Prerequisite: Command_line_argument.

The problem is to find the largest integers among three using command line argument.

Notes:

• Command-line arguments are given after the name of the program in command-line shell of Operating Systems. To pass command line arguments, we typically define main() with two arguments : first argument is the number of command line arguments and second is list of command-line arguments.

int main(int argc, char *argv[]) { /* ... */ }

• atoi – Used to convert string number to integers

Examples:

Input  : filename 8 9 45
Output : 45 is largest

Input  : filename 8 9 9
Output : Two equal number entered

Input  : filename 8 -9 9
Output : negative number entered

During execution of program, we pass three integers along with filename of the program and then we will find the largest numbers among three.
Approach :

1. The program “return 1” if any of the two conditions satisfy:
   • If any two numbers are same, print the statement “two equal numbers entered”.
   • If any number is negative, print “negative number entered”.
2. Else “return 0” if three different integers are entered.

For better understanding run this code on your linux machine.

// C program for finding the largest integer
// among three numbers using command line arguments
#include

// Taking argument as command line
int main(int argc, char *argv[])
{
	int a, b, c;

	// Checking if number of argument is
	// equal to 4 or not.
	if (argc < 4 || argc > 5)
	{
		printf("enter 4 arguments only eg.\"filename arg1 arg2 arg3!!\"");
		return 0;
	}

	// Converting string type to integer type
	// using function "atoi( argument)"
	a = atoi(argv[1]);
	b = atoi(argv[2]);
	c = atoi(argv[3]);

	// Checking if all the numbers are positive of not
	if (a < 0 || b < 0 || c < 0)
	{
		printf("enter only positive values in arguments !!");
		return 1;
	}

	// Checking if all the numbers are different or not
	if (!(a != b && b != c && a != c))
	{
		printf("please enter three different value ");
		return 1;
	}
	else
	{
		// Checking condition for "a" to be largest
		if (a > b && a > c)			
			printf("%d is largest", a);

		// Checking condition for "b" to be largest	
		else if (b > c && b > a)
			printf ("%d is largest", b);

		// Checking condition for "c" to be largest..
		else if (c > a && c > b)
			printf("%d is largest ",c);
	}
	return 0;
}

Output :