用C语言编程恺撒密码加密解密程序

用C语言编程恺撒密码加密解密程序

#include #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 );}