Been working on a simple school project but I've run into a small problem in regards to validation of user input via the use of a while loop. The following code is used to do so:
cout << "How much woud you like to bet?[100, 300, 500]" << endl;
cin >> int_input;
if (cin.fail()){
int_input = 0;
}
//Validate check
while(int_input!=100 && int_input!=300 && int_input!=500){
cout << "Please enter a valid bet [100, 300, 500]" << endl;
cin >> int_input;
if (cin.fail()){
int_input = 0;
}
}
The issue arises when a non-integer is entered and the loop ends up spitting out the cout msg over and over again, skipping the request for new input. I assume that a non-integer always returns true for the while loop, but the program should still ask for user input, right?
The cin.fail is a recent addition and might not be necessary as it doesn't solve the problem, although I leave the code as it as it is.
If you have an error on the stream, you set your value to 0. So the loop is run again... and the error's still on the stream. Repeat.
You need to clear the error flag.
cin.clear();
Then extract enough "bad" data to get to the good part, or you'll just be right back where you started.
Related
Here's one of the return 0; sections I have in my main() function:
cout << "Would you like to remove a Pokemon? (Y/N): ";
cin >> removePokemonChoice;
cin.ignore(5, '\n');
if (toupper(removePokemonChoice) == 'Y')
{
deletePokemon();
cout << "New list:" << endl;
displayPokemon();
}
if (removePokemonChoice == -1)
return 0;
currently, it won't exit out of the program if the user enters -1. I can't use an else statement because I want the program to loop (there's a similar question after this bit that I want to come after) until -1 is entered.
Your program asks "(Y/N)" so I suppose removePokemonChoice is a char type... it is strange to expect -1 value from char data. By the way "-1" need 2 characters, so it must be string :-)
Think of it this way:
You're writing a program that asks you whether or not you want to remove a Pokemon. Normally, like in the actual game itself when Prof. Oak prompts you with a confirmation of do you want Charmander (and the answer is yes, you always go with the fire type, no exceptions). The choices the game will always give you is "Yes" or "No".
Would you ask a yes/no question and expect a numerical answer back? While it is true the compiler converts and does numerical stuff in the background, what you really should be thinking about is, is it intuitive to the user?
I am trying to get the user to input some data and then storing it in a structure, however I am having troubles knowing which function I should use and what's the difference? cin or getline()? Either function I use, it seems like it takes in the '\n' key and makes my program crash, but I am not 100% if that's the problem... Since it keeps crashing.
I've played around with both of them and here is what I have.
string temp;
int id;
cout << endl << "Full name (last, first): ";
cin >> temp;
cin.ignore(1, '\n');
myData[fileSize] = parseName(temp);
cout << endl << "ID: ";
cin >> id;
myData[fileSize].id = id;
cout << endl << "Address: ";
cin >> temp;
temp.copy(myData[fileSize].address, temp.length(), 0);
The variable fileSize is just which element the array is currently at and the function parseName splits the name into last and first.
I been reading on a couple of functions like, cin.ignore() and noskipws, but not sure how to use them. By the way, the way the user should input the data is "last, first", with a comma and white space after (this is what the parsing function is looking for).
Also I am not sure if the address section is the best way to do this, I have the structure myData.address to be a character array, because I don't know how to work with strings. I am still not confident with C++. Thanks for any help.
EDIT: If I comment out the ID and Address parts, the program loops itself 6 times saying I have an invalid entry (which is part of main), so it reads 6 or 7 keys after I press enter.
If I leave everything the way it is, this is what I get.
Full name (last, first): terminate called after throwing an instance of 'std::ou
t_of_range'
what(): basic_string::copy
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
Process returned 3 (0x3) execution time : 4.328 s
Press any key to continue.
You should use cin.getline() instead for this case, and the cin.ignore is not necessary.
Here is an examination of the two methods - std::cin.getline( ) vs. std::cin
Also, check your parseName function and try testing it in isolation without any user I/O.
simply trying to compare two user defined vectors to see if they are equal, current code:
vector<int> ivec1, ivec2; //vectors, uninitialized
int temp1;
cout << "Enter integers to be stored in ivec1." << endl;
while(cin >> temp1) //takes input from user and creates new element in the vector to store it
{
ivec1.push_back(temp1);
}
int temp2;
cout << "Enter integers to be stored in ivec2." << endl;
while(cin >> temp2) //same as above with different vector
{
ivec2.push_back(temp2);
}
if(ivec1 == ivec2)
cout << "ivec1 and ivec2 are equal!" << endl;
else
cout << "ivec1 and ivec2 are NOT equal!" << endl;
So far it lets me assign values to ivec1 just fine, but as I exit the while loop by entering a letter to make cin fail, it skips the second while block. Out of curiosity I tried putting in other cin statements after the first while loop, and it ignores them all as well.
Does forcing cin to fail cause the program to ignore all other calls for it or something, or is there another problem? If so, how can I get this program to do what I want?
screenshot for your viewing pleasure:
http://img695.imageshack.us/img695/2677/cinfailure.png
*PS. having temp1 and temp2 was just me trying to figure out if using the same int for both assignment loops was causing the problem, anyway I just figured I'd leave it there
You would have to do cin.clear() to reset the stream state. Then you will have to make sure that the offending character is read from the stream (using one of the techniques described here), so that the next input operation does not fail as well.
You mean that you a doing a ctrl-D to give end-of-file for the first loop.
The problem with that is that once EOF is achived it will persist and the second loop will also see the EOF and never read anything.
Instead use a terminating charater such as a blank line or a '.' and specifically test for that in toy while loop instead of while (cin >> tmp1)
Use cin.clear() between the loops. This command resets the state of the stream back to a usable one.
Might be helpful to know that you don't always have to enter an invalid character to exit a loop, you can also use (on windows) a ctrl-z (ctrl-d on other systems) on the console, which stimulates an EOF. You'd still have to cin.clear() (because an EOF still invalidates the stream) - but it's not as dangerous
When the first while loop exits because of failure of std::cin, it also sets the failure flag internally. All you need to clear that flag by writing the following after the first while loop:
scin.clear();
It clears all the failure flag, so that cin can be used to read further inputs.
I found this when I was working through the same problem. I had to add cin.clear() and cin.ignore() to reset the stream between loops and have it recognize the 'cin' calls again.
I am new to C++ and am in a class. I am trying to finish the first project and so far I have everything working correctly, however, I need the user to input a number to select their level, and would like to validate that it is a number, and that the number isn't too large.
while(levelChoose > 10 || isalpha(levelChoose))
{
cout << "That is not a valid level" << endl;
cout << "Choose another level:";
cin >> levelChoose;
}
That is the loop I made, and it sometimes works. If I type in 11 it prints the error, and lets me choose another level. However if the number is large, or is any alpha character it floods the screen with the couts, and the loop won't end, and I have to force exit. Why does it sometimes stop at the cin and wait for user input, and sometimes not? Thanks for the help!
This is an annoying problem with cin (and istreams in general). cin is type safe so if you give it the wrong type it will fail. As you said a really large number or non-number input it gets stuck in an infinite loop. This is because those are incompatible with whatever type levelChoose may be. cin fails but the buffer is still filled with what you typed so cin keeps trying to read it. You end up in an infinite loop.
To fix this, you need to clear the fail bit and ignore all the characters in the buffer. The code below should do this (although I haven't tested it):
while(levelChoose > 10 || isalpha(levelChoose))
{
cout << "That is not a valid level" << endl;
cout << "Choose another level:";
if(!(cin >> levelChoose))
{
cin.clear();
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
}
Edit: numeric_limits<> is located in the limits include:
#include<limits>
From your description, it seems likely (nearly certain) that levelChose is some sort of numeric type, probably an integer.
When you use operator>> to read a number, anything that couldn't be part of a number (e.g., most letters) will be left in the input buffer. What's happening is that you're trying to read the number, it's failing and leaving the non-digit in the buffer, printing out an error message, then trying to read exactly the same non-digit from the buffer again.
Generally, when an input like this fails, you want to do something like ignoring everything in the input buffer up to the next new-line.
levelChoose appears to be an integer type of some form (int, long, whatever).
It's not valid to input a character into an integer directly like that. The input fails, but leaves the character in the incoming buffer, so it's still there when the loop comes around again.
Here's a related question: Good input validation loop using cin - C++
I suspect the part while(levelChoose > 10..... This does not restrict level to less than 10 (assuming greater than 10 is a large number in your context). Instead it probably should be while(levelChoose < 10...
To check that an expression is not too large, the following could be a possibility to validate (brain compiled code!!)
const unsigned int MAX = 1000;
unsigned int x;
cin >> x;
while(x < MAX){}
I'm a programming student in my second OOP class, my first class was taught in C# and this class is taught in C++. To get our feet wet in C++, our professor has asked us to write a rather large program with File I/O. The problem is, I have a small part of my program that is not working, at least, not for me. The project requires that we code a loop to test if the file could be opened successfully, and the loop I have written doesn't seem to be working.
I don't get any compiler errors, but when I enter in the path to the file, either relative or absolute, it says it's invalid. I have a feeling it has something to do with my conditions in my do-while loop, but I can't pinpoint it.
I don't mean to bring my homework to SO, but I've been scratching my head for two+ hours, and I can't seem to figure this out.
Would you mind helping me fix my loop? And maybe explain what it is that I'm doing wrong? I want to learn.
Thanks!
Code:
Rainfall rData;
ifstream actualReader;
ifstream averageReader;
string aRDataLoc;
char response = 'a';
const int KILL_VALUE = 1;
double actualRainfallD;
double actualRainfallPassedArray[ARRAY_CAPACITY];
double averageRainfallPassedArray[ARRAY_CAPACITY];
int i = 0;
do
{
actualReader.clear();
cout << "\nPlease enter in the path to the file containing the actual rainfall data." << endl;
cout << "Path to file: ";
cin >> aRDataLoc;
actualReader.open(aRDataLoc.c_str());
if (!actualReader.is_open())
{
cout << "Invalid file path! Would you like to enter in a new file path?(y/n): ";
cin >> response;
if (response == 'n') { exit(KILL_VALUE); }
}
}while (!actualReader.is_open() && response == 'y');
I don't know what input you are giving to cin, but be aware that cin will stop at the first whitespace character it encounters. For example, if you give as input the following:
C:\Program Files\directory
then aRDataLog would have the value C:\Program .
In order to read the whole line, you could use getline.
Check also this post.
While I'm not exactly sure what the issue is here, it might be a good idea to print what you're getting from std::cin to ensure you're getting what you're expecting.
you need to put actualReader.close call in else, as the file has open handles and it is not available for open again