number is an Armstrong number.

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   int main() {
       int number;
       printf("Enter a number to check if it is an Armstrong number: ");
       scanf("%d", &number);
   
       if (isArmstrong(number))
           printf("%d is an Armstrong number.\n", number);
       else
           printf("%d is not an Armstrong number.\n", number);
   
       return 0;
   }

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   Similar to the prime check, this snippet allows the user to input a number and utilizes the isArmstrong function to check if it's an Armstrong number.

Conclusion

Mastering user-defined functions in C for specific checks like determining prime or Armstrong numbers not only enhances program cleanliness but also improves its modularity and reusability. By incorporating these examples into C programs, you enhance both the functionality and educational value of your code, making complex checks more manageable and intuitive. Use these functions to refine your approach to solving problems in C, streamlining your codebase effectively.