null terminated char array (c-string) not printing without for loop - c++

Question

**I can't use vectors, or any functions from the standard library with this program. Hence why I am writing it all myself.
Alright, this program is just about finished. All my user defined functions are working fine, except for the reverseCString function. When I run the program, and enter a string of "hello", I can select menu option "rev" to reverse the string. My main function then calls the reverseCString function, and uses the for loop in my main to print out my reversed c-string. The program works fine at this point, until the do-while loop continues..
After the rv function is called though, the program loops to continue to allow the user to modify their string, as it should. However, my c-string vanishes at this point. I can still operate on it if I use the other commands/funtions, but the c-string doesn't print to cout.
I don't understnad what is causing this, but I have isolated the problem down to the reverseCString function.
Here is my code so far:
#include<iostream>
#include<stdlib.h>
#include<cstring>
#include<string>
#include<math.h>
using namespace std;
void shiftLeft(char szString[], size_t shiftBy)
{
const char *p = szString;//
while (*p) ++p;//advance p to point to the the null terminator, found via personal research at http://stackoverflow.com/questions/12201815/what-difference-between-whilepp-while-p-and-whilep
size_t len = p - szString;//len is set to the size of our c-string
if (len > 1 && (shiftBy %= len))
{
char *ends[] = { szString+shiftBy, szString+len, szString+(len - shiftBy) };//create a temporary array for storage
for (size_t i = 0; i < 3; ++i)//use a for loop to flip the first three character
{
char *start = szString, *end = ends[i];
while (start < --end)//now flip the rest of the characters
{
char ch = *start;
*start++ = *end;
*end = ch;
}
}
}
}
void shiftRight (char szString[], int size, int shiftBy)
{
if(shiftBy > size){
shiftBy = shiftBy - size;
}
if(size == 1){
//do nothing, exit function with no change made to myarray
}
else{
char temp;
//for loop to print the array with indexes moved up (to the right) --> by 2
for (int i=0; i < size; i++)
{//EXAMPLE shift by 3 for a c-string of 5
temp = szString[size-shiftBy];//temp = myarray[2]
szString[size-shiftBy] = szString[i];//myarray[2] = myarray[i]
szString[i] = temp;//myarray[i] = temp(value previously at index 2)
}
}
}
void reverseCString(char szString[], const size_t& size){
char temp;
int i = 0;
int j = size-1;
//we can use a simple tep variable to flip everything
while(i < j)
{
temp = szString[i];
szString[i] = szString[j];
szString[j] = temp;
i++;
j--;
}
}
int main(){
string repeat = "";
string userInputString;
cout << "Please eneter your string: " << endl;
//cin >> ws;
getline(cin,userInputString);
char * szString = new char [userInputString.length()+1];
strcpy (szString, userInputString.c_str());
do {
cout << "Your c-string is: " << szString << endl;
string commandString = "";
cout << "Please enter a command: ";
getline(cin,commandString);
if (commandString[0] == 'L'){
cout << "You have chosen to shift your string left by " << commandString[1] << " characters." << endl;
const char * shiftLeftPtr = &commandString[1];
//convert this value to an int for our function
int shiftLeftBy = atoi(shiftLeftPtr);
//run our shifleft function
shiftLeft(szString,shiftLeftBy);
//print the results
cout << "Your c-string, shifted left by " << commandString[1] << endl;
cout << szString;
}
if (commandString[0] == 'R'){
cout << "You have chosen to shift your string right by " << commandString[1] << " characters." << endl;
const char * shiftRightPtr = &commandString[1];
//convert this value to an int for our function
int shiftRightBy = atoi(shiftRightPtr);
//run our shiftright function
shiftRight(szString,userInputString.length(),shiftRightBy);
//print the results
cout << "Your c-string, shifted right by " << commandString[1] << endl;
cout << szString;
}
if (commandString.compare("rev") == 0){
cout << "You have chosen to reverse your string. " << endl;
//run our reverseArray function
reverseCString(szString,userInputString.length()+1);
cout << "Your c-string, reversed: ";
for(int i = 0; i < userInputString.length()+1; i++){
///////////////////////////right her seems to be my issue
cout << szString[i];
}
}
if (!(commandString[0] == 'R' || commandString[0] == 'L' || commandString.compare("rev") == 0)){
cout << "You have entered an invalid selection." << endl;
}
cout << "\nEnter 'quit' to close the program, anything else to continue: ";
getline(cin,repeat);
}while(repeat.compare("quit") != 0);
return 0;
}

Answer 1

Your length logic is broken. Say the string contains "bar\0". You do this:
reverseCString(szString,userInputString.length()+1);
Now, length is 3, and you pass 4 to reverseCString. Then this happens:
void reverseCString(char szString[], const size_t& size){
char temp;
int i = 0;
int j = size-1;
Now, i is 0 and j is 3. So you swap items 0 and 3. Well, what are the items?
0 = b
1 = a
2 = r
3 = \0
When you swap items 0 and 3, you create a string that starts with a terminator, "\0rab". Of course printing that out won't produce anything.