Guess the number - Infinite loop when bad read - c++

So I am making this Guess the number game in c++ that looks like this:
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int main()
{
srand(time(0));
int secretNumber = rand() % 100 + 1; //Generate "Random number"
int nbrOfGuesses = 0;
int userInput;
cout<<"\t************************************"<<endl;
cout<<"\t* *"<<endl;
cout<<"\t* Guess the number! *"<<endl;
cout<<"\t* *"<<endl;
cout<<"\t************************************"<<endl;
cout<<endl;
cout << "Try to find the secret int number: " << endl;
//While input is good
while(cin.good())
{
//Do this
do {
cin>>userInput;
nbrOfGuesses++;
if (userInput>secretNumber)
cout << "Smaller!\n";
else if(userInput<secretNumber)
cout << "Bigger!\n"; // <-- Infinite loop here when you enter something other than an integer
else //Also using this as a backup of (cin.good())
cout << "Something went wrong with the read";
break;
} while(userInput!=secretNumber);
cout << "\nCongratulations! You got it in " << nbrOfGuesses << " guesses\n";
}
system("pause");
return 0;
}
*Sorry if the code is note very elegant
As you can see, the code works great until you enter a random caracter like '&' or 'j' or anything else that isn't an integer...Then it loops at cout<<"Bigger!";
So my question is: What is causing this?

Check this post, it is about the same problem. To summarize:
cin>>userInput;
if (cin.fail()) {
cout<<"Invalid Entry, please try again."<<endl;
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
}
Thanks ildjarn for pointing the missing ignore statement, I missed that part even though its clearly mentioned in the post I linked to!!

See this FAQ: How can I get std::cin to skip invalid input characters?

cin>>userInput;
If it cannot read an integet, the bad bit is set for the cin stream.
You should check and clear afterwords.
if ( cin.fail() )
{
cin.clear();
try again
}

Related

For Loops (C++)

Assignment:
The program should ask the user to enter a positive number and display all numbers from 1 to the input value. If the number is not positive, an error message should show up asking the user to re - enter the number.
My specific problem:
For my program, if the user enters an incorrect number and then re - enters a positive number, it does not display all the numbers from 1 to the input value. The program just ends.
#include <iostream>
using namespace std;
int main()
{
int userChoice;
int i = 1;
cout << "Enter a positive integer" << endl;
cin >> userChoice;
if (userChoice > 0)
{
for (i = 1; i <= userChoice; i++)
{
cout << "Loop 1:" << endl;
cout << i << endl;
}
}
else if (userChoice < 0)
cout << "Please re - enter" << endl;
cin >> userChoice;
system("pause");
return 0;
}
You need some sort of loop at the top of your program, that keeps asking for input until the user provides something valid. It looks like a homework assignment, so I will provide pseudo-code, not something exact:
std::cout << "Enter a number:\n";
std::cin >> choice;
while (choice wasn't valid) { // 1
tell the user something went wrong // 2
ask again for input in basically the same way as above // 3
}
// after this, go ahead with your for loop
It is actually possible to avoid the duplication here for step 3, but I worry that might be a little confusing for you, so one duplicated line really isn't such a big problem.
As an aside, you may wish to reconsider your use of what are often considered bad practices: using namespace std; and endl. (Disclaimer - these are opinions, not hard facts).

how to allow multiple inputs in case of an incorrect data type entry in cpp?

I have a program which generates random number and asks user to keep guessing it until he/she gets it right. I want it to keep accepting new values even if i incorrectly enter any other data type by handling the error cases.
My problem is that when i am trying to run the below program, as soon i input a character and hit enter, it goes into an infinite loop. I tried using cin.ignore() and cin.clear() but that just makes the program stop after the first entry.
Can anyone please help me understand what is going on and how to achieve the desired output? Thanks in advance.
#include <iostream>
#include <cstdlib>
#include <time.h>
using namespace std;
int main()
{
int secret_num, guess;
srand(time(NULL));
secret_num=rand() % 101 + 0;
cout<<"Enter your guess between 0 and 100: ";
do
{
if(!(cin>>guess))
{
cout<<" The entered value is not an integer"<<endl;
}
else if( isnumber(guess))
{
if(guess>secret_num)
cout<<"Too high";
else if(guess<secret_num)
cout<<"too low";
cout<<endl;
}
}
while(secret_num!=guess);
if((guess==secret_num)| (isnumber(guess)))
{
cout<<"yes the correct number is "<<secret_num<<endl;
}
return 0;
}
Edit: Here is a screenshot of what the output looks like with cin.clear() and cin.ignore(1000,'\n') in my code, when i enter a number after entering character twice.
if (!(cin >> guess))
{
cout << " The entered value is not an integer" << endl;
cin.clear(); // clear must go before ignore
// Otherwise ignore will fail (because the stream is still in a bad state)
cin.ignore(std::numeric_limits<int>::max(), '\n');
}
By default cin.ignore will ignore a single character. If they type more than 1 char, it won't be enough, that's why I've modified it a bit.
if ((guess == secret_num) | (isnumber(guess)))
| is a bitwise operator [OR]
|| is the logical operator [OR]
But I think what you actually want is && (AND)
if ((guess == secret_num) && (isnumber(guess)))
There're several problems.
You should use cin.clear() and cin.ignore() as #José suggested.
What's isnumber()? I guess it's returning false so no hint message (i.e. "Too high" and "too low") is printed out, looks like it stops although it's just waiting the next input. And isnumber() doesn't make sense to me. guess has been declared as an int, it has to be a number, doesn't it?
if((guess==secret_num)| (isnumber(guess))) is unnecessary here. The loop won't end until the user input the correct number, this condition should have been statisfied.
You can use clear and flush
if(!(cin>>guess))
{
cout<<" The entered value is not an integer"<<endl;
cin.clear();
fflush(stdin);
}
This works if you are reading from console. Otherwise you can go with #José answer.
I would change the logic inside your loop as there are some useless tests. This works for me:
#include <iostream>
#include <limits>
#include <cstdlib> // You may take a look at <random> and <chrono>
#include <time.h>
using std::cout;
using std::cin;
int main() {
srand(time(NULL));
int secret_num = rand() % 101;
cout << secret_num << '\n';
cout << "Enter your guess between 0 and 100:\n";
int guess = -1;
do {
cin >> guess;
if ( cin.eof() )
break;
if ( cin.fail() ) {
cout << "The entered value is not an integer, please retry.\n";
// clear the error flag
cin.clear();
// ignore the rest of the line
cin.ignore(std::numeric_limits<int>::max(),'\n');
// clear the value of the variable
guess = -1;
continue;
}
// now we know that guess is a number
if ( guess > secret_num )
cout << "Too high\n";
else if ( guess < secret_num )
cout << "Too low\n";
else {
cout << "Yes the correct number is " << secret_num << std::endl;
break;
}
} while ( true );
return 0;
}

How to ask for Age and set everything else as invalid?

I'm trying to set a basic program that asks for Age, And if the Number entered by the user is less than 99, It will say "Perfect". If the number is MORE than 99, it will say "You Can't be that old, Try again". Additionally, if the user enters something that is not a number (like a letter "m, r" or anything else like "icehfjc") then it will say "That is not a number."
This is my code so far:
#include <iostream>
#include <string>
using namespace std;
int main()
{
int age;
backtoage:
cout << "How old are you?\n";
cin >> age;
if (age < 99)
{
cout << "Perfect!\n";
system("pause");
}
if (age > 99)
{
cout << "You can't be that old, Try again.\n";
system("pause");
system("cls");
goto backtoage;
}
Else
{
cout << "That is not a number, Please Enter a Valid Number\n";
system("pause");
system("cls");
goto backtoage;
}
}
I know "Else" doesn't work because C++ treats letters as integers as well, so
if I write "m" it will take it as a >99 number (because of the integer value of "m") therefore displaying the "you can't be that old" message. but how can I fix this so the program displays "Please enter a number" when a letter is entered? (If anyone could fix the code and write it in a way that works, I'd
be forever grateful).
Any suggestions, tips or hints are very welcome.
so if I write "m" it will take it as a >99 number (because of the integer value of "m")
No, "m" can't be inputted into an int, cin will fail here. So what you should do is to check the status of cin, such as
if (cin >> age) {
// ok
if (age < 99)
{
...
} else
{
...
}
}
else
{
// failed
cout << "That is not a number, Please Enter a Valid Number\n";
system("pause");
system("cls");
cin.clear(); // unset failbit
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // skip bad input
goto backtoage;
}
Check the behavior of std::basic_istream::operator>>
If extraction fails (e.g. if a letter was entered where a digit is expected), value is left unmodified and failbit is set.
BTW: goto is almost obsolete in modern c++ programming. It should be easy to implement the same logic with a loop.
LIVE
You can Try it.It will validate numeric input in C++.Here cin.good() function is return true if the input is valid, if it is not valid it will return fase. cin.ignore() is used to ignore the rest of the
input buffer, which contains the erroneous input and cin.clear() is
used to clear the flag.
#include <iostream>
#include<string>
#include <limits>
using namespace std;
int main() {
backtoage:
int age = 0;
cout << "How old are you?\n";
cin >> age;
if(cin.good()){
if (age < 99){
cout << "Perfect!\n";
system("pause");
}
else if (age > 99){
cout << "You can't be that old, Try again.\n";
system("pause");
system("cls");
goto backtoage;
}
}
else{
cout << "That is not a number, Please Enter a Valid Number\n";
system("pause");
system("cls");
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
goto backtoage;
}
return 0;
}
Input/Output:
How old are you?
k
That is not a number, Please Enter a Valid Number
How old are you?
120
You can't be that old, Try again.
How old are you?
10
Perfect!
first of all , if the users can enter characters like 'm' 'k' or anything else , I suggest using string , then if you want to change to number just substract '0' , so you can work with numbers, secondly programmers , usually do not use goto statement because it can be dangerous and make underfiend behaivor appear into your program.
Sorry for my bad english.
#include<iostream>
#include <string>
using namespace std;
int main()
{
string input;
getline(cin, input);
unsigned int lenght = input.size(),age=0;
for (int i = 0; i < lenght; ++i) {
if (input[i] >= '0' && input[i] <= '9') {
age = age*10+(int)input[i]-'0';
}
}
if (age > 99)
cout << "Nice try , you can`t be that old\n";
else
cout << "perfect!\n";
return 0;
}

C++ input not being read

I just started with c++ (coming from java) and I'm trying to do some basic exercises. The idea is to ask for any input other than 5, if the user inputs 5, display a message, and if the user inputs anything other than 5 ten times, display another message. Here's the code:
void notFive () {
int count = 0;
while (count < 10) {
int input = 0;
cout << "Enter any number other than 5." << endl;
cin >> input;
if (input == 5)
break;
count++;
}
if (count == 10)
cout<<"You are more patient than I am, you win.";
else
cout << "You weren't supposed to enter 5!";
}
}
My problem is that all this code does is print out "Enter any number other than 5." 10 times, then say "You are more patient that I am, you win." any ideas what is wrong?
if you guys want all my code (to make sure I'm not just being an idiot) here it is:
#include <iostream>
#include <stdio.h>
using namespace std;
class Hello {
public:
void notFive () {
int count = 0;
while (count < 10) {
int input = 0;
cout << "Enter any number other than 5." << endl;
if ( ! (cin >> input) ) {
cout << "std::cin is in a bad state! Aborting!" << endl;
return;
}
if (input == 5)
break;
count++;
}
if (count == 10)
cout<<"You are more patient than I am, you win.";
else
cout << "You weren't supposed to enter 5!";
}
}hello;
int main() {
Hello h;
h.notFive();
return 0;
}
Your code works perfectly for me (in Visual Studio 2012) when I change notFive to main. Your problem must lie outside this code (possibly because cin is in a broken state, as others have suggested).
Change this line:
cin >> input
To this:
if ( ! (cin >> input) ) {
cout << "std::cin is in a bad state! Aborting!" << endl;
return;
}
The behavior you describe is what would happen if Something Bad happened to cin before this code was run.
Edit:
Add this same code to earlier uses of cin to find out where it's entering a bad state.
An example of this happening would be if the code tried to read an int, and the user typed a letter of the alphabet.
You can also call cin.clear(); to restore the working state of cin.
Here are my comments:
fflush(stdin) is not valid. The stdin cannot be flushed. Also,
this may not be the same input as cin.
You need to check for cin.fail after cin >> input. If I enter a
letter, your input statement will fail.

How to translate cout/cins to printf/scanfs?

I coded an easy game. I know how to use cout/cin but having problems with printf/scanf. The code below works well with cout/cin. Question is, how to convert them into printf/scanf? Why the codes in comment don't work?
Edit: I mean if I delete cout/cin lines and when I use printf/scanf instead it doesn't work properly.
#include <iostream>
#include <time.h>
using namespace std;
int main()
{
srand(time(NULL));
int min=0, max=1000, guess, counter=0;
bool winner=false;
char answer;
while(counter<10){
guess = rand()%(max-min)+min;
// printf("Did you pick %d? \t", guess);
// scanf("%c", &answer);
cout << "Did you pick " << guess << "?\t";
cin >> answer;
if(answer=='y'){ // yes
winner=true;
// printf("Computer wins.\n");
// printf("You picked: %d", guess);
cout << "Computer wins." << endl;
cout << "You picked: " << guess;
break;
}
else if(answer=='m'){ // more
min=guess;
counter++;
}
else if(answer=='l'){ // less
max=guess;
counter++;
}
}
if(winner==false){
// printf("User wins.\n");
cout << "User wins." << endl;
}
return 0;
}
The problem is that scanf() doesn't remove the newline '\n' character from stdin, so on the next iteration the next scanf() reads it and tries to process it, seeming to ignore the input.
Try this instead:
scanf("\n%c", &answer);
That way, you expect the newline and scanf() consumes it.