//功能：乘数加密 K=3 5 7 9 11 15 17 19 21 23 25

#include <stdio.h>

int str_len(char *str)//求字符串的长度 {  int len = 0;  while(*(str++))   len++;  return len; } int main(int argc, char *argv[]) {  char a[26] = {'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 b[26] = {'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 str[50];  int k;  printf("Please input the words（必须是小写可以用函数改变） :");  gets(str);  printf("Please input the following number[3][5][9][11][15][17][19][21][23]:");//可以求逆元的数   scanf("%d",&k);  int len = str_len(str);  for(int i = 0;i<len;i++)   for(int j = 0;j<26;j++)   {    if(str[i]==a[j])     str[i] = b[(k*j)%26]//换    else     str[i] = str[i];//将空格等符号落下来    }   printf("%s\n",str);//打印  return 0; }

//解密

#include <stdio.h>

求字符串长度

int str_len(char *str) {  int len = 0;  while(*(str++))   len++;  return len; }

//求逆元

int mulny(int k) {  int t;  for(int i = 0;i<26;i++)  {   t=k*i;   if(t%26==1)    return i;  } }

int main(int argc, char *argv[])

{  char a[26] = {'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 b[26] = {'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 str[50];  int k;  printf("Please input the words :");  gets(str);  printf("Please input the following number[3][5][9][11][15][17][19][21][23]:");//26以内有逆元的数字  scanf("%d",&k);  int p = mulny(k);  int len = str_len(str);  for(int i = 0;i<len;i++)   for(int j = 0;j<26;j++)   {    if(str[i]==a[j])     str[i] = b[(p*j)%26];    else     str[i] = str[i];   }   printf("%s\n",str);  return 0; }

/*

会凯撒加密的这个应该没啥大问题，但是刚刚玩，我调试还是调试了一会的，我记得昨天都调好了，今天加密找不到了，存储代码的时候没规律。哎哎，又改的幸好不费劲。也许有错的地方希望提出改正，我想进步哦！谢谢大家。

 

*/