Calling class member from function!

[alex067]

I have an assignment where I have to construct a nonmember function which calls a member function inside it.

The issue lies inside the testSuccesfulSearch function, where I have to call the object "obj" to call the member linearsearch (which is a member function inside class)

the error states: the object has type qualifers that are not compatible with the member function

#include <iostream>
#include <ctime>

using namespace std;

class Myclass
{
private:
	int *ptr; //pointer to 1D dynamic array 
	int size;
public:
	Myclass(int arraySize) //overload constructor 
	{
		size = arraySize;
		ptr = new int[size];
		cout << "Enter data for an array size: " << size << endl;
		for (int i = 0; i < size; i++)
		{
			cin >> ptr[i];
		}
		cout << endl;
	}
	int linearSearch(int searchItem); //linear search 
	~Myclass()
	{
		delete[] ptr;
		cout << "Memory reallocated!" << endl;
	}
};
int Myclass::linearSearch(int searchItem)
{
	srand(time(0));

	int item = searchItem;
	for (int i = 0; i < size; i++)
	{
		if (ptr[i] == item)
		{
			return i;
			break;
		}
	}
	return -1;
}

double testSuccesfulSearch(const Myclass &obj, long int runCount);

int main()
{
	Myclass B(10);
	float average;
	average = testSuccesfulSearch(B, 10000);
	system("PAUSE");
	return 0;
}
double testSuccesfulSearch(const Myclass &obj, long int runCount)
{
	obj.linearSearch(runCount);

}

[booradley60]

The compiler is enforcing const-ness of your object. Notice the addition of const on lines 23 and 30.

#include <iostream>
#include <ctime>

using namespace std;

class Myclass
{
private:
    int *ptr; //pointer to 1D dynamic array 
    int size;
public:
    Myclass(int arraySize) //overload constructor 
    {
        size = arraySize;
        ptr = new int[size];
        cout << "Enter data for an array size: " << size << endl;
        for (int i = 0; i < size; i++)
        {
            cin >> ptr[i];
        }
        cout << endl;
    }
    int linearSearch(int searchItem) const; //linear search 
    ~Myclass()
    {
        delete[] ptr;
        cout << "Memory reallocated!" << endl;
    }
};
int Myclass::linearSearch(int searchItem) const
{
    srand(time(0));

    int item = searchItem;
    for (int i = 0; i < size; i++)
    {
        if (ptr[i] == item)
        {
            return i;
            break;
        }
    }
    return -1;
}

double testSuccesfulSearch(const Myclass &obj, long int runCount);

int main()
{
    Myclass B(10);
    float average;
    average = testSuccesfulSearch(B, 10000);
    system("PAUSE");
    return 0;
}
double testSuccesfulSearch(const Myclass &obj, long int runCount)
{
    obj.linearSearch(runCount);

}

In the function prototype for testSuccessfulSearch, you've stated to the compiler that obj is const. Therefore, the only functions that may be invoked on obj are those that are marked const.

[alex067]

So then do I have to make the object Myclass B constant in order for it to work?

[booradley60]

No, just make the linearSearch function const by adding const in those two places I showed in my last post. What that does is tell the compiler "This method promises not to change the object that invokes it."

[alex067]

Ah interesting, I've never seen the const used like that before. Thank you, the program works fine now, however there is one slight issue left:

My program is intended to take the runcount, initialize it in the linearsearch function, and go through a loop of runcount times, creating a random number each time and searching for that random number in the array.

So for example: if my array consists of 10 integers and my run count is 10000, the loop will initialize 10000 times, creating a random number each time and searching for that said number in the array of 10 integers. If the number is found, I have to increment a counter, and return the counter to find the average number of times that number appeared

However, my program keeps outputting 0

#include <iostream>
#include <ctime>

using namespace std;

class Myclass
{
private:
	int *ptr; //pointer to 1D dynamic array 
	int size;
public:
	Myclass(int arraySize) //overload constructor 
	{
		size = arraySize;
		ptr = new int[size];
		cout << "Enter data for an array size: " << size << endl;
		for (int i = 0; i < size; i++)
		{
			cin >> ptr[i];
		}
		cout << endl;
	}
	int linearSearch(int searchItem) const; //linear search 
	void print();
	~Myclass()
	{
		delete[] ptr;
		cout << "Memory reallocated!" << endl;
	}
};
int Myclass::linearSearch(int searchItem) const
{
	srand(time(0));
	int random;
	int counter = 0;
	for (int i = 1; i <= searchItem; i++)
	{
		for (int j = 0; j < size; j++)
		{
			random = rand() & 10;
			if (ptr[j] == random)
			{
				counter++;
			}
		}
	}
	return counter;
}
void Myclass::print()
{
	for (int i = 0; i < size; i++)
	{
		cout << ptr[i] << " ";
	}
	cout << endl;
}

double testSuccesfulSearch(const Myclass &obj, long int runCount);

int main()
{
	Myclass B(10);
	float average;
	int count;
	count = 10000;
	average = testSuccesfulSearch(B, count);

	cout << "Array size: 10" << endl;
	cout << "Array content: ";
	B.print();

	cout << "Run count: " << count << endl;
	cout << "Average number of comparisons over " << count << " random searches: " << average << endl;



	system("PAUSE");
	return 0;
}
double testSuccesfulSearch(const Myclass &obj, long int runCount)
{
	int comp;
	comp = obj.linearSearch(runCount);
	return float(comp / runCount); //cast 
}