大家看看有啥问题 出不了结果
#include <stdio.h>
#include <math.h>
char encode(char plain,int key);
char decode(char cipher,int key);
int main(void){
FILE *inp,*outp;
char p;
int key,choise;
printf("enter the key");
scanf("%d",&key);
printf("Do you want to 1.encode or 2.decode?");
scanf("%d",choise);
switch(choise){
        case1:
        inp=fopen("plaintext.txt","r");
        outp=fopen("ciphertext.txt","w");
         while((p=fgetc(inp))!=EOF)
               {
                fputc(encode(p,key),outp);
                }
          fclose(inp);
         fclose(outp);
         break;
         case2:
         inp=fopen("ciphertext.txt","r");
         outp=fopen("meassage.txt","w");
          while((p=fgetc(inp))!=EOF)
               {
                fputc(decode(p,key),outp);
                }
         fclose(inp);
         fclose(outp);
         break;}

return(0);
}


char encode(char plain,int key)
    {char result;
     result=(plain-65+key%26)%26+65;
     return(result);}
char decode(char cipher,int key)
     {char result;
      if(cipher-65>=(key%26)){result=(cipher-65+26-key%26)%26+65;}
      else{result=cipher+26-key%26;}
      return(result);}

[ 本帖最后由 tedwugood 于 2010-10-24 11:39 编辑 ]