C Program to Find Factorial of a Number

Factorials show up all over the place. Like when you're calculating permutations or combinations. For example, with a number like 5, the factorial is the product of all positive integers up to that point. So, 5! equals 5 * 4 * 3 * 2 * 1 = 120. Let’s whip up a C program to find the factorial of a number using a simple loop.

Prerequisites for the Factorial Program in C

Here's what you need to know before writing this program:

• Basic understanding of C syntax and structure.
• Using a loop, specifically a while loop.
• The stdio.h library for input/output functions.
• Any C compiler such as GCC 9 or newer — or just run it in the EduSeekho online compiler.

Source Code of C Program to Find Factorial of a Number

Here's the complete code for calculating the factorial:

#include <stdio.h>

int main() {
    int n, fact = 1;
    // Input from user
    printf("Enter a number: ");
    scanf("%d", &n);

    // Calculate factorial using a while loop
    while (n > 1) {
        fact *= n;
        n--;
    }

    printf("Factorial of %d = %d\n", n, fact);
    return 0;
}

Output of the Factorial Program

When you run this code, you can expect an output like this:

Enter a number: 5
Factorial of 5 = 120

Algorithm to Find Factorial in C

Finding a factorial involves multiplying the integer sequentially down to 1. Here is the step-by-step process the program follows:

1. Read the integer n from the user.
2. Set fact = 1 as the initial factorial value.
3. Repeat while n > 1:
4. Multiply fact by n.
5. Decrement n by 1.
6. Output the factorial result.

flowchart TD
  A([Start]) --> B[/Read n/]
  B --> C["fact = 1"]
  C --> D{"n > 1?"}
  D -->|Yes| E["fact = fact * n"]
  E --> F["n = n - 1"]
  F --> D
  D -->|No| G([End])

How the C Program to Find Factorial Works

Let's break down each line of the code:

• #include <stdio.h>: Includes the standard input/output library.
• int main(): The main function where the program execution begins.
• int n, fact = 1;: Declares integer variables n for input and fact initialized to 1 to hold the factorial result.
• printf("Enter a number: ");: Prompts the user to enter a number.
• scanf("%d", &n);: Reads the integer value from user input.
• while (n > 1): A loop that continues until n is greater than 1.
• fact *= n;: Multiplies fact by n to accumulate the factorial product.
• n--;: Decrements n for the next loop iteration.
• printf("Factorial of %d = %d\n", n, fact);: Outputs the factorial result to the console.
• return 0;: Ends the program successfully.

Time and Space Complexity of the C Factorial Program

Let's analyze the complexity of this factorial program:

Time complexity: O(n). Here, n is the number you input. For example, if you input 5, the loop runs 4 times (while (n > 1)). Each loop iteration does a multiplication and a decrement operation. If n is 10, it means 9 iterations.

Space complexity: O(1). The program uses only a fixed number of variables, specifically n and fact, both of which are integers and don't grow with the input size. This makes the space usage constant.

Key takeaway: Factorials grow super fast and can quickly exceed standard integer limits, so keep in mind to use the right data types for bigger numbers.

FAQs About C Program to Find Factorial of a Number

Here are some common questions students ask when writing this program:

Related Programs

If you found this program helpful, check out these related programs:

• C Program to Display Fibonacci Sequence with Example
• C Program to Add Two Integers with Explanation and Output
• C Program to Multiply Two Floating-Point Numbers
• C Program to Compute Quotient and Remainder Easily
• C Program to Generate Multiplication Table with Example

Conclusion

Factorial calculations pop up everywhere, from math studies to real-world uses, like calculating permutations. Experiment with different input sizes to see how quickly results balloon. Wanna dive deeper? Next, tackle prime number detection.

Put your C skills to the test in our C programming quiz and try out more code in the C online compiler.