Bartek

#include<stdio.h>
int main()
{
    char msg[100], ch;
    int i,key;
    char mode;
    printf("Wcisniej D dla dekodowania lub Z dla kodowania\na");
    mode = getch();
    printf("Enter a plaintext  %c\n",mode);
    gets(msg);
    printf("Enter key");
    scanf("%d",&key);
    for(i=0;msg[i]!='\0';i++)
    {
        ch=msg[i];
        if(ch>='a'&&ch<='z')
        {
            if(mode == 'D' || mode == 'd')
                ch=ch-key;
            if(mode=='Z' || mode == 'z')
                ch=ch+key;

            if(ch>'z')
            {
                ch=ch-'z'+'a'-1;
            }
            msg[i]=ch;
        }
        else if(ch>='A'&&ch<'Z')
        {
            if(mode == 'D' || mode == 'd')
                ch=ch-key;
            if(mode=='Z' || mode == 'z')
                ch=ch+key;
            if(ch>'Z')
            {
                ch=ch='Z'+'A'-1;
            }
            msg[i]=ch;
        }
    }
    printf("Encrypted message: %s", msg);
    return 0;
}