#include
#include
#include
char* mishi(char a[], char b[]);//设置一个函数用来改变密匙.
char* duizhaobiao(char a);//得到对照表
char miwen(char a[], char b[]);
int main()
{
char ch1[50];
char ch[100];
char ch2[27];
gets(ch);//输入密匙
char p = mishi(ch, ch1);//得到密匙
char *p1 = duizhaobiao(p);
strcpy(ch2, p);
strcat(ch2, p1);
printf("该表是对应表%s", ch2);
printf("请输入明文\n");
char in[100];
gets(in);
miwen(ch2, in);
getch();
return 0;
}
char mishi(char a[], char b[])
{

for (int i = 0; i <= strlen(a); i++)
{
    for (int j = 0; j <= strlen(a); j++)
    if (a[i] == a[j] && i != j)
        a[j] = ' ';
}
int j = 0;
for (int i = 0; i <= strlen(a); i++)//处理空格
{
    if (a[i] != ' ')
    {
        b[j] = a[i];//用另一个数组保持密匙
        j++;
    }
    else
        continue;
}
b[j] = '\0';//使数组b成为字符串。
return b;

}
char* duizhaobiao(char a[])
{

char ch1[26] = { 0 };//初始化全为0，对照字母表只要重复为1.
char ch2[25];
for (int i = 0; i < strlen(a); i++)
{
    int j = 0;
    for (char ch = 'A'; ch <= 'Z'; ch++)
    {
        if (a[i] == ch)
            ch1[j]++;//参考桶排法.
        else
            j++;
    }
}
char ch = 'A';
int b = 0;
for (int i = 0; i < 26; i++)
{
    for (int j = 0; j >= ch1[i]; j--)
    {
        ch2[b] = ch;
        b++;
    }
    ch++;
}
ch2[b] = '\0';
return ch2;

}
char* miwen(char a[], char b[])
{
for (int i = 0; i <= strlen(b); i++)
{
int j = 0;
for (char ch1 = 'A'; ch1 <= 'Z'; ch1++)
if (b[i] == ch1)
{
printf("%c", a[j]);
}
else
j++;
}

}
记住只能大写，如果需要小写使用头文件

#include
#include
int main()
{
int a,b,c,d,e,f,g;
char surface[1000]="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char secret[1000];
gets(secret);
strupr(secret);
strcat(secret,surface);

for(f=0;f<strlen(secret);f++)
if(secret[f]==' ')

{for(g=f;g<strlen(secret);g++)
{
secret[g]=secret[g+1];

}
g--;

}
for(a=0;a<strlen(secret);a++)

for(b=a+1;b<=strlen(secret);b++)

        {
            if(secret[a]==secret[b])
        {
            for(c=b;c<strlen(secret);c++)
            secret[c]=secret[c+1];
            b--;            
        }
        }
printf("%s\n%s\n",surface,secret);  
char give[100];
char Fsurface[100];
char Fsecret[100];
strcpy(Fsurface,strlwr(surface));
strcpy(Fsecret,strlwr(secret));
strcat(Fsecret,strupr(surface));
strcat(Fsecret,strupr(secret));   
scanf("%s",give);
for(d=0;d<=strlen(give);d++)
    for(e=0;e<=strlen(Fsurface);e++)
    {
        if(give[d]==Fsurface[e])  
            printf("%c",Fsecret[e]);
    }