Why is this.

[Help]

Can someone tell me what this means.
I see it in alot of programs.
The part I am confused on is the
if((argc<2) || (argc>3))
{ proceed w. code

Why do they put that at the beginning of code ?

#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
void main(int argc, char *argv[])


    {
    unsigned char car, dump;
    FILE *in, *out;
    long int i, perc, cont;
    i=1;
    perc=1;
    cont=0;
    if ((argc<2) || (argc>3))


        	{

Thanks