Mine

#include<stdio.h>

main() {

	FILE *f;	/* Arxeio to opoio diavazoume. */
	FILE *g;	/* Arxeio sto opoio tha mpei to encoded keimeno. */
	int kleidi;
	char c1, c2;
	char arx[50], char tel[50];

	printf("\n Eisagogi protipou keimenou: ");
	gets(oa);
	printf("\n Eisagogi arxeiou stoxou: ");
	gets(os);
	printf("\n Dose to kleidi gia tin (apo)kriptografisi: ");
	scanf("%d", &kleidi);
	
	f=fopen("oa", "r");
	if (!f){
		printf("\n To arxeio den vrethike. \n");
		return;
	}
	
	
	g=fopen("os", "w");
	if (!g){
		printf("\n Failure. \n");
		return;
	}

	
	kleidi=kleidi%25+1;
		
	while (! feof(f)) {
		c1=fgetc(f);

		if (c1>=65 && c1<=90) {
			c2=c1+k;
			if(c2>90)
				c2-=26;
			} else
				c2=c1;
		fputc(c2, g);
		putchar(c2);
	}

	fclose(f);
	fclose(g);
}