凯撒密码.c

凯撒密码加密程序

#include <stdio.h>
void main() /*移位密码*/
{
    char c[100];   /*设置字符串数组以存储之后他要输入的明文*/
    int c_length, i=0, key=0;

printf("Please input primal sentence(请输入明文--一组英文字母): ");
    gets(c);
     c_length=strlen(c); /*取字符串c的长度放到length中*/
   printf("Input the key(0~25): ");
   scanf("%d", &key);
   getchar();

   if(key<0) /*判断密钥是否符合条件*/
   {
    printf("The value of key is error!\nPress any key to return...");

    return 0;
   }
/*若符合条件则开始加密明文*/
   for(i=0; i<c_length; i++)
   {
    if(c[i]>96&&c[i]<123) /*如果是小写字母*/
   {
    c[i] = c[i]-97;
    c[i] = (c[i]+key)%26;
    c[i] = c[i]+97;
    c[i] = c[i]-32;
    }
    else if(c[i]>64&&c[i]<91)   /*如果是大写字母*/
   {
     c[i] = c[i]+32;
     c[i] = c[i]-97;
     c[i] = (c[i]+key)%26;
     c[i] = c[i]+97;
   }
   }
   printf("对应密文为: %s\n", c);


    printf("Press any key to return");
}