Cannot input more than one string in palindrome program - c++

#include <iostream>
#include <ctype.h>
using namespace std;
void isPalindrome();
int main()
{
char response;
isPalindrome();
cout << "Input another string(y/n)?" << endl;
cin >> response;
response = toupper(response);
if (response == 'Y')
isPalindrome();
return 0;
}
void isPalindrome()
{
char str[80], str2[80];
int strlength;
int j = 0;
int front, back;
bool flag = 1;
cout << "Input a string:" << endl;
cin.getline(str, 80);
strlength = strlen(str);
for (int i = 0; i < strlength; i++)
{
if (islower(str[i]))
str[i] = toupper(str[i]);
}
for (int i = 0; i < strlength; i++)
{
if (isalpha(str[i]))
{
str2[j] = str[i];
j++;
}
}
str2[j] = '\0';
front = 0;
back = strlength - 1;
for (int i = 0; i < j / 2; i++)
{
if (str2[front] != str2[back])
{
flag = 0;
break;
}
}
if (!(flag))
cout << "It is not a palindrome" << endl;
else
cout << "It's a palindrome" << endl;
cout << "str: " << str << " str2: " << str2 << " strlength: " << strlength << " j: " << j << endl;
cout << "front: " << front << " back: " << back << " flag: " << flag << endl;
}
I was just wondering if anybody could help explain to me why my code isn't working.
I can run it once just fine and I get the right answer, but when the prompt asks if I want to input another string and I type 'y', the prompt just skips over the input and terminates on it's own.
I tried cin.ginore('\n', 80), but that just gave me a bunch of blank lines. I added the bit of code at the end to check the values and they all go to 0 and drop the strings.
Maybe a link to a proper explanation of how the system handles memory?
edit:
I keep getting the same problem when running the input sequence a second time. The output looks like this:
Input a string:
Radar
It's a palindrome
Input another string(y/n)?
y
_ <- this being my cursor after pressing enter 3 times
I'll just re-build the program from scratch and try to do it without a function. I'd still appreciate a link to a page that explains how to process user input using modern c++.

The problem is with:
cin >> response;
This reads the user input y/n into the variable response but a newline is left in the input buffer which is picked by the getline function the isPalindrome function.
To fix this you need to remove the newline from the input buffer after you read the user response. You do it by using:
cin >> response;
std::cin.ignore(INT_MAX);
With the above fix you can retry the palindrome check just once. To make multiple retries possible you'll need a loop. I would recommend a do-while loop in your main as:
char response;
do {
isPalindrome();
cout << "Input another string(y/n)?" << endl;
cin >> response;
std::cin.ignore(INT_MAX);
response = toupper(response);
} while(response == 'Y');

You need a loop. There's no code that instructs the program to go back to the top.
char response = 'Y';
while (response == 'Y') {
isPalendrome();
cout << "Input another string(y/n)?" << endl;
cin >> response;
}
This isn't your entire program, just key elements that you need for a while loop. You should get an understanding of how while works and make this work for your program.

In contemporary C++ one would typically use standard library components for string processing:
#include <iostream>
#include <string>
int main()
{
std::string line1, line2, response;
do
{
std::cout << "First string: ";
if (!std::getline(std::cin, line1)) { /* error */ }
std::cout << "Second string: ";
if (!std::getline(std::cin, line2)) { /* error */ }
// check line1 and line2 for palindromy
std::cout << "Again (y/n)? ";
std::getline(std::cin, response);
} while (std::cin && (response == "y" || response == "Y"));
}

Related

How to Accept [ENTER] key as an invalid input and send out error message

This is a program that grade user inputs for the questions of Driver's License Exam.
I'm having trouble of validating the user input.
I'd like to accept the [ENTER] key as an invalid input and proceed to my validation rather than just go to an empty line and cannot process to the next question. Purpose is to send out error message and that no input is given and [ENTER] key is not valid input and only accept one more chance to enter valid input which are a/A, b/B, c/C, or d/D. So that is why I'm using if statement here instead of loop.
I tried if (testTakerAnswers[ans] == (or =) '\n') {} but still doesn't solve the problem of newline.
I include curses.h in here hope to use getch() statement from the other post but somehow I can't manage to work in my code with an array instead of regular input.
I'm looking for other methods as well rather than getch()
So should I adjust my bool function, or directly validate input in main() function.
#include <iostream>
#include <iomanip>
#include <string>
#include <cctype>
#include <curses.h>
using namespace std;
const unsigned SIZE = 20; // Number of qns in the test
char testTakerAnswers[SIZE]; //Array to hold test taker's answers
bool validateInput(char);
class TestGrader
{
private:
char answers[SIZE]; // Holds the correct answers // Answer is array
int getNumWrong (char[]);
void missedQuestions (char[]);
public:
void setKey(string); // Initialize object with standard keys
void grade(char[]); // Grades the answers from tester
};
void TestGrader::setKey(string key){
if (key.length()!=SIZE){
cout << "Error in key data.\n";
return;
}
for (unsigned pos = 0; pos < SIZE ; pos ++)
answers [pos] = key [pos];
}
void TestGrader::grade(char test[])
{
int numWrong = getNumWrong(test);
if (numWrong <= 5)
cout << "Congratulations. You passed the exam.\n";
else
cout << "You did not pass the exam. \n";
cout << "You got " << (SIZE-numWrong) << " questions correct. \n";
if (numWrong > 0){
cout << "You missed the following " << numWrong << " questions: \n";
missedQuestions(test);
}
}
int TestGrader::getNumWrong(char test[])
{
int counter = 0;
for (int i = 0; i < SIZE; i++){
if (answers[i] != toupper(testTakerAnswers[i])){
counter++;
}
}
return counter;
}
void TestGrader::missedQuestions(char test[])
{
// cout << testTakerAnswers[i]; This is to print taker's answers
int counter = 0;
for (int i = 0; i < SIZE; i++){
if (answers[i] != toupper(testTakerAnswers[i])){
cout << "\n" << i + 1 << ". Correct answers: " << answers[i];
counter++;
}
}
}
bool validateInput(char ans){ // Only A, B, C, D valid input
if (toupper(ans)!='A' && toupper(ans)!= 'B' && toupper(ans)!='C' && toupper(ans)!= 'D'){
cout << "\n********************WARNING*******************\n";
cout << "Invalid input! Enter only a/A, b/B, c/C, or d/D\n";
return false;
}
if (testTakerAnswers[ans] == '\n'){
return false;
}
return true;
}
int main()
{
const int NUM_QUESTIONS = 20;
string name; //Test taker's name
char doAnother; //Control variable for main processing loop
TestGrader DMVexam; //Create a TestGrader object
DMVexam.setKey("BDAACABACDBCDADCCBDA");
do {
cout << "Applicant Name: ";
getline(cin,name);
cout << "Enter answer for " << name << ".\n";
cout << "Use only letters a/A, b/B, c/C, and d/D. \n\n";
for (int i = 0; i < NUM_QUESTIONS; i++){
// Input and validate it
do{
cout << "Q" << i+1 << ": ";
cin >> testTakerAnswers[i];
if (!validateInput(testTakerAnswers[i])){
cout << "You get one more chance to correct.\nOtherwise, it count as wrong answer.";
cout << "\n*********************************************";
cout << "\nRe-enter: ";
cin >> testTakerAnswers[i];
cout << '\n';
break;
}
}while(!validateInput(testTakerAnswers[i]));
}
//Call class function to grade the exam
cout << "Results for " << name << '\n';
DMVexam.grade(testTakerAnswers);
cout << "\nGrade another exam (Y/N)? ";
cin >> doAnother;
while (doAnother != 'Y' && doAnother != 'N' && doAnother != 'y' && doAnother != 'n'){
cout << doAnother << " is not a valid option. Try Again y/Y or n/N" << endl;
cin >> doAnother;}
cout << endl;
cin.ignore();
}while(doAnother != 'N' && doAnother != 'n');
return 0;
}
Your issue is cin >> testTakerAnswers[i]; cin is whitespace delimited, that means that any whitespace (including '\n') will be discarded. So testTakerAnswers[i] can never be '\n'.
I'm not sure exactly what you want to do, but possibly try
getline(cin,input_string);
then
input_string == "A" | input_string == "B" | ...
So if only the enter key is pressed, input_string will become "".

c++ input for-loop followed by another input

c++ Microsoft visual studio on a windows.
im very new to coding. currently going through Programming -- Principles and Practice Using C++ by Stroupstrup and I came across a difficulty. I am to create a "score chart" with vector name and vector score from the user input. I used for-loop to get the input. now I am to modify the program so that with 2nd input from the user I can search the list and "cout<<" the score for a person. the problem is the the program completely ignores the 2nd "cin>>" command.
I search online and could not find a reasonable answer to this problem. Is there any special interaction between a for-loop input being terminated and another input (not looped)
syntax:
#include "stdafx.h"
#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main()
{
vector<string> name;
vector<int> score;
string temp2;
int i;
for (string temp; cin >> temp >> i;) //input terminated with "Ctrl+Z"
name.push_back(temp), score.push_back(i);
for (int i = 0; i < name.size(); ++i) {
for (int j = i + 1; j < name.size(); ++j) {
if (name[i] == name[j]) {
name[j] = "error";
score[j] = 0;
}
}
}
for (int i = 0; i < name.size(); ++i) {
cout << name[i] << "------" << score[i] << "\n";
}
cout << "name"; //this line shows in the console
cin >> temp2; //but I cannot prompt the user to input again?
return 0;
}
CTRL-Z is interpreted as "End-Of-File", such that any subsequent access to this stream will not read in items any more. The only secure way is to change program logic such that the list of names is terminated by, let's say "END", and not a CTRL-Z. Then you can continue in a save manner.
Often input from a terminal is read in line by line and parsed afterwards. This makes error handling easier. See the following code following such an approach:
#include <sstream>
int main() {
string line;
map<string,int> scoreboard;
cout << "enter name score (type END to finish):" << endl;
while (std::getline(cin, line) && line != "END") {
stringstream ss(line);
string name;
int score;
if (ss >> name >> score) {
scoreboard[name] = score;
} else {
cout << "invalid input. Type END to finish" << endl;
}
}
cout << "enter name:" << endl;
string name;
if (cin >> name) {
auto item = scoreboard.find(name);
if (item != scoreboard.end()){
cout << "score of " << name << ":" << item->second << endl;
}
else {
cout << "no entry for " << name << "." << endl;
}
}
}

Check letters against the word of an arbitrary size in a Hangman game

Currently I am working on a hangman game, I had previously coded it to only work for a 5 letter word, but now would like to make it handle any length of word, how could I change this code to make it work how I want it to?
#include "stdafx.h"
#include <iostream>
#include <string>
#include <stdlib.h>
#include <cstdlib>
using namespace std;
int main()
{
string word;
int tries;
string guess;
string wordguess;
string output;
cout << "Enter a word for player two to guess: ";
cin >> word;
system("CLS");
cout.flush();
cout << "Guess the word!" << endl;
for (int i = 0; i < word.length(); i++)
{
cout << "_ ";
}
cout << "Enter a letter: ";
cin >> guess;
for (int tries = 5; tries > 0; tries--)
{
if (guess[0] == word[0]) {
output[0] = word[0];
cout << "You guessed the first letter! Good job!" << endl;
}
if (guess[0] == word[1]) {
output[2] = word[1];
cout << "You guessed the second letter! Good job!" << endl;
}
if (guess[0] == word[2]) {
output[4] = word[2];
cout << "You guessed the third letter! Good job!" << endl;
}
if (guess[0] == word[3]) {
output[6] = word[3];
cout << "You guessed the fourth letter! Good job!" << endl;
}
if (guess[0] == word[4]) {
output[8] = word[4];
cout << "You guessed the fifth letter! Good job!" << endl;
}
cout << output << endl;
cout << "You have " << tries << " tries left. Take a guess at the word: " << endl;
cin >> wordguess;
if (wordguess == word)
{
cout << "Congratulations, you guessed the word correctly!" << endl;
break;
}
}
system("pause");
return 0;
}
As you can tell I was checking each position from 0 to 4 (first through fifth letter). I know there are plenty of ways that I could have coded this better but as you can guess, I am new to coding and this is the way I thought of it. Please note this is still a work in progress so it is not fully complete. Any help would be great!
When designing an algorithm, think of how you would do this by hand, without a computer. Then let the code do the same.
If you were checking your friend's guess against a word written on sand, you would probably go about it like this:
go through the written pattern character by character, pronouncing your word in memory
for each letter, check if it is equal to the guess
if it is
replace the placeholder with it
memorize that your friend guessed right.
Also note if there are any placeholders left
if there aren't, your friend wins
finally, if your friend didn't guess right, score them a penalty point and check if they lose
Now, all that leaves is to put this down in C++. The language provides all sorts of entities - let's check which ones fit ours needs the best:
the word and the current pattern - strings of a fixed size
bits to memorize:
whether the current guess is right - bool
placeholders left - int
penalty points (or, equivalently, attempts left) - int
parts of the algorithm:
looping over a string - for loop of one of a few kinds
we need to replace the character in the pattern at the same index as the guessed letter in the word. So, we need to have the index when looping. Thus the flavor with the index variable, for(std::string::size_type i = 0; i < str.size(); ++i) probably fits the best.
// Example program
#include <iostream>
#include <string>
using namespace std;
class my_game
{
private:
string congrats_array[15] = {"first", "second", "third", "fourth", "fifth", "sixth", "seventh", "eighth", "nineth", "tenth", "eleventh", "twelfth", "thirteenth", "fourteenth", "fifteenth"};
string word_to_guess;
int tries_left;
int word_length;
int letters_guessed_count;
string guessed_letters;
void check_letter(char letter);
void print_current_word_state();
public:
my_game();
void begin_the_game();
void play_the_game();
};
my_game::my_game()
{
}
void my_game::begin_the_game()
{
cout << "Enter a word for player to guess: " << endl;
cin >> word_to_guess;
system("CLS");
cout.flush();
cout << "Enter the tries amount!\n" << endl;
cin >> tries_left;
word_length = word_to_guess.size();
guessed_letters = "_";
letters_guessed_count = 0;
for(int i = 0; i < word_length - 1; i++){
guessed_letters += "_";
}
}
void my_game::play_the_game()
{
cout << "Guess the word!" << endl;
char letter;
for(int i = 0; i < tries_left; i++)
{
cout << guessed_letters << endl;
cout << "Enter a letter: " << endl;
cin >> letter;
check_letter(letter);
if(letters_guessed_count == word_length){
cout << "Congrats! You won!" << endl;
return;
}
}
cout << "You lose" << endl;
}
void my_game::check_letter(char letter)
{
for(int i = 0; i < word_length; i++)
{
if(word_to_guess[i] == letter && guessed_letters[i] != letter)
{
guessed_letters[i] = letter;
letters_guessed_count++;
cout << "You guessed the" << congrats_array[i] <<"letter! Good job!" << endl;
}
}
}
int main()
{
my_game game;
game.begin_the_game();
game.play_the_game();
}
So, in short what you need to do this with words of any arbitrary length is to use string's .substr() function and the stringstream library's .str() and << and >> operators. This version of your code uses a function that inserts a correctly guessed character at the appropriate indexed location. This will gradually replace the "_________" with letters at the correct places. This is much easier to do in Java, but stringstream is a good library I would highly recommend getting familiar with it. I'll leave the problem of how to handle multiple instances of a guessed character up to you (ie 'i' in "bibliography")
#include <string>
using std::string;
#include <sstream>
using std::stringstream;
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
string newString(string, int, string);
int main()
{
string word;
string guess;
int tries;
string output;
string input;
cout << "Enter word for player 2 to guess: ";
cin >> word;
stringstream ss;
//---------- fills the stream with "_"s matching the length of word
for(int i = 0; i < word.length(); i++)
ss << "_";
//----------- assigns the initial value of "___..." to output
ss >> output;
//----------- sets up the loop
tries = 5;
bool found = false;
for(int i = 0; i < 5; i++)
{
cout << "\nTry " << i << " of 5: Enter a letter or guess the word: ";
cin >> input;
if(input == word)
{
cout << "Congratulations, you guessed the word correctly!" << endl;
break;
}
//------------------ else, proceed with replacing letters
if(word.find(input) != std::string::npos)
{
size_t position = word.find(input); // finds index of first instance of the guessed letter
cout << "You guessed the " << position+1 << " letter! Good job!" << endl; // since strings start at index 0, position+1
//------- replaces appropriate "_" with the guessed letter
output = newString(input, position, output);
cout << "\n" << output;
// Around here you'll want to set up a way to deal with multiple instances
// of the same letter
}
else
cout << "Incorrect guess" << endl;
}
return 0;
}
//---------------------------------------------------
string newString(string guess, int index, string word)
{
string NewString;
stringstream temp;
//---------- hack up the string into sections before and after the index
string before = word.substr(0, index);
string after = word.substr(index+1, word.length() - index+1);
//---------------- populates the new stringstream and assigns it to the result
temp << before << guess << after;
NewString = temp.str();
return NewString;
}

"cin.ignore" hit enter twice to continue

I have the following code in a for loop. When it goes through for the first time, it runs great. However, when it gets run again, it stops just before the cin.ignore, and I have to hit the enter key before I can type my input. Any reason why that is? Thanks.
cin.ignore(100, '\n');
string input;
getline(cin, input);
EDIT:
Here is the entire part of the code:
Note that the vector restaurants has 16 strings in it. And the function ifOddNumberOfRestaurants is the following:
void ifOddNumberOfRestaurants(vector<string> restaurants){
cout << "To begin the tournament, please add one more restaurant to the list: ";
cin.ignore(1000, '\n');
string newRestaurant;
getline(cin, newRestaurant);
restaurants.push_back(newRestaurant);
}
The code with problems:
else if ( option == 5 ) {
int numberRestaurants = restaurants.size();
int evenOrOdd = numberRestaurants % 2;
if (evenOrOdd == 1){
ifOddNumberOfRestaurants(restaurants);
}
vector<string> battleRestaurants(restaurants);
int stop = 0;
while ( stop == 0 ){
double half = battleRestaurants.size()/2;
int option1 = 0;
int option2 = 1;
int match = 1;
for(int i = 0; i < half; i++){
cout << "Match " << match << "/" << half << " --- " << battleRestaurants[option1] << " *OR* " << battleRestaurants[option2] << "? ";
match++;
cout << "\nBEFORE IGNORE\n";
cin.ignore(100, '\n');
cout << "\nAFTER IGNORE\n";
string winner;
getline(cin, winner);
if ( winner == battleRestaurants[option1]){
battleRestaurants.erase(battleRestaurants.begin() + option2);
}
else if ( winner == battleRestaurants[option2]){
battleRestaurants.erase(battleRestaurants.begin() + option1);
}
option1++;
option2++;
cout << "Postion of i: " << i << "\nPosition of Option 1: " << option1 << "\nPosition of Option 2: " << option2 << "\n" << endl;
printRestaurants(battleRestaurants);
}
}
}
I Think your problem is that you have the cin.ignore(100, '\n'); When you do not need it remove that and your code should work ok. I tried just a little snippet of that part and it worked fine. EX: `vector restaurants;
int numberRestaurants = restaurants.size();
int evenOrOdd = numberRestaurants % 2;
for (int i = 0; i < 5; i++)
{
if (evenOrOdd == 1){
cout << "To begin the tournament, please add one more restaurant to the list: ";
//cin.ignore(100, '\n');
string newRestaurant;
getline(cin, newRestaurant);
restaurants.push_back(newRestaurant);
}
}
Remove the ignore thats why you have to push enter before it accepts anything else because it will ignore the first 100 chars or a new line whichever comes first.

Do While loop breaks after incorrect input?

I am trying to have a loop continue to prompt the user for an option. When I get a string of characters instead of an int, the program loops indefinitely. I have tried setting the variable result to NULL, clearing the input stream, and have enclosed in try{}catch blocks (not in this example). Can anyone explain to me why this is?
#include <iostream>
#include <vector>
#include <string>
using namespace std;
int menu(string question, vector<string> options)
{
int result;
cout << question << endl;
for(int i = 0; i < options.size(); i++)
{
cout << '[' << i << ']' << options[i] << endl;
}
bool ans = false;
do
{
cin >> result;
cin.ignore(1000, 10);
if (result < options.size() )
{
ans = true;
}
else
{
cout << "You must enter a valid option." << endl;
result = NULL;
ans = false;
}
}
while(!ans);
return result;
}
int main()
{
string menuQuestion = "Welcome to my game. What would you like to do?";
vector<string> mainMenu;
mainMenu.push_back("Play Game");
mainMenu.push_back("Load Game");
mainMenu.push_back("About");
mainMenu.push_back("Exit");
int result = menu(menuQuestion, mainMenu);
cout << "You entered: " << result << endl;
return 0;
}
It looks like there is a random element here, since result is not initialized.
In any case, test cin directly
if ( cin && result < options.size() )
and reset it upon invalid input so it will again perform I/O operations
result = 0; // inappropriate to initialize an integer with NULL
cin.clear(); // reset cin to work again
cin.ignore(1000, '\n'); // use \n instead of ASCII code