Caesar Cipher Simple Program

Question

I've taken a code from here for a simple Caesar cipher, and I've modified it so that the user will define the cipher key. But the program crashes every time I tried to run it.

#include <stdio.h>

int main() 
{
    char array[100], cipher[100];
    int c=0, x=0, y=0;
    int z;
    printf("This Program will encrypt according to your needs\n");
    printf("Enter the cipher key\n");
    scanf("%d",&z);
    printf("Enter the sentence");
    while((c=getchar()) != '\n')
    {
        array[x++]=(char)c;
        cipher[y++]=(char)(c+z);
    }

    array[x]=0;
    cipher[y]=0;

    printf("%s\n",cipher);

    return 0;
}

Answer 1

It doesn't crash. The while loop ends instantly since the '\n' is in input buffer after scanf and this gets read first

Answer 2

The scanf that reads in the key leaves a newline in the input buffer. Then when you call getchar for the first time, it returns \n, so the while loop is never entered.

You're not actually crashing, but just never getting an opportunity to enter in the string to encode.

You need to add an extra call to getchar after the scanf but before the loop to consume the newline:

scanf("%d",&z);
getchar();

Answer 3

#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<ctype.h>
void main()
{
    char p[20];
    int key,i,enc;
    clrscr();
    printf("Enter Plain text=");
    gets(p);
    printf("\n Enter Key=");
    scanf("%d",&key);

    for(i=0;i<strlen(p);i++)
    {
           p[i]=tolower(p[i]);
           enc=((p[i]-97)+key)%26;
           printf("%c",enc+97);
    }
}

Answer 4

#include <stdio.h>
#include <conio.h>

void main()
    {
    int i, c;
    char str[100];

    printf("Enter the Text Message : ");
    gets(str);

    for (i = 0; i < strlen(str); i++)
        {
        switch (str[i])
            {
            case 'x':
                str[i] = 'a';
                continue;
            case 'y':
                str[i] = 'b';
                continue;
            case 'z':
                str[i] = 'c';
                continue;
            case 'X':
                str[i] = 'A';
                continue;
            case 'Y':
                str[i] = 'B';
                continue;
            case 'Z':
                str[i] = 'C';
                continue;
            }

        if (str[i] >= 'a' && str[i] < 'x')
            str[i] = str[i] + 3;
        else if (str[i] >= 'A' && str[i] < 'X')
            str[i] = str[i] + 3;
        }

    printf("Message After Encryption : \n");
    puts(str);
    for (i = 0; i < strlen(str); i++)
        {
        switch (str[i])
            {
            case 'a':
                str[i] = 'x';
                continue;
            case 'b':
                str[i] = 'y';
                continue;
            case 'c':
                str[i] = 'z';
                continue;
            case 'A':
                str[i] = 'X';
                continue;
            case 'B':
                str[i] = 'Y';
                continue;
            case 'C':
                str[i] = 'Z';
                continue;
            }

        if (str[i] >= 'd' && str[i] <= 'z')
            str[i] = str[i] - 3;
        else if (str[i] >= 'D' && str[i] < 'Z')
            str[i] = str[i] - 3;

        }
    printf("Message After Decryption : \n");
    puts(str);
    getch();
    }

Answer 5

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define MAXSIZE 1024

int main(int argc, char* argv[])
{
    char in[MAXSIZE];
    char en[MAXSIZE] = {0};

    //Input any Sting to encrypt in upper case or lower case
    //or also mixed-up in any case.
    read(STDIN_FILENO, in, MAXSIZE);
    encrypt(in, en);    
    printf("%s\n%s\n", in, en);
    bzero(in, strlen(in));
    decrypt(en, in);
    printf("%s\n%s\n", en, in);
    return 0;
}

int encrypt(char* input, char* cipher)
{
    int i;
    for(i = 0; i < strlen(input); i++)
    {
        if(input[i] >= 97 && input[i] <= 122)
        {
            cipher[i] = input[i]+23 <= 122 ? input[i] + 23 : input[i] - 3;
        }else if(input[i] >= 65 && input[i] <= 90)
        {
            cipher[i] = input[i]+23 <= 90 ? input[i] + 23 : input[i] - 3;
        }else
            cipher[i] = input[i];
    }
    return 0;
}

int decrypt(char* cipher, char* output)
{
    int i;
    for(i = 0; i < strlen(cipher); i++)
    {
        if(cipher[i] >= 97 && cipher[i] <= 122)
        {
            output[i] = cipher[i]-23 >= 97 ? cipher[i] - 23 : cipher[i] + 3;
        }else if(cipher[i] >= 65 && cipher[i] <= 90)
        {
            output[i] = cipher[i]-23 >= 65 ? cipher[i] - 23 : cipher[i] + 3;
        }else
            output[i] = cipher[i];
    }
    return 0;
}

Answer 6

Here is a complete code in C for Caesar cipher

#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<stdlib.h>
int main()
{
    int i,key;
    char plain[100],cipher[100];
    printf("Enter key:");
    scanf("%d",&key);
    key=key%26; // adjusting key
    fflush(stdin);
    printf("Enter text:");
    gets(plain);
    for(i=0;i<strlen(plain);i++)
    {
        if(isalpha(plain[i]))
        {
            if(islower(plain[i]))
                cipher[i]=(plain[i]+key-'a')%26+'a';
            else
                cipher[i]=(plain[i]+key-'A')%26+'A';
        }
        else
            cipher[i]=plain[i];
    }
    cipher[i]='\0';
    printf("After ciphering: %s",cipher);
    getch();
    return 0;
}