girilen metni oteleme ile hem sifreler hem eski haline cozer...

sifrele_cozumle.c

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

const char character[] = {'a','b','c','d','e','f','g','h','i','j','k','l','m',
				'n','o','p','q','r','s','t','u','v','w','x','y','z',};
char *sifrele(char *dizi) {
	int i = 0, j;
	
	while (dizi[i]) {
		for (j = 0; dizi[i] >= 'a' && dizi[i] <= 'z' && dizi[i] != character[j]; j++ )
			;
       	        if(dizi[i] == character[j]) {
			j = (j+1)%26;
			dizi[i] = character[j];
		}
                //~ printf("%c",dizi[i]);
		i++;
	}
	printf("\n");
   	return dizi;
}

char *sifrecoz(char *dizi) {
	int i = 0, j;
	
	while(dizi[i]) {	
		for (j = 0; dizi[i] >= 'a' && dizi[i] <= 'z' && dizi[i] != character[j]; j++ )
			;
     	        if(dizi[i] == character[j]) {	
			j = (j-1)%26;
			dizi[i] = character[j];
		}
       	        //~ printf("%c",dizi[i]);
		i++;
	}
	printf("\n");
	return dizi;
} 

int main (void) {

    char *str = malloc(1024*sizeof(char));
    
    gets(str);
    printf("orjinal sozcuk : %s\n",str);
    
    char *sifreli = malloc(sizeof(str)+1);
    sifreli = sifrele(str);
    printf("sifreli sozcuk : %s\n",sifreli);
    
    char *cozulmus = malloc(sizeof(str)+1);
    cozulmus = sifrecoz(sifreli);
    printf("cozulmus sozcuk : %s\n",cozulmus);
    
    free(str);
    return 0;
}