I'm having an issue where I'm designing a palindrome checker. I have no problem with single words ("noon", "2002", etc.), but every time when I type in a phrase that has multiple words with spaces (such as "laminate pet animal"), my program loses its mind and goes into an infinite loop. Perhaps it has something to do with the checks (Make sure the string isn't NULL or greater than 80 characters) I put inside? I've been step by step debugging with no success. I think it has something to do with how the string is stored in memory, but I can't place it exactly.
//Preprocessor directives
#include <iostream>
#include <cstdlib>
#include <string>
#include <iterator>
#include <vector>
#include <stdlib.h>
using namespace std;
//Function declarations
string input();
bool check(string a);
int main()
{
//Repeater variable
bool rep = 1;
bool result = 0;
//Declares string to be checked
string palin;
while (rep == 1)
{
//Creates string and calls input function
palin = input();
//Close function if stopped midway
if (palin == "2")
return 0;
result = check(palin);
//Displays the results
if (result == 1)
cout << palin << " is a palindrome." << endl;
else
cout << palin << " is not a palindrome." << endl;
//Ask if the user wants to enter another Palindrome
cout << "Continue? (1 for yes, 0 for no): ";
cin >> rep;
}
cout << "Closing program..." << endl;
system("pause");
return 0;
}
string input()
{
//Asks for and receives input string
string temp;
cout << "Please enter a string (type zero or 0 to quit): ";
cin >> temp;
//Close program if user enters 0 or zero
if (temp == "0" || temp == "zero")
{
cout << "Exiting program..." << endl;
system("pause");
return "2";
}
//Check if string is null, then ask for input again
if (temp.empty())
{
cout << "There is nothing entered. Please enter a string: ";
cin >> temp;
}
//Check if string is too long, ask for input again
if (temp.length() >= 80)
{
while (temp.length() > 80)
{
cout << "The string is too long. Please enter a smaller string: ";
cin >> temp;
}
}
return temp;
}
bool check(string a)
{
//Creates 2 iterators that traverse the string
string::iterator test1;
string::reverse_iterator test2;
test1 = a.begin();
test2 = a.rbegin();
//Continue until the end of either side of the string
while (test1 != a.end() && test2 != a.rend())
{
//Check if the current symbol is alphanumeric
while (test2 != a.rend() && !isalnum(*test2))
++test2;
while (test1 != a.end() && !isalnum(*test1))
++test1;
//Break loop when you hit the end
if (test1 == a.end() || test2 == a.rend())
break;
//If they're not the same it's not a palindrome, exit function
if (tolower(*test1) != tolower(*test2))
return 0;
++test1;
++test2;
}
return 1;
}
std::cin's >> operator only reads up to the next whitespace character. If you want to read the entire line, use std::getline().
cin >> temp; //reads until the next whitespace
getline(cin, temp); //reads until the next newline character
What was happening was that the first read operation after you enter "race car" would read "race" and then leave "car" in the stream, then the next read operation would read "car", resulting in unexpected behavior since your code was expecting a 1 or 0.
This is unrelated to your problem, but it's usually good form to not use using namespace std. There's a variety of reasons, but the most basic one is if you write your own function called getline(), you'll run into problems.