Question

C Programing

How would i edit this code to have it return the cipher text.

void vigenereCipher(char* plainText, char* k){

int i;

char cipher;

int cipherValue;

int len = strlen(k);

//Loop through the length of the plain text string

for(i=0; i<strlen(plainText); i++){

//if the character is lowercase, where range is [97 -122]

if(islower(plainText[i]))

{

cipherValue = ( (int)plainText[i]-97 + (int)tolower(k[i % len])-97 ) % 26 +97;

cipher = (char)cipherValue;

}

else // Else it's upper case, where letter range is [65 - 90]

{

cipherValue = ( (int)plainText[i]-65 + (int)toupper(k[i % len])-65 ) % 26 +65;

cipher = (char)cipherValue;

}

//Print the ciphered character if it is alphanumeric (a letter)

if(isalpha(plainText[i]))

{

printf("%c", cipher);

}

else //if the character is not a letter then print the character (e.g. space)

{

printf("%c", plainText[i]);

}

}

}

Answer 1

Answer:

// change return type to char* as we need to return the cipher text.
char* vigenereCipher(char* plainText, char* k)
{
int i;
char cipher;
int cipherValue;
int len = strlen(k);
char* cipherText = (char*)malloc(sizeof(plainText)*sizeof(char));

//Loop through the length of the plain text string
for(i=0; i<strlen(plainText); i++)
{
//if the character is lowercase, where range is [97 -122]
if(islower(plainText[i]))
{
cipherValue = ( (int)plainText[i]-97 + (int)tolower(k[i % len])-97 ) % 26 +97;
cipher = (char)cipherValue;
}
else // Else it's upper case, where letter range is [65 - 90]
{
cipherValue = ( (int)plainText[i]-65 + (int)toupper(k[i % len])-65 ) % 26 +65;
cipher = (char)cipherValue;
}

//Print the ciphered character if it is alphanumeric (a letter)
if(isalpha(plainText[i]))
{
// Assign the cipher to the cipherText instead of printing it.
*cipherText = cipher;
cipherText++;
}
else //if the character is not a letter then print the character (e.g. space)
{
// Assign the character to the cipherText instead of printing it.
*cipherText = plainText[i];
cipherText++;
}
}
  
return cipherText;
}