caesar encryption in C with undefined input - c

Question

iam trying to write a simple caesar program in C.
The input i want to give should be with undefined lenght like in the program.
The problem i have is, when i enter a short string like "HELLO WORLD" in the encrypted string i have some random additions at the end.
When i give a longer string as input the program crashes befor it starts to encrypt.
I have no idea where the problem could be, maybe some of you can give me a hand or have ideas what is crap here :/
Every advice is welcome thank you :)
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
// realloc the size of memory for the user input
char *inputString(FILE *fp, size_t size)
{
// the size is extendet by the input with the value of the provisional
char *str;
int ch = 0;
size_t len = 0;
str = realloc(NULL, sizeof(char)*size); // size is start size
if(!str)
return str;
while(EOF != (ch = fgetc(fp)) && ch != '\n')
{
str[len++] = ch;
if(len == size)
{
str = realloc(str, sizeof(char)*(size += 16));
if(!str)
return str;
}
}
str[len++] = '\0';
return realloc(str, sizeof(char)*len);
}
// lowercase letters
void makeLowerCase(char *input)
{
while(*input != '\0') // "while(*input)" would also work
{
*input = tolower(*input);
input++;
}
}
// test function
// character length of the input
int lengthOfInput(char *input)
{
int len = 0;
while(*input != '\0') // "while(*input)" would also work
{
len++;
input++;
}
return len;
}
// encrypts the input caesar
char *encrypt(char *toBeEncrypted, int caesarNum)
{
int tmp = 0; // going through the input
char *tbE;
for(;*toBeEncrypted != '\0'; toBeEncrypted++, tmp++)
{
*(tbE+tmp) = *toBeEncrypted + caesarNum;
printf("%c", *(tbE+tmp));
}
return tbE;
}
// ------------------------------------------------------
// main
// ------------------------------------------------------
int main(void)
{
char *s; // input from user
char *encryptedString; // encrypted input/output
int loi = 0; // length of input
srand((unsigned)time(NULL)); // initialize random value for encryption
int caesar = (rand()%25) + 1; // random number for caesar encryption
printf("input string : ");
s = inputString(stdin, 10); // realloc the memory space for the input
makeLowerCase(s); // convert to lower case
printf("lower case: %s\n",s);
loi = lengthOfInput(s); // length of the input
printf("lenght of input: %d\n",loi);
printf("caesar number: %d\n",caesar);
encryptedString = encrypt(s, caesar); // encryption
printf("\nencrypted : %s",encryptedString); // output
free(s);
free(encryptedString); // free the memory
return 0;
}

Answer 1

You are using an uninitialized variable.
// encrypts the input caesar
char *encrypt(char *toBeEncrypted, int caesarNum)
{
int tmp = 0; // going through the input
char *tbE;
for(;*toBeEncrypted != '\0'; toBeEncrypted++, tmp++)
{
*(tbE+tmp) = *toBeEncrypted + caesarNum;
// ^
// ^ here tbE is used, but it has never been initialized
//
printf("%c", *(tbE+tmp));
}
return tbE;
}
There may be more issues.
Side note
In encrypt the loop should be written with array indexes rather than with pointer arithmetic for the sake of readability:
for(i = 0; toBeEncrypted[i] != '\0'; i++)
{
tbE[i] = toBeEncrypted[i] + caesarNum;
printf("%c", tbE[i]);
}