My cin statement wont work and keeps repeating. | Together C & C++ | Page 1

keen zodiac Oct 17, 2022, 12:26 AM

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Heres the question and expected output:

Heres the error im getting:

Heres my code:

// list of libraries
#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
#include "STACKPAC.h"
using namespace std;

//all function prototypes

//main function
int main()
{
    int value, x, y, r;
    int tom, jerry, mickey;

    Stack<int, 10> p;
    p.clearStack();
    cout << "Enter a postfix expression: ";

    string id;
    while (cin >> id, id != "$")
    {
        //chech whether the input is a number 
        //. If it is, then convert it to its 
        //numeric value
        if (isdigit(id[0]))
        {
            value = stoi(id);
            p.pushStack(value);
        }

        if (id == "tom")
        {
            cout << "Enter the value of tom: "; cin >> tom;
            p.pushStack(tom);
        }
        else if (id == "jerry")
        {
            cout << "Enter the value of jerry: "; cin >> jerry;
            p.pushStack(jerry);
        }
        else if (id == "mickey")
        {
            cout << "Enter the value of mickey: "; cin >> mickey;
            p.pushStack(mickey);
        }
        else if (id == "+")
        {
            x = p.popStack();
            y = p.popStack();
            r = y + x;
            p.pushStack(r);
        }
        else //if (id=="*")
        {
            x = p.popStack();
            y = p.popStack();
            r = y * x;
            p.pushStack(r);
        }
    }
    //pop the stck to see the result
    cout << "\tValue of the expression is: " << p.popStack() << endl;
    system("pause");
    return 0;
}

zealous dawnBOT Oct 17, 2022, 12:26 AM

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keen zodiac Oct 17, 2022, 12:26 AM

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Heres the question and expected output:

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Heres the error I get when running my code:

faint pine Oct 17, 2022, 3:18 AM

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didn't look through the whole thing

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but sometimes you have to clear the buffer for cin

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might be less of a hassle to just do a getline

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and break the input up yourself

keen zodiac Oct 17, 2022, 3:29 AM

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faint pine might be less of a hassle to just do a getline

how would i do this?

faint pine Oct 17, 2022, 3:43 AM

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delimit by space

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anything that's not a digit or operator has it's own cin, like you were doing

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then every time you run into an operator you pop out the two operands

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on which you're going to perform the operation

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it is saying explicitly tom jerry mickey

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but it should be able to be arbitrary

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one temp string

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that you convert into a value and push onto the stack

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in that case its

stack:
7
7, 10
+ pulls them out and pushes 17 onto stack
17, 2, 23 on the stack 
* pulls out last two, 2 and 23 and multiplies them for 46
17, 46 on the stack
- pulls them both out and you get -29

keen zodiac Oct 17, 2022, 3:47 AM

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faint pine that you convert into a value and push onto the stack

im ngl im a beginner so i have no idea what u mean

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is it possible for u to do it by editing my code?

faint pine Oct 17, 2022, 3:54 AM

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  string x = "who are you $";
  while (x.find(" ") != string::npos) {
    int index = x.find(" ");
    string temp = x.substr(0, index);
    cout << temp << endl;
    x.erase(0, index + 1);
  }

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this would pull out

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who

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are

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you

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and outside of the while loop

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all that would be left is $

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so now instead of x = "hardcoded string"

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you would do

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getline(cin, x)

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and you push/pop and operate on the stack as you extract each delimited piece of the string

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a delimiter is just how you split something

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in our case " " is the delimiter

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a single space

keen zodiac Oct 17, 2022, 3:57 AM

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so instead of using cin >> tom i use getline(cin, tom)?

faint pine Oct 17, 2022, 3:57 AM

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i'd make it a string

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not an int

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getline(cin, stringvariable)

keen zodiac Oct 17, 2022, 3:57 AM

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ok and then how do i make the string an int varuable?

faint pine Oct 17, 2022, 3:57 AM

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in that code snippet i sent

keen zodiac Oct 17, 2022, 3:57 AM

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using stoi?

faint pine Oct 17, 2022, 3:58 AM

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as you extract each piece of the string

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if it's not a digit

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or an operator like + - * /

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or w/e

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it means it's going to be a variable

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so you'll have an if branch

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if this piece of the string isn't a number or operator

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ask them to cin >> an int

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and push that onto the stack

keen zodiac Oct 17, 2022, 3:58 AM

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oh so u want me to use that instead of while(cin >> id, id != $)

faint pine Oct 17, 2022, 3:59 AM

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yeah i think that there is just some weird stuff around cin/cout

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where you get \n caught in the buffer

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so if you don't cin.ignore it

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at the right time

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you'll get those annoying loops

keen zodiac Oct 17, 2022, 3:59 AM

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thats what i was thinking

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so is there a way to cin.ignore() it>

faint pine Oct 17, 2022, 3:59 AM

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you might even want to do a cin ignore

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after the getline

keen zodiac Oct 17, 2022, 3:59 AM

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i tried it but i still get the same error

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ok

faint pine Oct 17, 2022, 4:00 AM

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the problem is

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if you cin ignore immediately

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you're only extracting one piece of the string

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right

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so if it's tom jerry bla bla

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and you pull in tom

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then cin ignore

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you're going to erase the rest of the buffer

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there's probably a way to do it your way

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i'm just too lazy to think about it

keen zodiac Oct 17, 2022, 4:03 AM

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so for
string x = "who are you $";
while (x.find(" ") != string::npos) {
int index = x.find(" ");
string temp = x.substr(0, index);
cout << temp << endl;
x.erase(0, index + 1);
}

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it finds the spaces in the string then gets the first part then erases that then gets the next part right?

faint pine Oct 17, 2022, 4:04 AM

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yes

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so you load up everything up to the space into temp

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then you would check what temp is

keen zodiac Oct 17, 2022, 4:04 AM

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so where would i put my parrt of the code in?

faint pine Oct 17, 2022, 4:05 AM

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so every time you pull out a number i.e.,

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every part of the string is a digit

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you stoi it

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and push it onto the stack

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every time you get an operator

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you pop out the last two things on the stack and apply the operation

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if you get anything else

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that means its one of those variables

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like tom jerry mickey w/e

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so you would say

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cout << "Enter a value for " << temp << ": " << endl;
cin >> numToPushToStack (obviously make sure theyre giving you a valid int)

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now technically since you aren't going to be cin'ing anymore strings

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i think you may not even need a cin ignore

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and if you do

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it's just after the first getline

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it doesn't have to be tom

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so first you check if its a number

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then if it's an operator

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anything else is a "variable"

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that the user has to put in

keen zodiac Oct 17, 2022, 4:08 AM

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string x = "who are you $";
while (x.find(" ") != string::npos) {
int index = x.find(" ");
string temp = x.substr(0, index);
if (temp == "tom")
{
cout << "Enter value of tom: "; cin >> tom;
p.pushStack(tom);
}
x.erase(0, index + 1);
}

faint pine Oct 17, 2022, 4:08 AM

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so they can pick their own names

keen zodiac Oct 17, 2022, 4:08 AM

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would this work?

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for only tom

faint pine Oct 17, 2022, 4:08 AM

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pseudo code

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one sec

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while x find " " not npos bla bla
  if tempstring is number
    stoi and push on stack
  else if tempstring is operator
    pull out last two numbers in stack and apply operator, and push the result onto stack
  else
    tempint;
    cout << "Enter value for << temp << ": " << endl;
    cin >> tempint;
    push tempint onto stack

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so in this case

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if the string was

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10 20 + banana * $

----------
10 goes on stack
20 goes on stack
+ pulls them both out adds them to 30 and adds it to stack (now the stack just has a 30 in it
your code now sees banana, which isn't a number or operator
you say "Enter a value for banana: " 
cin >> tempint
push tempint on stack
* pulls out whatever number they put in and 30 and multiplies them giving you your final result

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in this case, you don't have to use words like "tom" or "jerry" or "banana" explicilty

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the user picks whatever dumb names they want

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when they put in the postfix expression

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does that make sense?

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now when you exit the while loop, the last thing you pop out of the stack should be the final result

keen zodiac Oct 17, 2022, 4:16 AM

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kinda but not really

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cus im trying to do it as close as i can to the example i was given

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which is similar to the initial clode i sent

faint pine Oct 17, 2022, 4:17 AM

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yeah but it says "suppose an expression was given"

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then it gives sample input

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it feels like the assumption is

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that you don't necessarily want to just handle that specific case

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with tom jerry and mickey

keen zodiac Oct 17, 2022, 4:17 AM

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thats what i t hought at first too

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but its actually specifically tom and jerry and mickey

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cus he wants me to somehow cin if tom is in the expression

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otherwise dont ask for tom

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it makes more sense that way cus its similar to the examples given

faint pine Oct 17, 2022, 4:19 AM

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i mean, you can do it that way then if you want

keen zodiac Oct 17, 2022, 4:19 AM

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do u know how to fix the issue im having with my way?

keen zodiac Oct 17, 2022, 4:37 AM

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#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
#include "STACKPAC.h"
using namespace std;

//all function prototypes

//main function
int main()
{
    int value, x, y, r;
    int tom, jerry, mickey;
    string id;

    Stack<int, 10> p;
    p.clearStack();
    cout << "Enter a postfix expression: ";
    cin >> id;
    while (id.find(" ") != -1) 
    {
        int index = id.find(" ");
        string temp = id.substr(0, index);
        cout << temp << endl;
        id.erase(0, index + 1);
    }
    cout << "\tValue of the expression is: " << p.popStack() << endl;
    system("pause");
    return 0;
}

@faint pine why doesnt this work?

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i tested it to print out temp cout << temp

faint pine Oct 17, 2022, 4:40 AM

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what is it doing

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also you're doing cin and not getline

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@keen zodiac

keen zodiac Oct 17, 2022, 4:44 AM

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#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>
#include "STACKPAC.h"
using namespace std;

//all function prototypes

//main function
int main()
{
    int value, x, y, r;
    int tom, jerry, mickey;
    string id;

    Stack<int, 10> p;
    p.clearStack();
    cout << "Enter a postfix expression: ";
    getline(cin, id);
    while (id.find(" ") != -1) 
    {
        int index = id.find(" ");
        string temp = id.substr(0, index);
        if (isdigit(temp[0]))
        {
            value = stoi(temp);
            p.pushStack(value);
        }
        if (temp == "tom")
        {
            cout << "Enter the value of tom: "; cin >> tom;
            p.pushStack(tom);
        }
        else if (temp == "jerry")
        {
            cout << "Enter the value of jerry: "; cin >> jerry;
            p.pushStack(jerry);
        }
        else if (temp == "mickey")
        {
            cout << "Enter the value of mickey: "; cin >> mickey;
            p.pushStack(mickey);
        }
        else if (temp == "+")
        {
            x = p.popStack();
            y = p.popStack();
            r = y + x;
            p.pushStack(r);
        }
        else //if (id=="*")
        {
            x = p.popStack();
            y = p.popStack();
            r = y * x;
            p.pushStack(r);
        }
        id.erase(0, index + 1);
    }
    cout << "\tValue of the expression is: " << p.popStack() << endl;
    system("pause");
    return 0;
}

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@faint pine i replaced cin with getline and tested it and it got the correct values for temp

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now this is the full code and it doesnt output the right value

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it gives like -1294381347

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tom jerry + mickey 23 * - $

faint pine Oct 17, 2022, 5:26 AM

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you're not handling -

wind yarrow Oct 17, 2022, 4:24 PM

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keen zodiac Heres the question and expected output: Heres the error im getting: Heres my ...

when there is nothing left to read from cin, trying to read from cin will activate the error flags of the ifstream object cin, trying to read from cin when there are error flags active results in nothing getting read at all, meaning that $ will never be read, meaning that you get an infinite while loop

zealous dawnBOT Oct 18, 2022, 5:21 AM

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#My cin statement wont work and keeps repeating.