#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define NUM 1000

int main()
{
	int table[27];
	int i;
	for(i=1;i<=26;i++)
	{
		table[i]=96+i;
	}
	int count=0;
	char key[NUM],word[NUM];
	printf("密鑰: ");
	scanf("%s",key);
	printf("密文: ");
	scanf("%s",word);
	int k1,k2,k=0;	
	
	k1=strlen(key);
	k2=strlen(word);
	i=0;
	if(k1<k2)
	{
	   while(i<k2)
	   {
	     	key[i]=key[k];
	    	i+=1;
	    	k+=1;
	    	if(k%k1==0)
			{
		    	k=0;
			}
	   }
	}

	printf("\n明文: ");
	char *t;
	t=(char*)calloc(k2,sizeof(char));
	for(i=0;i<k2;i++)
	{
		if(key[i]<word[i])
		{
		t[i]=table[word[i]-key[i]+1];
		}
		else if(key[i]>word[i])
		{
			t[i]=table[26-(key[i]-word[i]-1)];
		}
		else if(key[i]==word[i])
		{
			t[i]=key[i];
		}
		printf("%c",t[i]);

	}

	printf("\n");
	system("pause");
	return 0;

}