How To Fix " Error LNK2019 : unresolved external symbol ... "

Question

I tried to make a calculator for midterm and final grades of 5 students. 40% of Midterm and 60% of finals in an array a[5][3]. a[5][3] because 5 students, 3 lines because 1 for midterm another for finals and last one for overall grade(40% of Mid. + 60% of Finals). I get the "error lnk2019". What is wrong with that code? Thanks..

#include "stdafx.h"
#include <iostream>
using namespace std;

float a[5][3];
float data(float x);
float calc(float y);
float HL(float z);

int main()
{
    data(a[5][3]);
    calc(a[5][3]);
    HL(a[5][3]);

    system("pause");
    return 0;
}

float data(float x[5][3])
{
    for (int i = 0; i < 5; i++)//Getting the Grades
    {
        cout << "Enter midterm for St" << i + 1 << " : ";
        cin >> x[i][0];
        cout << "Enter final for St" << i + 1 << " : ";
        cin >> x[i][1];
    }
    return x[5][3];
} 

float calc(float y[5][3])
{
    for (int i = 0; i < 5; i++)//Calc. Overall Grades
    {
        y[i][2] = y[i][0] * 0,4 + y[i][1] * 0,6;
    }
    return y[5][3];
}

float HL(float z[5][3])
{
    float max = 0, min = 0;
    for (int i = 0; i < 5; i++)//Finding Highest and Lowest
    {
        if (z[i][2]>max)
        {
            max = z[i][2];
        }
        if (z[i][2] < min)
        {
            min = z[i][2];
        }
    }
    cout << "The Lowest Grade : " << min << "\nThe Highest Grade : " << max;
    return z[5][3];
}

Answer 1

I suggest you go through a tutorial to brush up on your array basics. http://www.cplusplus.com/doc/tutorial/arrays/

You syntax for calling the functions is incorrect. Also, your functions prototypes do not match.

float data(float x);

and

float data(float x[5][3])
{

Also, when calling the function, don't specify the dimensions.

float someFloat = data( a );

Answer 2

You declared two functions

float data(float x);
float calc(float y);

... and used them a float argument, too (otherwise the compiler would have complained). However, you then defined them with an entirely different signature:

float data(float x[5][3]) { ... }
float calc(float y[5][3]) { ... }

The declarations have entirely different types. While the functions you declared take one float as argument, the functions you defined take a pointer to an array of floats as argument. More precisely, the functions you define take a pointer to an array of 3 floats as arguement as they are equivalent to this declaration:

float data(float (*x)[3]);
float calc(float (*y)[3]);

Answer 3

Also, fix these calls:

data(a[5][3]);
calc(a[5][3]);
HL(a[5][3]);

Because you are referencing an inexistent element in matrix a. Either you'll pass an undefined value, or you will get a segfault.

Remember that the last element of your amatrix is a[4][2]. If your intention was to pass all the matrix to your function, and not a single element, you have to redefine your prototypes and use only the matrix name a as the argument.

The "undefined symbol" the linker refers to are your functions data, calc and HL. The three of them are used in your main() function as functions that expects a single float value to work with. So are your prototypes.

But your implementation uses matrices as arguments, not floats. A C compiler should complain about wrong type argument used in functions data, calc and HL, but a C++ compiler will interpret it as data, calc and HL being overloaded functions, so they may have more than one implementation. You provide one of them (with a matrix as argument), but the compiler needs the other one (with a float as argument). The linker is responsible to find all the used implementations of a overloaded function. As it cannot find them, it throws that error.