Aide compréhension programme en C

#include<stdio.h>
#include<stdlib.h>

int main(int argc, char * argv [])
{
	double laf, temp, st, ast;
	char c;
	FILE *in, *out;

	if(argc>1)
		in = fopen(argv[1], "r");
	if(argc==1 || in == NULL)
		in = fopen("in.xml", "r");

	if (in == NULL) {
		fprintf(stderr, "Erreur in\n");
		exit(1);
	}

	if(argc>2)
		out = fopen(argv[2], "w");
	if(argc<=2 || in == NULL)
		out = fopen("out.txt", "w");

	if (out == NULL) {
		fprintf(stderr, "Erreur out\n");
		exit(1);
	}
	else
	{
		fprintf(out, "| LAF\t| Temperature\t| Stokes \t\t\t| Antistokes\t\t|\n|\t\t|\t\t\t\t|\t\t\t\t\t|\t\t\t\t|\n"); // structure tab
		while ((c = fgetc(in)) != EOF)
		{

			if(fscanf(in, "<data id=\"1\">%lf,%lf,%lf,%lf</data>", &laf, &temp, &st, &ast) == 4)
				fprintf(out, "| %05.1lf\t| %010.6lf\t| %012.6lf\t| %012.6lf\t|\n|\t\t|\t\t\t\t|\t\t\t\t\t|\t\t\t\t|\n", laf, temp, st, ast); 
	}

	return 0;
}