凯撒密码，C语言，求救！(c语言凯撒加密)
凯撒密码，C语言，求救！(c语言凯撒加密)
#include stdio.h
#include string.h
int main()
{
int i = 0;
int len = 0;
char ch;
char buf[256] = {0};
char nor[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 enc[26] = {'s','u','w','y','a','c','e','g','i','k','m','o','q','r','t','v','x','z','b','d','f','h','j','l','n','p'};
printf("Encode or Decode: ");
scanf("%c",ch);
printf("please input your string: ");
fflush(stdin);
gets(buf);
len = strlen(buf);
switch (ch)
{
case 'e':
case 'E':
for (i=0;ilen;i++)
{
buf[i] = enc[buf[i] - 'a'];
}
break;
case 'd':
case 'D':
for (i=0;ilen;i++)
{
buf[i] = nor[i];
}
break;
default:
printf("wrong input!\n");
}
printf("%s\n",buf);
return 0;
}
凯撒密码是一种非常古老的加密方法，相传当年凯撒大地行军打仗时为了保证自己的命令不被敌军知道，就使用这种特殊的方法进行通信，以确保信息传递的安全。他的原理很简单，说到底就是字母于字母之间的替换。下面让我们看一个简单的例子：“baidu”用凯撒密码法加密后字符串变为“edlgx”，它的原理是什么呢？把“baidu”中的每一个字母按字母表顺序向后移3位，所得的结果就是刚才我们所看到的密文。
#include stdio.h
main()
{
char M[100];
char C[100];
int K=3,i;
printf("请输入明文M(注意不要输入空白串)\n");
gets(M);
for(i=0;M[i]!='\0';i++)
C[i]=(M[i]-'a'+K)%26+'a';
C[i]='\0';
printf("结果是:\n%s\n",C);
}
#include iostream
#include string
using namespace std;
int main()
{
string code;//储存初始字符串
string d_code;//加密后的字符串
int i;
int n; //移位的个数
cout"Enter the string "endl;
cincode;
cout"how many step do you want to move ?"endl;
cinn;
for(i=0;icode.size();++i)
{
if(int(code[i])97)
{
if(int(code[i])+n122)
d_code[i]=int(code[i])+n-26;
else
d_code[i]=int(code[i])+n;
}
else if(int(code[i])+n90)
d_code[i]=char(int(code[i])+n-26);
else
d_code[i]=char(int(code[i]+n));
}
for(i=0;icode.size();++i)
{
coutd_code[i];
}
coutendl;
cout"Code = "codeendl;
return 0;
}
/*
和楼上的相比,或许 看上去很烦
ch[i] +=5;
if (ch[i] 'Z')
{
ch[i] -= 26;
}
可以改成和 楼上的 方法
等价于 ch[i] = 'A' + (ch[i] - 'A' + 5) % 26;
*/
# include stdio.h
# include stdlib.h //用到了system(); 不写 ,可以用 getchar();
#define strwidth 117 //定义长度
int main(void)
{
char ch[strwidth];
int i ;
printf("请输入密码:");
gets(ch); //输入数据,用gets(); 保留了空格
for (i = 0; i strwidth ;i++ )
{
if (ch[i] = 'a' ch[i] = 'z' ) //判断是否小写字母
{
ch[i] +=5;
if (ch[i] 'z') //不解释,我想这样,理解可能会方便点吧
{
ch[i] -= 26;
}
}
else if ( ch[i] = 'A' ch[i] = 'Z') //判断是否大写字母
{
ch[i] +=5;
if (ch[i] 'Z')
{
ch[i] -= 26;
}
}
}
printf("加密后为:%s\n" , ch); //输出数据
system("pause");
return 0;
}
/*
或者 这样
*/
# include stdio.h
# include stdlib.h //用到了system(); 不写 ,可以用 getchar();
#define strwidth 117 //定义长度
int main(void)
{
char ch[strwidth];
int i ;
printf("请输入密码:");
gets(ch); //输入数据,用gets(); 保留了空格
for (i = 0; i strwidth ;i++ )
{
if (ch[i] = 'a' ch[i] = 'z' || ch[i] = 'A' ch[i] = 'Z' ) //判断是否是字母
{
ch[i] +=5;
if ( ch[i]'Z' ch[i] = 'Z' + 5 || ch[i] 'z' )
{
ch[i] -= 26;
}
}
}
printf("加密后为:%s\n" , ch); //输出数据
system("pause");
return 0;
}
#include stdio.h
#define isletter( c ) ( ((c)='a'(c)='z') || ((c)='A'(c)='Z') )
void Enc( const char *str, char *out, int key )
{
int i = 0;
while( str[i] )
{
if ( isletter( str[i] ) )
{
out[i] = str[i] + key;
if ( ! isletter( out[i]) )
out[i] -= 26;
}
else
out[i] = str[i];
i++;
}
out[i] = 0;
}
void Denc( const char *str, char *out, int key )
{
int i=0;
while( str[i] )
{
if ( isletter( str[i] ) )
{
out[i] = str[i] - key;
if ( ! isletter( out[i] ) )
out[i] += 26;
}
else
out[i] = str[i];
i++;
}
out[i] = 0;
}
int main()
{
char out[100], out2[100];
Enc( "THE QUICK BROWn fox jumps over THE LAZY DOG", out, 3 );
printf( "%s\n", out );
Denc( out, out2, 3 );
printf( "%s\n", out2 );
}
