Question

Palindrome Detector C++

A palindrome is any word, phrase, or sentence that reads the same forward and backward. Here are some well-known palindromes:

Able was I, ere I saw Elba
A man, a plan, a canal, Panama
Desserts, I stressed
Kayak

Write a program that determine whether an input string is a palindrome or not.

Input:

The program should prompt the user "Please enter a string to test for palindrome or type QUIT to exit: " and then wait for the user input. The user can type a single line of input and hit enter. The input can contain any characters, including uppercase and lowercase letters, digits, special symbols, spaces, etc. The program will check the input against the palindrome properties, will display the result, and ask for an input again. The user can check multiple lines before deciding to exit the program. The user can type quit/QUIT/Quit or any combination of uppercase/lowercase letters in quit and exit the program immediately.

Output:

There are two possible outputs from the program:

If the input string is a palindrome, then the program will display "The input is a palindrome."

If the input string is not a palindrome, then the program will display "The input is not a palindrome."

Programming instructions:

Follow these instructions as closely as possible. They will help you in coming up with the right solution. Deviations from requirements (indicated with asterisks) will result in penalties.

1. Declare the input string to be 100 characters maximum. Some of the input strings are quite long.
2. Make sure to compare the user input against the word "QUIT" before taking additional steps. The comparison should be case insensitive. Use function strcasecmp() or something similar for case insensitive comparison (you'll need to include string.h header file on Linux/Unix).
3. (*) Your program should declare and make use of exactly one stack and one queue. The stack and the queue should store single characters as elements. Do NOT use <stack> and <queue> headers
4. (*) Read the input string and load alpha characters into the stack and into the queue at the same time (ignore all the other characters that are not letters). Convert the letters to lowercase or to uppercase before loading onto the stack or into the queue. This will simplify the further comparison.
5. (*) Your program should contain one boolean function, called isPalindrome, which accepts one stack and one queue as an input and determines whether their contents are matching or not.
6. After each iteration and at the beginning of each iteration, the stack and the queue should be completely empty.
7. (*) You should allow the user to enter strings containing spaces. I recommend that you use cin.getline function to read the input.

Answer 1

C++ Program:

/* C++ Program that reads in a string and determines whether it is palindrome or not */

#include <iostream>

using namespace std;

//Function prototype
bool isAPalindrome(char[], int, int);

//Main function
int main()
{
char str[256];
int length;

//Reading a string
cout << "\n Please enter a string to test for palindrome or type QUIT to exit: ";
cin.getline(str, 256);

//Loop till user want's to quit
while(strcmp(str, "QUIT") != 0)
{
//Find out the length
length = strlen(str);

//Call the function and check whether given string is palindrome or not
if(isAPalindrome(str, 0, length-1))
cout << "\n " << str << " is a palindrome.";
else
cout << "\n " << str << " is not a palindrome.";

//Reading string again
cout << "\n\n Please enter a string to test for palindrome or type QUIT to exit: ";
cin.getline(str, 256);
}

cout << endl;
return 0;
}

//Function that checks whether given string is palindrome or not
bool isAPalindrome(char str[], int lowerBound, int upperBound)
{
char ch1,ch2;

//Checking for boundary crossings
if(lowerBound > upperBound)
return true;

//Escaping white spaces and punctuation marks
while(lowerBound <= upperBound)
{
//Checking for punctuation and spaces
if(ispunct(str[lowerBound]) || isspace(str[lowerBound]))
lowerBound ++;
else
break;
}

//Escaping white spaces and punctuation marks
while(upperBound >= lowerBound)
{
//Checking for punctuation and spaces
if(ispunct(str[upperBound]) || isspace(str[upperBound]))
upperBound --;
else
break;
}

//Getting two characters in upper case
ch1 = str[lowerBound];
ch1 = toupper(ch1);

ch2 = str[upperBound];
ch2 = toupper(ch2);

//Comparing characters
if(ch1 != ch2)
return false;

//Incrementing lower bound
lowerBound++;

//Decrementing upper bound
upperBound--;

//Recursive call
return isAPalindrome(str, lowerBound, upperBound);
}
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Sample Run: