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Functions in C

Function for factorial (iteration)

C Program: Function for factorial (iteration)

C 
#include <stdio.h>


 


// Function declaration


int factorial(int n);


 


int main() {


    int num, result;


 


    // Input from user


    printf("Enter a positive integer: ");


    scanf("%d", &num);


 


    // Check for invalid input


    if (num < 0) {


        printf("Error: Factorial of a negative number doesn't exist.\n");


    } else {


        result = factorial(num);   // Function call


        printf("Factorial of %d = %d\n", num, result);


    }


 


    return 0;


}


 


// Function definition (iterative method)


int factorial(int n) {


    int fact = 1;


    for (int i = 1; i <= n; i++) {


        fact = fact * i;


    }


    return fact;


}

Output

 
OUTPUT 1 :
Enter a positive integer: 5
Factorial of 5 = 120


OUTPUT 2 :
Enter a positive integer: -4
Error: Factorial of a negative number doesn't exist.

Explanation

  1. Function factorial()
    • Takes an integer n as input.
    • Uses a for loop to multiply numbers from 1 to n.
    • Returns the factorial value to main().
  2. Main Function
    • Reads user input.
    • Checks if input is non-negative.
    • Calls factorial() and prints the result.

 

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