I posted an earlier question asking for help with using a validation script in my code. After a very helpful answer I was able to sort of figure out how I needed to proceed. Well, I've hit a big obstacle;
#include <iostream>
#include <sstream>
#include <string>
#include <ctype.h>
using namespace std;
int main()
{
unsigned __int64 input = 0;
int n, i;
char str[]="c3po...";
i=1;
n=0;
for (cout << "Input a number" << endl; cin >> input; cin.ignore(numeric_limits<int>::max(), '\n'))
{
cout << "We're parsing your input '" << input << "'\n";
if (input % 2 == 0)
{
cout << "Even!" << endl;
}
else if (input % 2 == 1)
{
cout << "Odd" << endl;
cout << "Lets make it even shall we? " << "Your new number is... " << input + 1 << endl;
}
else (isalnum(str[i]));i++;
{
cout << "We could not parse '" << input << "' as a number.\n";
}
}
system ("pause");
return 0;
}
As you can see from my code, the validation script is well, sort of working. I have some bugs I wish to iron out.
1- When I input a number, it runs though the code as it should but it also displays
Could not parse 'inputted number' as a number
obviously when a number is inputted you don't want this to happen!
2- For the error message, it is showing the inputted number as [0]. Is this to do with using an integer? How can this be fixed?
Thanks!
your problem is quite simple, you have small mistake on this line
else (isalnum(str[i]));
Your else statement ends at the semicolon and does actually nothing. Following statements will be executed every time.
i++;
{
cout << "We could not parse '" << input << "' as a number.\n";
}
Related
I've started to learn how to code in C++ on my spare time, using different sites and apps that someone who has also learned C++ online provided me with. By now, I know the most basic commands. I've tried an exercise given by a program, and I'm given the information that someone is going on a vacation, and needs to know how much baggage he can bring with him. The limit to how many baggages he can carry is 45, and I have to display a different output if the baggages are below, above or the same as the limit (45 baggages). I have done some coding, and I ended up with this:
#include <iostream>
using namespace std;
int main()
{
const int limit = 45;
int bag;
cout << "Please type your number here: ";
cin >> bag;
string yn;
int keep = 0;
if (limit < bag)
{
cout << "You passed the limit." << endl;
};
if (limit == bag)
{
cout << "Just enough." << endl;
};
if (limit > bag)
{
cout << "You got space." << endl;
};
++keep;
while(keep > 0)
{
int keep = 0;
cout << "Do you want to try another number?" << endl;
cin >> yn;
cout << endl;
if(yn == "yes")
{
int bag = 0;
cout << "Please type your number here: ";
cin >> bag;
if (limit < bag)
{
cout << "You passed the limit." << endl;
};
if (limit == bag)
{
cout << "Just enough." << endl;
};
if (limit > bag)
{
cout << "You got space." << endl;
};
}
else
{
return 0;
}
}
}
I have developed it more than needed -as you can see-, out of my own interest in the problem. I have copied and pasted the 3 IF commands as seen above, and I believe that there is an easier way, with less code, do solve this. What I have thought of is if I could go back and execute some line of code again, either from a line and below (e.g. from line 45 and below), or specific lines of code (e.g. from line 45 to line 60).
I would appreciate it if you thought of another way to solve this problem and posted your code below.
Thank you for your reply.
We all started writing our first C++ program at some time, so allow me to give you some additional feedback:
First of all, avoid writing using namespace std;
Secondly, naming - what is bag, limit, keep and yn? Wouldn't it be much easier to read and understand if they were called bagSize, maximumPermittedBagSize, inputFromUser (you don't really need the variable keep, see below)?
Finally, here is a (roughly) refactored version your program, with duplication removed and comments added.
#include <iostream>
int main()
{
const int maximumPermittedBagSize = 45;
// Loops forever, the user exits by typing anything except 'yes' laster
while(true)
{
std::cout << "Please type your number here: " << std::endl;
//Declare (and initialize!) variables just before you need them
int bagSize = 0;
std::cin >> bagSize;
if (bagSize > maximumPermittedBagSize)
{
std::cout << "You passed the limit." << std::endl;
}
else if (bagSize == maximumPermittedBagSize )
{
std::cout << "Just enough." << std::endl;
}
else
{
std::cout << "You got space." << std::endl;
}
std::cout << "Do you want to try another number?" << std::endl;
std::string inputFromUser = "";
std::cin >> inputFromUser;
std::cout << std::endl;
//Leave the loop if the user does not answer yes
if(inputFromUser != "yes")
{
return 0;
}
}
}
You can simply run a while loop and do like this:
#include <iostream>
using namespace std;
int main()
{
const int limit = 45;
int bag;
string yn = "yes";
while(yn == "yes")
{
cout << "Please type your number here: ";
cin >> bag;
if (limit < bag)
{
cout << "You passed the limit." << endl;
}
else if (limit == bag)
{
cout << "Just enough." << endl;
}
else if (limit > bag)
{
cout << "You got space." << endl;
}
cout << "Do you want to try another number?" << endl;
cin >> yn;
cout << endl;
}
}
The idea behind this code in c++ is to calculate the sum of all the entered numbers. When the user enters 0, the program should stop. This part of the code is working as I intended, but I'd like to include a variant which recognizes that a character different than a float number has been entered, ignore it in the calculation and allow the user to continue entering float numbers. At the moment, entering anything else but a float number stops the program.
I know there's a "if (!(cin >> numb))" condition, I've tried parsing it in different places in the code, but I can't figure out how to force the program to ignore these invalid inputs. I would be very grateful for any help.
#include <iostream>
#include <stdlib.h>
using namespace std;
float numb; float sum=0;
int main()
{
cout << "This app calculates the sum of all entered numbers." << endl;
cout << "To stop the program, enter 0." << endl << endl;
cout << "Enter the first number: ";
cin >> numb;
while(true)
{
sum += numb;
if (numb!=0)
{
cout << "Sum equals: " << sum << endl << endl;
cout << "Enter another number: ";
cin >> numb;
}
else
{
cout << "Sum equals: " << sum << endl << endl;
cout << "Entered 0." << endl;
cout << "Press Enter to terminate the app." << endl;
exit(0);
}
}
return 0;
}
You have three options:
trial and error: try to read a float, and in case of error clear the error flag, ignore the bad input and read again. The problem is that you don't know really how many of the input is to be ignored.
read strings: read space delimited strings, try to convert the string using stringstream, and just ignore the full string in case of error. The problem is that if the input starts with a valid float but then contains invalid characters (e.g. 12X4), the invalid part will be ignored (e.g. X4)
control parsing: read space delimited strings, try to convert the string using std::stof(), and check that all characters of the string where successfully read
Here the second approach, with a slightly restructured loop, so that a 0 entry will lead to exiting the loop and not the full program:
string input;
while(cin >> input)
{
stringstream sst(input);
if (sst>>numb) {
sum += numb;
cout << "Sum equals: " << sum << endl << endl;
if (numb==0)
{
cout << "Entered 0." << endl;
break; // exits the while loop
}
cout << "Enter another number: ";
}
else
{
cout << "Ignored entry "<<input<<endl;
}
}
cout << "Press Enter to terminate the app." << endl;
Online demo
If you prefer a more accurate parsing, consider something like:
size_t pos=0;
float xx = stof(input, &pos );
if (pos!=input.size()) {
cout << "error: invalid trailing characters" <<endl;
}
You have to clear the failbit after a failed read. After that, you can read in the invalid stuff into a string (that you just ignore). This function will read in values and add them up until it encounters a 0 or the end of the input stream.
int calc_sum_from_input(std::istream& stream) {
int sum = 0;
// If it couldn't read a value, we just read the thing into here
std::string _ignored;
while(stream) // Checks if the stream has more stuff to read
{
int value;
if(stream >> value)
{
if(value == 0) // Exit if it read the value 0
break;
else
sum += value; // Otherwise update the sum
}
else {
// Clear the failbit
stream.clear();
// Read ignored thing
stream >> _ignored;
}
}
return sum;
}
The logic is basically:
set the initial sum to 0
check if there's stuff to read
if there is, try reading in a value
if successful, check if the value is 0
if it's 0, exit and return the sum
otherwise, add the value to the sum
otherwise, clear the failbit (so that you can read stuff in again) and read the bad value into a string (which gets ignored)
otherwise, return the value
I'm trying to write a program, which shows a custom message in the console when I type load. But I can't seem to get it to work. :/
#include "stdafx.h"
#include "iostream"
#include "string"
using namespace std;
int main()
{
int commands();
string text;
cout << "Write your registered e-mail to continue...\n";
cin >> text;
string input;
cout << "\n";
cout << "Welcome " << text << endl;
cout << "\n";
cout << "www.steamcommunity.com/id/thetraderdazz> ";
cin >> input;
if (input = load);
cout << "loading...";
system("pause");
return 0;
}
It also gives me the following error:
identifier "load" is undefined.
if (input = load);
There are three mistakes with this line. The first is that you used the assignment operator = instead of comparison operator ==. The former assigns, the latter compares.
The second mistake is that you placed a semicolon after the parenthesis, indicating an empty body. Your compiler should have given you a warning about this.
Finally, there is no variable load. You mean to compare to string literal "load".
Fix to
if (input == "load")
cout << "loading...\n";
You probably intended the following
if (input == "load") {
cout << "loading...";
}
So I have to create an AI program than interacts with the user and responds based on the user input. I'm not very experienced, and this has already took hours lmao, I've looked online but I figured I'd actually post my code and try get some help/advice.
Basically the AI helps with maths, I have the program introducing itself and asking what it wants help with but when I enter Addition, Subtraction etc it just responds with numbers when it should respond with "Great, I'll help you with Addition!/(whatever user input)"
Screenshot of first running program: http://prntscr.com/elw7b4
Screenshot after entering what user needs help with: http://prntscr.com/elw7ky
(Obviously it's a bit all over the place at the moment, I did the calculator before anything else hence why it's giving additional results.
The calculator was working before entering the following code: (As you can see http:// prntscr.com /elwavs only two links cos haven't got more than 10 rep)
void Inpsum()
{
cout << "Hello, my name is Eva! I am able to help you with basic Maths! How may I be of Assistance today?" << endl;
float inpsum;
cin >> inpsum;
cout << "Great!, I will help you with " << (inpsum) << endl;
}
but entering the above code broke the calculator.
here is the full code:
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <iomanip>
using namespace std;
//user inputs what he needs help with/program output
void Inpsum()
{
cout << "Hello, my name is Eva! I am able to help you with basic Maths! How may I be of Assistance today?" << endl;
cin >> inpsum;
cout << "Great!, I will help you with " << (inpsum) << endl;
}
//addition function
void Add() {
float add1, add2;
cout << "Please enter two values you want added together" << endl;
cin >> add1;
cin >> add2;
cout << "The answer is: " << (add1 + add2) << endl;
}
//subtraction function
void Subt() {
float subt1, subt2;
cout << "Please enter two values you want subtracted" << endl;
cin >> subt1;
cin >> subt2;
cout << "The answer is: " << (subt1 - subt2) << endl;
}
//division function
void Div()
{
float div1, div2;
cout << "Please enter two values you want divided" << endl;
cin >> div1;
cin >> div2;
cout << "The answer is: " << (div1 / div2) << endl;
}
//multiplication function
void Mult() {
float mult1, mult2;
cout << "Please enter two values you want multiplacted" << endl;
cin >> mult1;
cin >> mult2;
cout << "The answer is: " << (mult1 * mult2) << endl;
}
int main()
{
Inpsum(); //user inputs what they want help with
Add();
Subt();
Div();
Mult();
return 0 ;
}
Basically - I've set the calculator up, and it was working. But upon trying to implement input and output between the user and the program I'm going wrong and have broken everything. Instead of the program saying "Great I'll help you with Addition", it says "Great, I'll help you with -134567432"
I'm not asking for anyone to do it for me, rather point me in the right direction so I can actually know what to do in the future.
Notice you define inpsum using float inpsum;, but what you are trying to store is string, or words. They are not compatible. You can learn something more about data types and strings in C++.
It might help to use an enum since you only have a handful of choices. You could do something like this:
enum class OPERATION : char {
Addition = 'A',
Subtraction = 'S',
Division = 'D',
Multiplication = 'M'
};
Then instead you cin to a string and have the following:
std::string input;
std::cin >> input;
switch(static_cast<OPERATION>(input[0])) {
case OPERATION::Addition:
Add();
break;
case OPERATION::Subtraction:
Subt();
break;
case OPERATION::Division:
Div();
break;
case OPERATION::Multiplication:
Mult();
break;
default:
std::cerr << "Invalid input" << std::endl;
exit(1);
}
Defining the enum will allow you to cast values to it which match its values. This allows you to safely do a switch with defined inputs that you expect to see as your program runs.
Using C++ (g++-4.7 on Mint 16).
Code is a unrefined (and unfinished) Tic-Tac-Toe game.
#include <iostream>
using namespace std;
int main()
{
//initial data
char turn='A';
char ttt[] = {'1','2','3','4','5','6','7','8','9'};
int move;
int over=0; //0 is no, 1 is yes
int valid=0;
while ( over == 0)
{
//display
cout << "\n" << ttt[0] << "|" << ttt[1] << "|" << ttt[2] <<"\n-----\n";
cout << ttt[3] << "|" << ttt[4] << "|" << ttt[5] <<"\n-----\n";
cout << ttt[6] << "|" << ttt[7] << "|" << ttt[8] <<"\n\n Choose a number (Player " << turn << "):";
//ask enter for play with turn
cin >> move;
cout << "\n";
valid = 0;
while (valid == 0)
{
//check if input is valid
if (((move > 0) and (move < 10)) and
((ttt[move-1] != 'A') and (ttt[move-1] != 'B')) and
(cin))
{
ttt[move-1] = turn;
valid=1;
}
else
{
cout << "Invalid slot. Choose a number (Player " << turn << "):";
cin >> move;
cout << "\n";
}
}
//check if done if no //change turn then goto //display
if (((ttt[0]==ttt[1]) and (ttt[1]==ttt[2])) or
((ttt[3]==ttt[4]) and (ttt[4]==ttt[5])) or
((ttt[6]==ttt[7]) and (ttt[7]==ttt[8])) or
((ttt[0]==ttt[3]) and (ttt[3]==ttt[6])) or
((ttt[1]==ttt[4]) and (ttt[4]==ttt[7])) or
((ttt[2]==ttt[5]) and (ttt[5]==ttt[8])) or
((ttt[0]==ttt[4]) and (ttt[4]==ttt[8]))or
((ttt[2]==ttt[4]) and (ttt[4]==ttt[6])))
{
//display winner or say draw
cout << "Player " << turn << " wins!\n";
over=1;
}
else
{
//change turn
if (turn=='A')
{ turn='B';
}
else
{ turn='A';
}
}
}
return 0;
}
There seem to be a bug on the code. On the part where check if input is valid the and (cin) seem to be failing.
When entering a character, (Instead of a number) it output continuously stacks of:
Invalid slot. Choose a number (Player A or B):
I tested the rest of condition without it, it was all working well. Is there a problem on the code or is this really "cin" problem? I've also tried out !(!cin) but it's the same scenario.
You must clear the fail bit from the cin stream in your else block.
When you enter a character that isn't an integer, the cin stream sets the fail bit, which you correctly check for in your if statement, but you never clear it afterward. This causes your input validity check to be false forever.
#include <limits>
...
else
{
cin.clear(); // Add this line
cin.ignore(numeric_limits<streamsize>::max(), '\n'); // And this one
cout << "Invalid slot. Choose a number (Player " << turn << "):";
cin >> move;
cout << "\n";
}
For additional information, see the documentation for std::basic_ios::clear
Update: see this question and this question for similar problems.
Essentially, you also need to tell cin to ignore whatever is in the stream or it will continually set the fail bit with its bad contents you haven't cleared yet. I modified the above snippet to work.