凯撒密码程序的打印结果

Question

I'm trying to add "Encrypted message: " before the encrypted message is printed.

When I put the printf statement inside the "while" loop, I get something along the lines of: AEncrypred message: BEncrypted message: CEncrypted message: etc.

If I try and put the printf statement outside the loop, nothing prints.

Is there a way to print "Encrypted message: " before the result while still using putchar(); ?

#include <stdio.h>
#include <ctype.h>   

char encrypt(char in, int key) 
{
    if (isalpha(in)) 
    {  
        if (isupper(in)) 
        {
            return (((in-'A') + key) % 26) + 'A';
        }
        else 
        {
            return (((in-'a') + key) % 26) + 'a';
        }
    }
    else return in;
}

int main()
{
    int key;
    char ch, res;

    printf("Enter shift amount (1-25):\n");
    scanf("%d", &key);

    printf("Enter message to be encrypted:\n");
    getchar();

    while (ch != '\n') 
    {
        ch = getchar();
        res = encrypt(ch, key);
        putchar(res);
    }
    return 0;
}

Answer 1

#include <stdio.h>
#include <ctype.h>

char encrypt(char in, int key)
{
    if (isalpha(in))
    {
        if (isupper(in))
        {
            return (((in-'A') + key) % 26) + 'A';
        }
        else
        {
            return (((in-'a') + key) % 26) + 'a';
        }
    }
    else return in;
}

int main()
{
    int key;
    char ch, res;
    int checksum = 1;

    printf("Enter shift amount (1-25):\n");
    scanf("%d", &key);

    printf("Enter message to be encrypted:\n");
    getchar();

    while (ch != '\n')
    {
        ch = getchar();
        res = encrypt(ch, key);
        if(checksum) { checksum = 0; printf("Encrypted message: "); }
        putchar(res);
    }
    return 0;
}

I would use that way. If you don't like it.. let me know. I just solved it on a way that won't violate your code structure.

---

Your problem is putting the printf statement inside a loop. The loop will parse your printf statelement ? times , until ch equals new line. To prevent that you can use a variable outside the scope, initialized with a value for example 1 . To parse the printf statement once you do a condition if that variable equals its number and then assign 0 or another number to it. So in the next time the printf has to be parsed, it won't go, because the condition will be false.