## Factorial Program in C Programming

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:

1. Factorial Program using loop,
2. Program using a function to find factorial and
3. 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.

Please comment if this post is useful to you or have any queries.

## Check Odd or Even Number using C Programming Language

Today I will show How can we check a number is odd or even in C Programming Language. We also use different method to identify even and odd numbers.

As we all know if we divide any number by 2 and the remainder is 0 (zero), then that number is Even, Otherwise its odd. We will use same logic here in C Programming. In C Programming we can get remainder by % (Modulus) operator.

For example of modulus operator, 3%2 gives 1 as remainder. Even numbers are in form of (2*x) and Odd numbers are in form of ((2*x)+1). Here ‘x’ is integer number.

## Program 1: Check whether number is even or odd using modulus operator

```#include<stdio.h>

main()
{
int n;

printf("Enter an integer\n");
scanf("%d",&n);

if ( n%2 == 0 )
printf("Even\n");
else
printf("Odd\n");

return 0;
}```

We can also check the whether the number is even or odd using bitwise operator & (AND).

For example, Binary of 9 is 1001. When we perform 9 & 1, The result will be 1 and you may observe that the least significant bit of every odd number is 1, so ( odd_number & 1 ) will be always one and also ( even_number & 1 ) is zero.

## Program 2: Check whether number is even or odd using Bitwise operator

```#include<stdio.h>

main()
{
int n;

printf("Enter an integer\n");
scanf("%d",&n);

if ( n & 1 == 1 )
printf("Odd\n");
else
printf("Even\n");

return 0;
}```

## Program 3: Check whether number is even or odd using Conditional Operator (Without using ‘if’ Conditional Operator)

```#include<stdio.h>

main()
{
int n;

printf("Input an integer\n");
scanf("%d",&n);

n%2 == 0 ? printf("Even\n") : printf("Odd\n");

return 0;
}```

In C Programming Language when we divide two integers we get an integer result.

For example the result of 7/3 will be 2. We can take advantage of this and can use it to find whether the number is odd or even. Consider an integer ‘n’ we can first divide by 2 and then multiply it by 2 if the result is the original number then the number is even otherwise the number is odd. For example 11/2 = 5, 5*2 = 10 (which is not equal to eleven), now consider 12/2 = 6 and 6 *2 = 12 ( same as original number). These are some logic which may help you in finding if a number is odd or not.

## Program 4: Check whether number is even or odd without using Modulus or Bitwise Operator

```#include<stdio.h>

main()
{
int n;

printf("Enter an integer\n");
scanf("%d",&n);

if ( (n/2)*2 == n )
printf("Even\n");
else
printf("Odd\n");

return 0;
}```