I'm building a product checkout piece of software and I keep hitting a strange bug. I have a central menu that gets user input. After a function is finished with its task, it sends the user back to the menu. For certain functions, however, the cin.get() I have after the menu prompt bugs out and won't accept the first command given. Here are the relevant code fragments:
The main menu loop:
bool foreverLoopFlag = true;
while (foreverLoopFlag) {
cout << "\nC[heckout], R[eturn], S[tudent], P[roduct], Q[uit]. Choice? ";
cin.get(actionChoice);
std::cin.ignore(std::numeric_limits<streamsize>::max(),'\n');
cout << endl;
actionChoice = toupper(actionChoice);
switch (actionChoice) {
case 'C':
checkoutSoftware(studentMap, productList);
break;
case 'R':
returnSoftware(studentMap, productList);
break;
case 'S':
studentDisplay(studentMap, productList);
break;
case 'P':
productDisplay(studentMap, productList);
break;
case 'Q':
foreverLoopFlag = false;
break;
default:
cout << "Invalid command.\n";
break;
}
}
A problem-child function, studentDisplay:
void studentDisplay(map<string, Student> & studentMap, list<Product> & productList) {
string inputCLID;
cout << "Please enter student CLID: ";
cin >> inputCLID;
if (studentMap.find(inputCLID) != studentMap.end()) {
cout << "\nStudent: " << studentMap[inputCLID].name << " (" << inputCLID << ")\n";
cout << "\tBorrowed items: " << endl;
for (list<Student::LentProduct>::iterator it = studentMap[inputCLID].checkedOut.begin();
it != studentMap[inputCLID].checkedOut.end(); it++) {
cout << "\t\tProduct: " << (*it).name;
cout << "\tDue Date: " << (*it).dateDue << endl;
}
} else {
cout << "\nError: CLID not in database.\n";
}
}
Some of the indention was mangled moving over to SE, I apologize. Here an example of the issue I'm having:
C[heckout], R[eturn], S[tudent], P[roduct], Q[uit]. Choice? s
Please enter student CLID: mrx8394
Student: Mark Xeno (mrx8394)
Borrowed items:
Product: Bluebeard Due Date: 12/14/2013
C[heckout], R[eturn], S[tudent], P[roduct], Q[uit]. Choice? c
Invalid command.
C[heckout], R[eturn], S[tudent], P[roduct], Q[uit]. Choice? q
I tried putting a std::cin.flush() at the beginning of the menu-loop, but that didn't work. I tried doing std::cin.ignore(std::INT_MAX) at the beginning of the menu-loop, but that makes it to where the menu never even shows up. I also tried a std::cin.sync(), but that just makes an infinite cycle of this:
C[heckout], R[eturn], S[tudent], P[roduct], Q[uit]. Choice?
Please enter a product to checkout:
Error: No such product.
I have no idea where to go from here. I know it is probably just some quirk of the iostream that I'm not picking up on. Any assistant would be appreciated.
EDIT: I do not have enough reputation to upvote or comment on specific answers (all of my rep is on Math.SE!!!), so I'll comment here. #Igor-tandetnik 's solution worked perfectly. I had moved everything else over to a getline, but I suppose that guy just got left in the shuffle. My thanks come in droves.
#qwrrty While it may be folly, I had a specification to meet (don't you just love low level University courses). I don't typically ask for help debugging assignments, but this was the last bug and my knowledge of iostream isn't that deep, but I knew someone on here would know what was bugging out my stream state.
Thanks again guys, cheers!
cin >> inputCLID reads characters up to, but not including, the first whitespace character (in your example, a line feed). That character is left in the stream. It is that character that cin.get(actionChoice) later retrieves.
I tend to think that for interactive input, trying to use stdin and/or cin for reading anything other than a full line of input is folly. There are just too many ways for your program to get confused about what's still on the input stream, and end up in an unrecoverable state.
At the very least I'd modify the program to say what command it thinks is invalid, or product that doesn't exist:
default:
cout << "Invalid command '" << actionChoice << "'\n";
and
cout << "Error: No such product '" << productChoice << "'\n";
That way at least you can get an idea of what input the program is actually using for these variables.
Related
So I've been learning how to use the "switch" statement recently. I decided to do some practice exercises. The code I show in my sample code below is one I came up with myself as a solution for a "Cola Machine" beginner exercise I found on a website "cplusplus". The exercise problem text can be found as a multi-line comment at the top of my code. Though, I did decide to try to make my code do more than what was required of the exercise.
For the most part, this code works exactly how I want it to. At first I even struggled to figure out how to get the code to repeat the user input in the line switch (cin.get()), if they had entered an invalid answer, but I solved this issue by nesting the "switch" statment inside of a "for" statement, for (int x = 0; x < 1; x++), and having the invalid answers decrement the counter ( x--; ). Not sure if that's a practical solution, but it's the one I came up with.
The only time my program doesn't run as intended is when a multiple character input that contains both valid answers and invalid answers is entered into the program (i.e. "-1" or "17"). The latter example outputs the statement for only the valid part of the answer, the statement for case '1', where as the former example outputs the statements for invalid answers and valid answers, so the default case and case '1'. Example for input "-1"
I'm wondering if that's just a problem that is inherent to using using "switch" statements in general, or if there's a practical solution I've yet to learn. I'm using a book to learn how to code, "C++ How To Program" by H.M. Deitel/P.J. Deitel, and they had given me a sample code for a letter grade counting program that can be found in my previous question on here. And I found that this same problem occurs in that sample code.
I'd be happy to hear any and all solutions, thank you ! :)
/* Write a program that presents the user w/ a choice of your 5 favorite beverages (Coke, Water, Sprite, ... , Whatever).
Then allow the user to choose a beverage by entering a number 1-5.
Output which beverage they chose.
>> Modify the program so that if the user enters a choice other than 1-5 then it will output "Error. choice was not valid, here is your money back." */
#include <iostream>
#include <string>
using std::cout;
using std::cin;
using std::endl;
using std::string;
int main()
{
string drink1 = "Water", drink2 = "Coke", drink3 = "Pepsi",
drink4 = "Orange Juice", drink5 = "Powerade";
string choose_text = "\n\nChoose your preferred drink: ", chosen_text = "\nYou have chosen: ";
cout << "1.) " << drink1.append(17 - drink1.length(), ' ') << "2.) " << drink2.append(17 - drink2.length(), ' ')
<< "3.) " << drink3.append(17 - drink3.length(), ' ') << "4.) " << drink4.append(17 - drink4.length(), ' ')
<< "5.) " << drink5.append(17 - drink5.length(), ' ') << choose_text;
for (int x = 0; x < 1; x++) {
switch (cin.get()) {
case '1':
cout << chosen_text << drink1 << endl;
break;
case '2':
cout << chosen_text << drink2 << endl;
break;
case '3':
cout << chosen_text << drink3 << endl;
break;
case '4':
cout << chosen_text << drink4 << endl;
break;
case '5':
cout << chosen_text << drink5 << endl;
break;
case '\n': case ' ':
x--;
break;
default:
cout << "\nError. Choice was not valid.\nPlease enter an option 1 - 5." << choose_text;
x--;
break;
}
}
return 0;
}
You can do this:
int answer;
cin >> answer;
That will retrieve an integer value from the user instead of a single character. That solves part of your problem.
Now, let's look at your loop. Ick. Let's try this:
bool keepWorking = true;
do {
keepWorking = false;
int answer;
cin >> answer;
switch (answer) {
...
set keepWorking to true on the bad answers
}
} while (!cin.eof() && keepWorking);
I have written a program with several menus within it. I am now debugging the program and I wanted to include some input validation in the menu choices. However, for some reason, when it detects a wrong input it goes back to the beginning of the function with a goto statement (I know, bad practice :\) and It asks the user for a new input, but even if the input is right, it goes back to the case for non allowed inputs (default) no matter what. Does anyone have any idea of what's going on?
NOTE:
select_variable_check(vector<int> , int) is a function that checks if the value entered has been entered before if that is of any relevance, although I don't think it has anything to do with it.
void select(vector<int>&select_control) {
char select;
choices:
cin >> select;
int selectint = select;
bool check = select_variable_check(select_control, selectint);
switch (select) {
case ('1','2','3','4','5','6','7','8','9','10'):
if (check == false) {
string city = city_selection(selectint);
double xcoor = xcoor_selection(selectint);
double ycoor = ycoor_selection(selectint);
cout << "\n" << city << "\n";
select_control.push_back(selectint);
cout << "\n Enter next city: ";
cin >> select;
selectint = select;
}
else {
cout << "You have already selected that city, please select another one ";
cin >> select;
}
break;
case '99': {
cout << "TERMINATING" << endl;
Sleep(3000);
exit(0);
break;
}
case '100': {
cout << "input complete" << endl;
break;
}
default: {
cout << "not a valid value, please try again" << endl;
goto choices;
break;
}
}
The value of ('1','2','3','4','5','6','7','8','9','10') is '10', so that's the only value that will trigger that first case statement. The right way to write this is:
case '1':
case '2':
case '3':
...
Even with this change, though, '10' is a peculiar kind of character, and almost certainly not the right thing here.
Your code boils down to
start:
get_input
process_input
if good do something
else go to start
end:
Now when you enter bad input it goes back to start. Your input operation will fail again as the input stream is still in an error state so you do not get new input and since you have bad input you go back to start. To stop this loop you need to clear out the error flags on the stream and remove any input still in the buffer. That will make you default case look like
default: {
cout << "not a valid value, please try again" << endl;
cin.clear(); // removes error flags
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // flushes input buffer
goto choices;
break;
}
You will need to #include <limits> to use cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n')
I am using Microsoft Visual studio 2013
I currently have this switch statement:
switch (option)
{
case 1:
getline(cin, newname);
cout << "What would you like your new username to be?\nName: ";
getline(cin, newname);
name = newname;
cout << "\nYour username is now '" << name << "' with your balance being $" << balance << "\n";
options();
break;
case 2:
cout << "\nOpenning cheat menu\n";
cheats();
break;
default:
cout << "\nExitting to main title...\n";
title();
break;
}
you can just ignore the case 2 and default, just showing so you know that those cases work. Case 2 and default work perfectly fine but case 1 is acting weird. As you can see on case 1 I have two getline(cin, newname); You may think I should only have one, but for some reason I need two for this code to function correctly.
If I only have one of these the code jumps past the input the user should give. If I have two it works normally.
I have asked someone this and they do not understand either, so therefore: Why does this work.
Apparently you have leftover input including a newline, in the input buffer of cin. That happens when you use other input operations than getline. They generally don't consume everything in the input buffer.
Instead of the extra getline you can use ignore, but better, do that at the place where you earlier do the inputting.
I think a similar problem has been posted here.
You need to flush the newline with cin.ignore() or cin.sync().
The first call also seems misplaced...
cin >> subchoice;
switch(subchoice)
{
case 1:
gold = gold - 5;
cout << "Now you only have " << gold << " gold.\n";
cout << "blah blah";
health = 100;
break;
case 2:
cout << "blah blah"
<< "1 - Head Back in and Buy a Bed\n"
<< "2 - Find a Clothier Shop\n"
<< "3 - Find a Blacksmith's\n";
cin >> subsubchoice;
switch(subsubchoice)
{
case 1:
gold = gold - 5;
cout << "Now you only have " << gold << " gold.\n";
cout << "blah blah"
health = 100;
break;
case 2:
menuchoice = subsubchoice;
break;
case 3:
menuchoice = subsubchoice;
break;
}
}
break;
case 2:
}
} while (!boolchoice);
Hey so I have this piece of code here. And whenever I run it, it always skips the cin input for subsubchoice. What it is supposed to do is take that input and either make you go into the inn or make apply that choice to menuchoice and restart you back at the beginning of the do-while loop. I have no idea why it is skipping the input and then closing out of the program. Any help is appreciated.
Maybe you need to add cin.ignore() before cin >> subsubchoice;
Could you explain the format of your input? cin reads all input until a whitespace character ('\n', '\t', ' ' etc.) is found. Is there any possibility you insert a whitespace in your original input, such as "2 1"?
Here you are:
There is a missing semi-colon in cout << "You quickly head back into the warm inn and relax into a warm night and sleep well. Your health is restored to 100.\n";
remove the last case 2: or add a break; after it (better remove it, it is useless).
while (!boolchoice) is guaranteed to be false, because in order to enter the forst if, boolchoice has to be non-zero. if you want it to iterate, try using while (gold) or while (health) to exit when you are either out of gold or health...
I hope this helps...
So I'm having some problems when using cin and switch statements.
First, the program prompts for an int:
cout << "How many registers would you like to use?: ";
cin >> kassor;
Later on, the user is asked to make a choice:
cout << endl << "Press \"S\" to run the queue simulator and/or make a timestep." << endl;
cout << "Press \"Q\" to quit." << endl << endl;
cout << "Choice: ";
cin >> choice;
switch (choice)
{
case 's':
case 'S':
{
cout << "test";
nya = newCustomers();
break;
}
case 'q':
case 'Q':
{
return 0;
}
}
Here, the 'q' option works fine, but the 's' option does not. It 'hangs', as if still waiting for input. I have tried various cin.ignore() and such, but to no avail.
What puzzles me is that
switch (choice)
{
case 's':
case 'S':
{
cout << "test";
nya = newCustomers();
break;
Gives nothing, but the following:
switch (choice)
{
case 's':
case 'S':
{
cout << "test";
cin.ignore(1024, '\n');
nya = newCustomers();
break;
outputs 'test'.
My main question here is: Is the problem cin or something in the case: s ?
Thank's in advance :
It looks like the function newCustomers is getting hung up on a stray character or two after the input to choice. That would explain why the ignore call "fixes" the problem, and it's the solution suggested in the comment by #TheBuzzSaw.
To see this more clearly, change
cout << "test";
to
cout << "test\n";
or to
cout << "test" << std::endl;
On some systems the console is line-buffered, so you won't see any output until the program writes a newline. Inserting endl flushes the output buffer, so you should see the message even if subsequent code hangs. Or change it to:
cerr << "test\n";
cerr is more aggressive about flushing buffers, precisely because it's used for error output that you don't want to miss.
Short Answer:
I believe cin is failing somewhere or it is the cause of unexpected behavior
I cannot pinpoint it without more code.
Edit: I cannot post a comment on your post, so I figured I would post here. The "hanging" could be an infinite loop. If you are doing something like what I am doing and looping to get input and fail to clear the error bits cin will constantly fail. If you are not cout'ing something each time you ask for input it could just be quietly sitting there looping through that input-gathering function. Put breakpoints in all of your loops and step through with the debugger to verify none of your loops are infinite looping.
Try adding a std::cin.clear(); before the .ignore() in your second test case. See if that stops your hanging.
Explanation:
cin can fail. This can cause weird behavior. A common way for it to fail is if you are reading into an integer and you get character input. Once cin fails it sets a fail bit and from then on, cin does not behave like you would expect.
I would recommend not using a bare cin >> choice, because it can fail and you wont know it. I would abstract this out to a method that gets the proper input you want.
I personally keep a tiny utility library(.h) and .cpp around to include in projects where I am using common functionality I have already coded.
I have a readIntBetween() function which accepts 2 integers and reads from standard input an integer between those two numbers. If the user does not provide the right input (integer over or under bounds, or input containing a character) I ask them to re-enter the input.
In this function I make sure to clear the fail bits when I have detected a failure, and I ignore something like 200 characters to "flush" it out.
Here is the code to my readIntBetween function. I hope it helps you diagnose your error and fix it:
int readIntBetween(int lower, int upper, std::string prompt)
{
bool goodVal = false;
int value = -1;
do
{
std::cout << prompt ;
std::cin >> value;
if ( value >= lower && value <= upper)//check to make sure the value is in between upper and lower
goodVal = true;
else
{
if(std::cin.fail())
{
std::cout << "\tError - invalid format for integer number" << std::endl;
//clear all status bit including fail bit
std::cin.clear();
//flush input buffer to discard invalid input
std::cin.ignore(1000, '\n');
}
else
std::cout << "Value is not valid, must be between " << lower<<" and "<<upper<<"."<<std::endl;
}
}while(!goodVal);
return value;
}
If your cin is being used inside a loop, I recommend a different approach.
char buffer[64];
cin.getline(buffer, 64);
char choice = buffer[0];
switch (choice)
{
...
}
It is possible your cin is not being reset, and any extraneous characters are being fed into the subsequent requests for input. Grab more input and only process its first character.