Comments on my code?

[warbird]

Hi everyone. I started coding in C yesterday. This is my first language, except some java during highschool some 8 years ago. I was reading Arthur C. Clarkes book "The last theorem", where a theorem was presented (don't remember the name); For any whole number, using the following two rules, you will always end up with "1".

1 If even number, divide by two
2 If odd number, multiply by 3, and add 1.

I figured this would be a good challenge after my first "Hello World", and here is what I came up with.

#include <stdio.h>
int num;
int main ( int argc, char *argv[] )
{
	if (argc != 2)
	{
		printf("Usage: %s N\n",argv[0]);
		printf("N - integer");
		return 0;
	}
	{
		int num = atoi(argv[1]);
		printf("%d\n",num);
		while (num != 1)
		{
			if (num % 2)
			{
				/* Odd number. Multiply with 3 and add 1*/
				num = (num * 3)+1;
				printf("%d\n",num);
			}
			else
			{
				/* even number. divide by 2 */
				num = num / 2;
				printf("%d\n",num);
			}
		}
	}
	getchar();
}

If anyone has some constructive criticism or comments, it would be greatly appreciated. Maybe someone could show me how to check if the input parameter is an integer?

Best regards,

Jonas

[newb16]

scanf(argv[1],"%d",&value ) will return 0 if failed to convert the value. You may also check that num*3 is still within integer range (INT_MAX in limits.h).

[grayMist]

scanf(argv[1],"%d",&value )

Should rather be
sscanf(argv[1],"%d",&value ) ...