C Exercises: Calculate the factorial of a given number

Last update on December 20 2024 13:04:19 (UTC/GMT +8 hours)

Write a C program to calculate the factorial of a given number.

Step-by-step explanation of how a typical C program calculates the factorial of a given number:

Include Standard Libraries: The program starts by including the standard input-output library (stdio.h) which allows the program to use functions like "printf()" and "scanf()".
Main Function: The "main()" function is the entry point of the program where execution begins.
Declare Variables: The program declares an integer variable, typically n, to store the number for which the factorial is to be calculated. Another variable, often called 'result', is initialized to 1 to store the factorial result.
Input the Number: The program prompts the user to enter a number and reads the input using the "scanf()" function. This input is stored in the variable 'n'.
Factorial Calculation (Using a Loop):

A loop (such as a "for" loop or "while" loop) runs from 1 to the given number 'n'.
In each iteration of the loop, the current value of the loop counter is multiplied by 'result', and the result is stored back in 'result'.
For example, if n is 5, the loop iterates as follows:

result = result * 1 (result is now 1)
result = result * 2 (result is now 2)
result = result * 3 (result is now 6)
result = result * 4 (result is now 24)
result = result * 5 (result is now 120)

Output the Result: After the loop completes, the program prints the value of 'result', which now holds the factorial of the input number 'n'.
Return Statement: The "main()" function returns 0 to indicate that the program executed successfully.

Visual Presentation:

Calculate the factorial of a given number

Sample Solution:

C Code:

#include <stdio.h>  // Include the standard input/output header file.

void main(){
  int i, f = 1, num;  // Declare variables 'i' for loop counter, 'f' to store factorial, 'num' for user input.

  printf("Input the number : ");  // Print a message to prompt user input.
  scanf("%d", &num);  // Read the value of 'num' from the user.

  for(i = 1; i <= num; i++)  // Start a loop to calculate factorial.
      f = f * i;  // Calculate factorial.

  printf("The Factorial of %d is: %d\n", num, f);  // Print the calculated factorial.
}

Output:

Input the number : 5                                                                                          
The Factorial of 5 is: 120

Explanation:

for (i = 1; i <= num; i++)
  f = f * i;

In the above for loop, the variable i is initialized to 1, and the loop will continue as long as i is less than or equal to the value of variable 'num'. In each iteration of the loop, the value of variable 'f' is updated by multiplying it with the value of i using the assignment operator (*=).

The loop will increment the value of i by 1, and the process will repeat until the condition i<=num is no longer true.

Flowchart:

C Programming Code Editor:

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