C program that reads a non-negative
integer and computes its factorial

As stated in the question, the factorial of non-negative integer n is written n! and is defined as -
n! = n * (n – 1) * (n – 2) . . . 1 (for values of n greater than or equal to 1) and n! = 1 (for n = 0).
For example, consider n = 5, the n! = (5*4*3*2*1) = 120.

The following algorithm illustrates the computation of factorial of a non-negative integer 'n' -

START

Step 1: Read 'n'
Step 2: If n < 0 then let f = 0 else let f = 1
Step 3: Let i = n
Step 4: Repeat Step 4 to Step 6 for i >= 1
Step 5: f = f * i
Step 6: i = i - 1
Step 7: Print Factorial :- 'f'

STOP

/****************** Code starts here ****************/
#include<stdio.h>
#include<conio.h>

void main()
{
int n,i;
long f;

clrscr();
printf("Enter an integer: ");
scanf("%d",&n);
f=n<0?0:1;
for(i=n;i>=1;i--)
f*=i;
printf("Factorial = %ld",f);
}
/****************** Code ends here ****************/

OUTPUT :

Enter an integer: 5
Factorial = 120

Download source code here

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