Unprinted characters attaching to string - c

Question

I'm working on an encryption program for a class in C. I use modulo 27 math to perform the encryption. I add each encrypted character to an array but I've noticed that unprinted characters are also being added to my string at the end. I realized this when I checked the word count of the encrypted text and it contained more characters than the original text that was encrypted. Can anyone explain why this is happening? This is taking into account the newline at the end of the texts.
Plaintext = THE RED GOOSE FLIES AT MIDNIGHT STOP - wc is 37
Ciphertext = ACBVKWNOGMMMPQHNI XL QBJXDPNVIQVSNZN - wc is 40
//Go through each character of the plaintext
for (i = 0; i < size; i++)
{
//Convert the characters to an integer
PlainNums[i] = charInt(plaintext[i]);
KeyNums[i] = charInt(key[i]);
//Add the int from plain text and the key together
CipherNums[i] = PlainNums[i] + KeyNums[i];
if (CipherNums[i] > 27) //Wrap around if the number exceeds 27
{
CipherNums[i] -= 27;
}
CipherNums[i] = CipherNums[i] % 27; //Use modulo 27 math to generate a new integer
cipherText[i] = IntChar(CipherNums[i]);
}
int charInt(char c)
{
switch (c)
{
case 'A': return 0;
case 'B': return 1;
case 'C': return 2;
case 'D': return 3;
case 'E': return 4;
case 'F': return 5;
case 'G': return 6;
case 'H': return 7;
case 'I': return 8;
case 'J': return 9;
case 'K': return 10;
case 'L': return 11;
case 'M': return 12;
case 'N': return 13;
case 'O': return 14;
case 'P': return 15;
case 'Q': return 16;
case 'R': return 17;
case 'S': return 18;
case 'T': return 19;
case 'U': return 20;
case 'V': return 21;
case 'W': return 22;
case 'X': return 23;
case 'Y': return 24;
case 'Z': return 25;
case ' ': return 26;
default: return -1;
}
}
char IntChar(int n)
{
switch(n)
{
case 0: return 'A';
case 1: return 'B';
case 2: return 'C';
case 3: return 'D';
case 4: return 'E';
case 5: return 'F';
case 6: return 'G';
case 7: return 'H';
case 8: return 'I';
case 9: return 'J';
case 10: return 'K';
case 11: return 'L';
case 12: return 'M';
case 13: return 'N';
case 14: return 'O';
case 15: return 'P';
case 16: return 'Q';
case 17: return 'R';
case 18: return 'S';
case 19: return 'T';
case 20: return 'U';
case 21: return 'V';
case 22: return 'W';
case 23: return 'X';
case 24: return 'Y';
case 25: return 'Z';
case 26: return ' ';
default: return '!'; //error
}
}

Answer 1

Try adding cipherText[size] = '\0'; at the end of the loop to make sure the encoded string only contain the encoded data.

Answer 2

Initialize the cipherText before for loop using memset in your code like the following way.
memset(cipherText,0,sizeof(cipherText));
for (i = 0; i < size; i++)
{
//Convert the characters to an integer
PlainNums[i] = charInt(plaintext[i]);
//....
// rest of the code
You must need to include<string.h.
And it works.