Error - int 'counter' was not declared in this scope

Question

\main112.cpp    In function 'int main()':
63  36  \main112.cpp    [Error] 'counter' was not declared in this scope
28               \Makefile.win  recipe for target 'main112.o' failed

#include <string>
#include <iostream>
#include <windows.h>
#include <stdlib.h>

using namespace std;

struct Person
{
    string name;
    string race;
    int weight;

    void write();
    void show();
    void check();
};

void Person::show()
{
    cout<<"ÔÈÎ: "<<name<<endl;
    cout<<"Íîìåð ðåéñà: "<<race<<endl;
    cout<<"Âåñ áàãàæà: "<<weight<<endl;
}

void Person::write()
{
    cout<<"Ââåäèòå ÔÈÎ: ";
    getline(cin,name);
    cout<<"Ââåäèòå íîìåð ðåéñà: ";
    getline(cin,race);
    cout<<"Ââåäèòå âåñ áàãàæà: ";
    cin>>weight;
    cin.ignore();
}

void Person::check()
{
    int counter = 0;
    if(weight>10)
    {
        counter++;
    }
}

int main()
{
    SetConsoleCP(1251);
    SetConsoleOutputCP(1251);
    setlocale(0, "Russian");


    Person* persons=new Person[4];
    for (int i = 0; i < 4; i++)
    {
        persons[i].write();
    }
    for (int i = 0; i < 4; i++)
    {
        persons[i].show();
        persons[i].check();
    }
    cout<<"Ñ áàãàæîì áîëüøå 10 êã: "<<counter<<" ÷åëîâåê"<<endl;

    delete[] persons;
    return 0;
}

Program that works the way its coded and should work, without this problem

Homework:

Write a program for processing passenger information. Information includes: 1) Full name of the passenger. 2) Flight number. 3) Luggage weight The program should allow the user to: 1) Read data from the keyboard and display it. 2) Calculate the number of passengers with the weight of baggage which is more than 10 kg

Answer 1

The problem here is you're defining counter in the scope of the function Person::check(). Every time you run the check function a new variable called counter is created set to be the value 0. Then once it's through running that function it ceases to exist.

A quick and dirty way of fixing this would be declaring counter as a global variable.

#include <string>
#include <iostream>
#include <windows.h>
#include <stdlib.h>

using namespace std;

int counter = 0;

struct Person
{
    string name;
    string race;
    int weight;

    void write();
    void show();
    void check();
};

void Person::show()
{
    cout<<"ÔÈÎ: "<<name<<endl;
    cout<<"Íîìåð ðåéñà: "<<race<<endl;
    cout<<"Âåñ áàãàæà: "<<weight<<endl;
}

void Person::write()
{
    cout<<"Ââåäèòå ÔÈÎ: ";
    getline(cin,name);
    cout<<"Ââåäèòå íîìåð ðåéñà: ";
    getline(cin,race);
    cout<<"Ââåäèòå âåñ áàãàæà: ";
    cin>>weight;
    cin.ignore();
}

void Person::check()
{
    if(weight>10)
    {
        counter++;
    }
}

int main()
{
    SetConsoleCP(1251);
    SetConsoleOutputCP(1251);
    setlocale(0, "Russian");


    Person* persons=new Person[4];
    for (int i = 0; i < 4; i++)
    {
        persons[i].write();
    }
    for (int i = 0; i < 4; i++)
    {
        persons[i].show();
        persons[i].check();
    }
    cout<<"Ñ áàãàæîì áîëüøå 10 êã: "<<counter<<" ÷åëîâåê"<<endl;

    delete[] persons;
    return 0;
}

A better way would be defining counter as a member variable of your struct then you can get the value of each of the person objects' counter variable at anytime after declaring the object.

Answer 2

Familiarize yourself with the concept of scope.

Because its scope is the function Person::check, counter is only visible within the bounds of Person::check. No other parts of the program are allowed to interact with it.

Suggested solution:

Change Person::check (and its declaration) to return a boolean. Example:

bool Person::check() const 
{
    return weight>10;
}

The method is declared const to promise that this function will not change the object. This is done to prevent errors and allow a function that should not change the object to be used on a constant Person. This can prevent subtle errors from creeping into the code.

Now a user can check a Persons baggage weight and do with the result of check whatever they want. In the case of main, it wants to keep a count. There is no reason for anyone but main to know what it does, so counter should be scoped by main. eg:

int main()
{
   ...


    int counter = 0;
    for (int i = 0; i < 4; i++)
    {
        persons[i].show();
        if (persons[i].check()) 
        {
            counter++;
        }
    }
    cout<<"Ñ áàãàæîì áîëüøå 10 êã: "<<counter<<" ÷åëîâåê"<<endl;
    ...
}

Side note: There doesn't seem to be a need for persons to be dynamically allocated. Consider replacing

Person* persons=new Person[4];

with

Person persons[4];

and removing

delete[] persons;

If you are dynamically allocating in preparation for a variable number of Persons, prefer to use std::vector

std::vector<Person> persons;

and push_back or emplace_back Persons as they are introduced.

Answer 3

Here's how you fix it. Declare counter in main, make check return bool, and count the number of times it returns false. This encapsulates counter and it makes more sense for check to actually return a Boolean value. Here's what the body of for loop should do:

if (!persons[i].check())
  ++counter

Answer 4

The error message is correct, because there is no counter in main. You only declare counter here:

void Person::check()
{
    int counter = 0;
    if(weight>10)
    {
        counter++;
    }
}

and its scope is limited to that method. Actually each time the function is called you get a new counter which gets initialized to 0.

If instead you make counter a member you can keep its value across multiple calls to the method:

class Person() {
    public:
    int counter = 0;
    int check() {
        if (weight > 10) ++counter;
    }
    // ...other stuff left out
};

I also changed the method to return the value of the counter (otherwise you would have to write a getter or some means to get its value).