Programming Example

C Program - Factorial of a Number using Command Line Argument Program, By creating a function

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💻 Practical Program

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Problem Statement: Write a C program to calculate the factorial of a non-negative integer N. The factorial of a number N is defined as the product of all integers from 1 up to N. Factorial of 0 is defined to be 1. The number N is a nonnegative integer that will be passed to the program as the first command line parameter. Write the output to stdout formatted as an integer WITHOUT any other additional text. You may assume that the input integer will be such that the output will not exceed the largest possible integer that can be stored in an int type variable.

Program Code

#include <stdio.h>		// for printf
#include <stdlib.h>		// for function atoi() for converting string into int
// Function to return fact value of n
int fact (int n) 
{
  
if (n == 0)
    
return 1;
  
  else
    {
      
int ans = 1;
      
int i;
      
for (i = 1; i <= n; i++)
	{
	  
ans = ans * i;
	
}
      
return ans;
    
}

}


// argc tells the number of arguments
// provided+1 +1 for file.exe
// char *argv[] is used to store the
// command line arguments in the string format
int main (int argc, char *argv[]) 
{
  
// means only one argument exist that is file.exe
    if (argc == 1)
    {
      
    printf ("No command line argument exist Please provide them first \n");
      
    return 0;
        
    }
  else
    {
      
    int i, n, ans;
      
    // actual arguments starts from index 1 to (argc-1)
	for (i = 1; i < argc; i++)
	{
	  
    // function of stdlib.h to convert string
    // into int using atoi() function
	    n = atoi (argv[i]);
	  
 
    // since we got the value of n as usual of
    // input now perform operations
    // on number which you have required
	    
    // get ans from function
	    ans = fact (n);
	  
 
    // print answer using stdio.h libraryb

Output

Explanation

Example:

If the argument is 4, the value of N is 4. 
So, 4 factorial is 1*2*3*4 = 24.
Output: 24
The code below takes care of negative numbers but at the end of the page there
is easier code which though doesn't take negative numbers in consideration.

How to learn from this program

First read the algorithm, then study the program code line by line. After that, compare the code with the output and finally go through the explanation. This approach helps learners understand both the logic and the implementation properly.

Practice suggestion

After understanding this example, try to rewrite the same program without looking at the code. Then change some values or logic and run it again. This helps improve confidence and keeps learners engaged on the page for longer.