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

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

        /* This is a comment in C */

        printf("This is a C program\n");
	FILE *f = fopen("hello.txt", "w");
	if (f == NULL){
	    printf("Error opening file!\n");
    	    exit(1);
	}

	if (argc>1) {
        	printf("Hello %s !\n", argv[1]);
		fprintf(f, "Hello %s !\n",  argv[1]);
 	}else{
		printf("Hello world !\n");
		fprintf(f, "Hello world !\n");
	}

		/* print some text */
	fclose(f);
        printf("This is the end of my C program\n");
    	exit(0);

}