Factorial program in C Programming Language: C Program code to find and print factorial of a number.

Factorial can be achieved by three methods as follow:

- Factorial Program using loop,
- Program using a function to find factorial and
- Factorial Program using recursion.

Factorial is represented using ‘!’, so five factorial will be written as (5!), n factorial as (n!). Also n! = n*(n-1)*(n-2)*(n-3)…3.2.1 and zero factorial is defined as one i.e. 0! = 1.

## Factorial program in C Programming using ‘for’ loop

Here we find factorial using ‘for’ loop.

/** Write a c program to find the factorial of number using for loop **/ #include <stdio.h> int main() { int c, n, fact = 1; printf("Enter a number to calculate it's factorial\n"); scanf("%d", &n); for (c = 1; c <= n; c++) fact = fact * c; printf("Factorial of %d = %d\n", n, fact); return 0; }

Output:

Enter a number to calculate it's factorial 6 Factorial of 6 = 720

## Factorial program in C Programming using function

Here we find factorial using function.

/** Write a c program to find factorial of number using Funtion **/ #include <stdio.h> long factorial(int); int main() { int number; long fact = 1; printf("Enter a number to calculate it's factorial\n"); scanf("%d", &number); printf("%d! = %ld\n", number, factorial(number)); return 0; } long factorial(int n) { int c; long result = 1; for (c = 1; c <= n; c++) result = result * c; return result; }

## Factorial program in C Programming using recursion

Here we find factorial using Recursion.

/** Write a c program to find a factorial of number using Recursion **/ #include<stdio.h> long factorial(int); int main() { int n; long f; printf("Enter an integer to find factorial\n"); scanf("%d", &n); if (n < 0) printf("Negative integers are not allowed.\n"); else { f = factorial(n); printf("%d! = %ld\n", n, f); } return 0; } long factorial(int n) { if (n == 0) return 1; else return(n * factorial(n-1)); }

Recursion is a technique in which a function calls itself, for example in above code factorial function is calling itself. To solve a problem using recursion you must first express its solution in recursive form.

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