I am using an if statement to get the users input with a bool value, if they enter 1 then the program continues to execute, if they enter 0 then I want the program to stop running completely. This is the code im using.
bool subscription;
cout << "Would you like to purchase a subscription to our newspaper?\n";
cout << "Enter 1 if yes, and 0 if no. ";
cin >> subscription;
if(subscription == false)
{
cout << "We're sorry you don't want our services.";
//this is where i want the program to stop, after it outputs that line.
}
else if(subscription == true)
{
cout << "\nPlease enter your first and last name. ";
}
I have tried using return 0; after the cout statement, but that didn't work, it would just output the statement and then continue on with the program.
I also tried exit(); and that did the exact same thing.
The problem is that instead of the comparison operator you are using the assignment operator
if(subscription = false)
{
cout << "We're sorry you don't want our services.";
//this is where i want the program to stop, after it outputs that line.
}
else if(subscription = true)
{
cout << "\nPlease enter your first and last name. ";
}
In thsi expression of the if statement
if(subscription = false)
you assigned false to subscription and the expression is also equal to false. As the result the compound statement of this if statement is not executed.
Change the code as
if(subscription == false)
{
cout << "We're sorry you don't want our services.";
//this is where i want the program to stop, after it outputs that line.
}
else if(subscription == true)
{
cout << "\nPlease enter your first and last name. ";
}
It would be even better if you would write
if( subscription )
{
cout << "\nPlease enter your first and last name. ";
}
else
{
cout << "We're sorry you don't want our services.";
// here you can place the return statement
}
#include <iostream>
using namespace std;
int main()
{
bool subscription;
cout << "Would you like to purchase a subscription to our newspaper?"<<endl;
cout << "Enter 1 if yes, and 0 if no. "<<endl;
cin >> subscription;
if(!subscription){
cout << "We're sorry you don't want our services."<<endl;
//this is where i want the program to stop, after it outputs that line.
return -1;
}
else{
cout << "\nPlease enter your first and last name. "<<endl;
return 0;
}
}
A couple of guidelines:
Do not use var = true or var = false (use double == for comparison)
Do not user boolean variables var == true in comparisons with true or false, just use them directly as boolean conditions
Put "<<"endl" when using streams for line breaks better than \n
Use return in main function will return in that place, thus finishing your program.
Related
Please note that I am a complete beginner at C++. I'm trying to write a simple program for an ATM and I have to account for all errors. User may use only integers for input so I need to check if input value is indeed an integer, and my program (this one is shortened) works for the most part.
The problem arises when I try to input a string value instead of an integer while choosing an operation. It works with invalid value integers, but with strings it creates an infinite loop until it eventually stops (unless I add system("cls"), then it doesn't even stop), when it should output the same result as it does for invalid integers:
Invalid choice of operation.
Please select an operation:
1 - Balance inquiry
7 - Return card
Enter your choice and press return:
Here is my code:
#include <iostream>
#include <string>
using namespace std;
bool isNumber(string s) //function to determine if input value is int
{
for (int i = 0; i < s.length(); i++)
if (isdigit(s[i]) == false)
return false;
return true;
}
int ReturnCard() //function to determine whether to continue running or end program
{
string rtrn;
cout << "\nDo you wish to continue? \n1 - Yes \n2 - No, return card" << endl;
cin >> rtrn;
if (rtrn == "1" and isNumber(rtrn)) { return false; }
else if (rtrn == "2" and isNumber(rtrn)) { return true; }
else {cout << "Invalid choice." << endl; ReturnCard(); };
return 0;
}
int menu() //function for operation choice and execution
{
int choice;
do
{
cout << "\nPlease select an operation:\n" << endl
<< " 1 - Balance inquiry\n"
<< " 7 - Return card\n"
<< "\nEnter your choice and press return: ";
int balance = 512;
cin >> choice;
if (choice == 1 and isNumber(to_string(choice))) { cout << "Your balance is $" << balance; "\n\n"; }
else if (choice == 7 and isNumber(to_string(choice))) { cout << "Please wait...\nHave a good day." << endl; return 0; }
else { cout << "Invalid choice of operation."; menu(); }
} while (ReturnCard()==false);
cout << "Please wait...\nHave a good day." << endl;
return 0;
}
int main()
{
string choice;
cout << "Insert debit card to get started." << endl;
menu();
return 0;
}
I've tried every possible solution I know, but nothing seems to work.
***There is a different bug, which is that when I get to the "Do you wish to continue?" part and input any invalid value and follow it up with 2 (which is supposed to end the program) after it asks again, it outputs the result for 1 (continue running - menu etc.). I have already emailed my teacher about this and this is not my main question, but I would appreciate any help.
Thank you!
There are a few things mixed up in your code. Always try to compile your code with maximum warnings turned on, e.g., for GCC add at least the -Wall flag.
Then your compiler would warn you of some of the mistakes you made.
First, it seems like you are confusing string choice and int choice. Two different variables in different scopes. The string one is unused and completely redundant. You can delete it and nothing will change.
In menu, you say cin >> choice;, where choice is of type int. The stream operator >> works like this: It will try to read as many characters as it can, such that the characters match the requested type. So this will only read ints.
Then you convert your valid int into a string and call isNumber() - which will alway return true.
So if you wish to read any line of text and handle it, you can use getline():
string inp;
std::getline(std::cin, inp);
if (!isNumber(inp)) {
std::cout << "ERROR\n";
return 1;
}
int choice = std::stoi(inp); // May throw an exception if invalid range
See stoi
Your isNumber() implementation could look like this:
#include <algorithm>
bool is_number(const string &inp) {
return std::all_of(inp.cbegin(), inp.cend(),
[](unsigned char c){ return std::isdigit(c); });
}
If you are into that functional style, like I am ;)
EDIT:
Btw., another bug which the compiler warns about: cout << "Your balance is $" << balance; "\n\n"; - the newlines are separated by ;, so it's a new statement and this does nothing. You probably wanted the << operator instead.
Recursive call bug:
In { cout << "Invalid choice of operation."; menu(); } and same for ReturnCard(), the function calls itself (recursion).
This is not at all what you want! This will start the function over, but once that call has ended, you continue where that call happened.
What you want in menu() is to start the loop over. You can do that with the continue keyword.
You want the same for ReturnCard(). But you need a loop there.
And now, that I read that code, you don't even need to convert the input to an integer. All you do is compare it. So you can simply do:
string inp;
std::getline(std::cin, inp);
if (inp == "1" || inp == "2") {
// good
} else {
// Invalid
}
Unless that is part of your task.
It is always good to save console input in a string variable instead of another
type, e.g. int or double. This avoids trouble with input errors, e.g. if
characters instead of numbers are given by the program user. Afterwards the
string variable could by analyzed for further actions.
Therefore I changed the type of choice from int to string and adopted the
downstream code to it.
Please try the following program and consider my adaptations which are
written as comments starting with tag //CKE:. Thanks.
#include <iostream>
#include <string>
using namespace std;
bool isNumber(const string& s) //function to determine if input value is int
{
for (size_t i = 0; i < s.length(); i++) //CKE: keep same variable type, e.g. unsigned
if (isdigit(s[i]) == false)
return false;
return true;
}
bool ReturnCard() //function to determine whether to continue running or end program
{
string rtrn;
cout << "\nDo you wish to continue? \n1 - Yes \n2 - No, return card" << endl;
cin >> rtrn;
if (rtrn == "1" and isNumber(rtrn)) { return false; }
if (rtrn == "2" and isNumber(rtrn)) { return true; } //CKE: remove redundant else
cout << "Invalid choice." << endl; ReturnCard(); //CKE: remove redundant else + semicolon
return false;
}
int menu() //function for operation choice and execution
{
string choice; //CKE: change variable type here from int to string
do
{
cout << "\nPlease select an operation:\n" << endl
<< " 1 - Balance inquiry\n"
<< " 7 - Return card\n"
<< "\nEnter your choice and press return: ";
int balance = 512;
cin >> choice;
if (choice == "1" and isNumber(choice)) { cout << "Your balance is $" << balance << "\n\n"; } //CKE: semicolon replaced by output stream operator
else if (choice == "7" and isNumber(choice)) { cout << "Please wait...\nHave a good day." << endl; return 0; }
else { cout << "Invalid choice of operation."; } //CKE: remove recursion here as it isn't required
} while (!ReturnCard()); //CKE: negate result of ReturnCard function
cout << "Please wait...\nHave a good day." << endl;
return 0;
}
int main()
{
string choice;
cout << "Insert debit card to get started." << endl;
menu();
return 0;
}
I am currently working on a text based adventure game as a project for class. I have mostly everything started and working fine. The only problem is when I ask the user which room they want to change to, if they enter a blank input, then a message should output saying "You must choose a room." For the life of me I cannot figure it out. Any help is much appreciated.
Code:
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int main() {
bool game_play = true;
bool game_start = true;
int room_change;
int room_current = 0;
while (game_play == true) {
if (game_start == true) {
srand((unsigned int)time(NULL));
room_change = rand() % 2 + 1;
game_start = false;
}
else {
for (bool check = false; check == false;) { // Check if input is invalid
cin >> room_change;
if (cin.fail()) {
cout << "Choose an existing room.";
cin.clear();
cin.ignore();
}
else if (room_change == room_current) {
cout << "You're already in that room.";
}
else {
check = true;
}
}
}
switch (room_change) {
case 1:
cout << "You are in room 1.";
room_current = 1;
break;
case 2:
cout << "You are in room 2.";
room_current = 2;
break;
case 3:
game_play = false;
break;
default:
cout << "That room doesn't exist.";
}
}
return 0;
}
I just ran your code and when you hit enter, it will keep waiting until you enter a number or something invalid such as a character or a string. I did find that if you change your code from
cin >> room_change;
to
cin >> noskipws >> room_change;
when the user inputs a blank, it will cause the cin.fail() to return true and then proceed to print "Choose an existing room."
In your situation, the while loop will keep getting called until we have valid input. The "Choose an existing room" does get repeated because room_change is an integer, so when we hit enter, the '\n' will be left in the buffer. The while loop on the next iteration then reads that '\n' and executes the cin.fail() before letting you input something else. One solution I found is to use more cin.ignore() statements.
for (bool check = false; check == false;) { // Check if input is invalid
cin >> noskipws >> room_change;
if (cin.fail()) {
cout << "Choose an existing room.";
cin.clear();
cin.ignore();
} else if (room_change == room_current) {
cout << "You're already in that room.";
cin.ignore();
} else {
check = true;
cin.ignore();
}
}
The reason is because we want to get rid of that '\n' so that the cin.fail() does not execute. However, I did find that when you input a character, it will print "Choose an existing room" twice. It will print the first time because a character is not an integer, and a second time because of that '\n'.
The only problem is when I ask the user which room they want to change to, if they enter a blank input, then a message should output saying "You must choose a room."
Using std::getline and then extracting the number from the line using a std::istringstream is a better strategy for that.
std::string line;
std::cout << "Choose an existing room. ";
while ( std::getline(std::cin, line) )
{
// Try to get the room_change using istringstream.
std::istringstream str(line);
if ( str >> room_change )
{
// Successfully read the room.
break;
}
// Problem reading room_change.
// Try again.
std::cout << "Choose an existing room. ";
}
#include <iostream>
using namespace std;
int main(){
int room_change=200;
cout<<"Enter Blank";
cin>>room_change;
if(room_change==NULL){
cout<<"There is NO-THING"<<endl;
}
if(room_change!=NULL){
cout<<"There is something and that is :"<<room_change<<endl;
}
return 0;
}
But a much simpler approach to this would be to use Strings. If this is a Homework of sort and you are limited to Integer variable only. Its much more complicated if you want to detect if an Buffer is empty or not. Regardless of homework limitation, the OS layer input is String based. How can I use cin.get() to detect an empty user input?
I'm a beginner in programming, and I'm trying to make a program that calculated how much radiation you've been exposed to throughout your life. For some reason, the 'cin' in my xray function doesn't accept user input, and just exits with code 0.
#include <iostream>
#include <conio.h>
#include <windows.h>
#include <stdlib.h>
#include <string>
#include <sstream>
using namespace std;
bool nearpowerplant;
int XRay; // the amount of times you got an x-ray
double tRads = 0; // your total dose of radiation in your lifetime, measured in mSv (millisievert)
int age;
//the sleep function
void sleep() {
Sleep(1000); // 1000 miliseconds = 1 second
}
/*
>system("CLS")< for clear the console
*/
//introduction and pretty much the menu
void intro() {
cout << "Welcome to the Radiation Level Calculator" << endl;
sleep();
cout << "Conceptualized and created by Anatoly Zavyalov" << endl;
sleep();
cout << "Press the ENTER key to begin." << endl;
cin.get();
}
//introduction to general questions
void genintro() {
// intro to the medical
system("CLS");
sleep();
cout << "Let's begin with general questions." << endl;
sleep();
cout << "Press the ENTER key to continue." << endl;
cin.get();
}
//medical questions
void Age() {
//age
system("CLS");
cout << "How old are you?\n" << endl;
sleep();
cin >> age;
if (age <= 0) {
cout << "Your age can't be less or equal to 0." << endl;
Age();
}
else {
tRads += (age * 2);
sleep();
cout << tRads << endl;
}
}
//live close to powerplant?
void powerplant() {
system("CLS");
cout << "Do you live within 75 kilometers of a nuclear powerplant?" << endl;
sleep();
cout << "If yes, type YES. If no, type NO." << endl;
cin >> nearpowerplant;
if (nearpowerplant = "YES") {
tRads += (age * 0.01);
}
else {}
sleep();
cout << tRads << endl;
}
void xray() {
system("CLS");
cout << "How many times have you had an x-ray?\n" << endl;
sleep();
cin >> XRay;
if (XRay < 0) {
cout << "You can't have an x-ray a negative amount of times." << endl;
}
else {
tRads += (XRay * 3.1);
}
sleep();
cout << tRads << endl;
}
//main function, put all of the loops into here
int main() {
intro(); // the introduction
genintro(); // medical intro
Age(); // asks for age
powerplant(); // asks if lives close to powerplant
xray(); // asks for x-ray
return 0;
}
EDIT: I have edited the post to include the whole code. By the way, I am using Visual Studio Community 2017.
bool nearpowerplant;
nearpowerplant is a bool. It is true or false. That is it. It's worth noting that there is no reason for this variable to be globally accessible and consuming storage for the entire run of the program. It is used twice in the program, both times in the same function. It should be an Automatic variable scoped by the function that uses it.
cout << "If yes, type YES. If no, type NO." << endl;
cin >> nearpowerplant;
Reading "YES" or "NO" into a variable of type bool fails. cin cannot convert the string input into a boolean value and cin stops accepting input until the error is cleared. It's also a good idea to remove the garbage input that caused cin to fail or guess what? cin's just going to fail again. There are hundreds of SO questions on how to handle this, so I'm just going to drop keywords here: clear and ignore.
Takeaways: Make sure the data entry matches the type of the data being entered into and test the stream after every read to make sure the read succeeded.
eg:
if (cin >> nearpowerplant)
{
// do stuff
}
else
{
// clean up
}
This solves OP's visible error, but since it is heavily entwined with the next bug they are likely to find, we might as well cover it as well.
if (nearpowerplant = "YES") {
tRads += (age * 0.01);
}
else {}
if (nearpowerplant = "YES") { uses = (assignment) where it should use == (comparison). C++ is unforgiving here because this will compile. What it really did was takes the address of the string literal "YES", test that it's not null, and set nearpowerplant to the result. Since the address of the string literal is never going to be NULL, the result is always true, and when the if tests the result, the if will always enter.
Eg: http://ideone.com/4QL2jn
So what we need is something more like
cout << "If yes, type YES. If no, type NO." << endl;
string temp;
cin >> temp;
if (temp == "YES") {
tRads += (age * 0.01);
}
else {}
Note this will skip if the user inputs "yes", "y", "Yes" or anything other than exactly "YES". How you deal with this is up to you, but std::tolower and std::transform may help somewhat.
I think with sleep() comes undefined behavior, you should test it without, the os handles user-input and you do not have to care about the user typing in. endl flushes cout, so the text is directly shown.
Edit:
Maybe system("CLS") or sleep produces a silent error.
I tried to make a an introduction to a "game", and in its functions I made some Yes/No, 1/2/3, situations.
Im new to this however it wasn't that difficult, worked perfectly. The problem appeared when handling with invalid inputs. So this is what the code looks like by now:
#include "Introduction.h"
#include "GameConstants.h"
#include "PlayerCharacter.h"
#include <iostream>
#include <windows.h>
using namespace std;
Introduction::Introduction()
{
}
/////////Function N.1///////////
void Introduction::presentation()
{
char confirm;
string enteredName;
cout << constants.line() << "Welcome traveler! What is the name?" << endl;
getline(cin,enteredName);// Gets the WHOLE LINE as the name.
while (confirm != 'Y') //If the player doesn't confirm the name with 'Y' in will run again until it does.
{
cout << constants.xline() << "Your name is " << enteredName << " right? (Y/N)" << endl;
cin >> confirm; //The player's answer
cin.sync(); //Only takes the first character
confirm = toupper(confirm); //Turns player message into CAPS for easier detection in the "if" statements
if (confirm == 'N'){ //If not the correct name, gives another chance
cout << constants.xline() << "Please, tell me your name again..." << endl;
cin >> enteredName;
cin.sync();}
if ((confirm != 'Y')&&(confirm != 'N')){ //If an invalid input is entered, gives another chance. And insults you.
cout << constants.xline() << "Fool Go ahead, just enter your name again." << endl;
cin >> enteredName;
cin.sync();}
}
if (confirm == 'Y'){ //When the answer is yes ('Y') /* Uneeded line */
PC.setName(enteredName); //Saves the name
cout << constants.xline() << "Excellent! I have a few more questions for you " << PC.name() << "..." << endl;
}
}
//////////Function N.2///////////
void Introduction::difSelection(){
int selectedDif = 0; //Variable to store selected difficulty whitin this function.
Sleep(2500);
cout << constants.xline() << "What kind of adventure do you want to take part in?" << endl;
Sleep(2500); //Wait 2,5 s
cout << "\n1= Easy\n2= Normal\n3= Hard" << endl;
while(selectedDif != 1&&2&&3){ //Selected option must be 1/2/3 or will run again
cin >> selectedDif; //Sets the user selected difficulty
cin.sync(); //Gets only first character
if((selectedDif != 1||2||3)&&(!(selectedDif))){ //If the input isn't 1/2/3 AND is an invalid character, this will run. And it'll start again
cout << constants.xline() << "Criminal scum. Go again." << endl;
cin.clear();
cin.ignore();
}
if(selectedDif != 1&&2&&3){ //If selected option isn't 1/2/3, this will run and will loop again. However I know this conflicts with the previous statement since this will run anyways.
cout << constants.xline() << "Wrong input, please try again." << endl;
}
else if(selectedDif == 1){
constants.setDiff(1);
constants.setStatPoints(15);
} else if(selectedDif == 2){
constants.setDiff(2);
constants.setStatPoints(10);
} else if (selectedDif == 3){
constants.setDiff(3);
constants.setStatPoints(5);}
}
}
The first function works perfectly you can type "aaa" or "a a a" and will work. However I'd like to know if there's a simpler way to do it. (Understandable for a beginner, just started 3 days ago lol; if it includes some advanced or less known code prefer to stay like this by now).
Now, the second one, I really have no idea how to fix it. I need something that if the user's input was an invalid character type, throw certain message, and if it's an int type, but out of the range, another message. And of course, run again if it fails. Did a lot of search and couldn't find anything that meet this requirements.
To check if the user input is an int, you could use the good() function.
int val;
cin >> val;
if( cin.good() ) {
// user input was a valid int
} else {
// otherwise
}
As for the range check, the syntax is a bit different.
This returns true if the number is not equal to 1 nor 2 nor 3:
selectedDif != 1 && selectedDif != 2 && selectedDif != 3
Another shorter way would be to use:
selectedDif < 1 || selectedDif > 3
Another thing, in c++, there are two keywords break and continue which will allow to reduce the code in the loops.
I just started learning C++ after previously coding with Java. The code below takes input from the user and validates the input. The first piece asks for the number of voters, which must be a positive number. If I enter a negative number the program behaves as I expected. It prints out the error message and asks for the input again. However, if I enter any other character, such as any alphabet letter I get an infinite loop in the console, asking for input and printing the error message. What am I doing wrong?
my code:
#include <iostream>
using namespace std;
struct dataT {
int numOfVoters = -1;
float preSpread = -1;
float votingError = -1;
};
void getUserInfo() {
dataT data;
while (data.numOfVoters == -1) {
cout << "enter the number of voters" << endl;
cin >> data.numOfVoters;
if (data.numOfVoters <= 0) {
data.numOfVoters = -1;
cout << "Invalid entry, please enter a number larger than zero." << endl;
}
}
while (data.votingError == -1) {
cout << "enter the percentage spread between candidates" << endl;
cin >> data.votingError;
if (data.votingError <= 0 || data.votingError >= 1) {
data.votingError = -1;
cout << "Invalid entry. Enter a number between 0 to 1." << endl;
}
}
while (data.preSpread == -1) {
cout << "Enter the precentage spread between the two candidates." << endl;
cin >> data.preSpread;
if (data.preSpread <= 0 || data.preSpread >= 1) {
data.preSpread = -1;
cout << "Invalid input. Enter a number between 0 and 1." << endl;
}
}
}
int main() {
getUserInfo();
return 0;
}
Console:
enter the number of voters
f
Invalid entry, please enter a number larger than zero.
enter the number of voters
Invalid entry, please enter a number larger than zero.
enter the number of voters
Invalid entry, please enter a number larger than zero.
...
...
...
If you write cin >> integervariable but in cin there are character that cannot represent an integer, the input fails, !cin becomes true, and the character remain there until you don't reset the input state from the error and consume the wrong characters.
a proper check can be
while(integervariable has not good value)
{
cout << "prompt the user: ";
cin >> integervariable;
if(!cin) //something wrong in the input format
{
cin.clear(); //clear the error flag
cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); //discard the rubbish
cout << "prompt error message \n";
}
}
Your if statements are always true, you want something more like:
if (data.votingError < 0 || data.votingError > 1) {
...
then data.votingError can take on a value different from -1 and exit your loop.
The std::cin object will check whether or not it is in a valid state every time it reads. If you enter a char where your program expects an int, then you'll "break" the input stream. All subsequent calls to std::cin will then be effectively skipped until you manually reset the input stream. When this happens, you'll never be able to set your values to anything other than -1, and your if statement always evaluates to true, causing an infinite loop.
As an aside, you can check for failure state by including && cin in all of your tests. Input objects implicitly evaluate to true if the stream is in a valid state and to false if the stream is in a failure state instead.