Help with a rot13 encrypter

[jgelderloos]

im working on an encryption program and i need some help. so far it words fine except when i enter a space. when this happens it seems to end the loop and spit out the first word. any help would be great

#include <iostream>
#include <string>
using namespace std;


string rot13(string input)
{
	int intVal = 0;
	int length = input.size();
	int charPosition = 0;
	string finalText = "";
	string character;
	
	while(charPosition != (length + 1))
	{

		if(input[charPosition] >= 'A' && input[charPosition] <= 'M')
		{
			intVal = input[charPosition] + 13;
			character = char(intVal);
			finalText = finalText + character;
		}
	
		if(input[charPosition] >= 'a' && input[charPosition] <= 'm')
		{
			intVal = input[charPosition] + 13;
			character = char(intVal);
			finalText = finalText + character;
		}
	
		if(input[charPosition] >= 'N' && input[charPosition] <= 'Z')
		{
			intVal = input[charPosition] - 13;
			character = char(intVal);
			finalText = finalText + character;
		}
	
		if(input[charPosition] >= 'n' && input[charPosition] <= 'z')
		{
			intVal = input[charPosition] - 13;
			character = char(intVal);
			finalText = finalText + character;
		}

		if(input[charPosition] >= ' ' && input[charPosition] <= '@')
		{
			intVal = input[charPosition] + 0;
			character = char(intVal);
			finalText = finalText + character;
		}

		charPosition = charPosition + 1;
	
	}

	return finalText;

}

[vmanes]

How are you reading in the input string? If you use cin >> str; all you're going to get is one word of input.

Use getline( cin, str ); to read in multiple word strings.

Also, your loop control while(charPosition != (length + 1)) is an OBO situation.

[jgelderloos]

thanks it works alot better now but what do you obo situation and what would be a better way of controlling it?

[vmanes]

Length of string is count of the characters in it. For example "string" has length 6. The last character position you can access is at index 5 - counting starts at 0 and goes to length-1. You start correctly, but your code (attempts) to process one character past the end of the actual string content.
If you were using C-style (char array based) strings, that one char too far would be the NULL ( '\0', value 0). In a C++ string, that position is not defined to hold any value. In practice, I find most compilers put a NULL after the last valid character, but you can't count on that.

A more common way to write that loop would be while(charPosition < length ) FYI: OBO means Off By One

[cikara21]

//....
if(isspace(input[charPosition]))
//--or input[charPosition] == char(/*decimal number for space*/) 
&& input[charPosition] <= '@')
		{
			intVal = input[charPosition] + 0;
			character = char(intVal);
			finalText = finalText + character;
		}
//....

[ArkM]

Use else if instead of several ifs in the loop. Why you check redundant conditions after if (... true ...)?

[cikara21]

thanks...

//....
      if(isspace(input[charPosition])
      //--or input[charPosition] == char(/*decimal number for space*/)
      && input[charPosition] <= '@')
      {
      intVal = input[charPosition] + 0;
      character = char(intVal);
      finalText = finalText + character;
      }
      //....