How to calculate mean using calling function in C++?

Question

The functions are getInputN(), calculateMean() & displayData().

So to be really clear, these are the requirements.

• getInputN function: Should accept the number of the value, N as an integer as argument and ask the user to enter the value of N number. Then, return the sum of the value as a double.
• calculateMean function: Should accept the number of the value, N and sum of the value as arguments. Then return the mean as a double.
• displayData function: Should accept the mean as argument. Then, display them in the appropriate message on screen. No return value required for this function.

If I run the code, it will display Average = inf

p/s: I'm really sorry for the confusing question at first. I'm really new to this website and this is my very first question. It took me some times to figure out things to ask properly in this platform. I hope you guys understand and once again, sorry for the inconvenience. Thank you for the helps too :)

Here is my code:

#include <iostream>
using namespace std;

int getInputN(int n);
float calculateMean (int n, float sum);
float displayData(double mean);

int i,n;
float sum = 0.0, num[50];
double mean;

int main()
{
    getInputN(n);
    calculateMean (n, sum);
    displayData(mean);

    return 0;
}

int getInputN(int n)
{
    int i;
    float num[50];

    //User enter the number of value
    cout << "Enter the numbers of data: ";
    cin >> n;
    
    //if user input more than 50 numbers
    while (n > 50 || n <= 0)
    {
        cout << "Invalid! Enter the number in range of (1 to 50)." << endl;
        cout << "Enter the number of data: ";
        cin >> n;
    }

    for(i = 0; i < n; ++i)
    {
        cout << i + 1 << ". Enter number: ";
        cin >> num[i];
        sum += num[i];
    }

    return n;
}

    //function to calculate the mean
    float calculateMean (int n, float sum)
    {
    
        mean = sum/n;
    
        return mean;
    }

    //function to display the mean
    float displayData (double mean)
    {
        cout << "Average = " << mean;
    }

Answer 1

The argument int n in the function getInputN is shadowing (hiding) the global variable n. This prevents the global variable from being updated and sum is divided by zero (the default value of gloval variable without explicit initialization).

If you want to pass data using gloval variables, the arguments should be removed because one of that (n as descrived above) is harmful and other are redundant.

Also the function displayData is declared to return float but didn't execute any return statement. This invokes undefined behavior. I fixed this by changing its return type to void.

#include <iostream>
using namespace std;

int getInputN();
float calculateMean ();
void displayData();

int i,n;
float sum = 0.0, num[50];
double mean;

int main()
{
    getInputN();
    calculateMean ();
    displayData();

    return 0;
}

int getInputN()
{
    int i;
    float num[50];

    //User enter the number of value
    cout << "Enter the numbers of data: ";
    cin >> n;
    
    //if user input more than 50 numbers
    while (n > 50 || n <= 0)
    {
        cout << "Invalid! Enter the number in range of (1 to 50)." << endl;
        cout << "Enter the number of data: ";
        cin >> n;
    }

    for(i = 0; i < n; ++i)
    {
        cout << i + 1 << ". Enter number: ";
        cin >> num[i];
        sum += num[i];
    }

    return n;
}

//function to calculate the mean
float calculateMean ()
{

    mean = sum/n;

    return mean;
}

//function to display the mean
void displayData ()
{
    cout << "Average = " << mean;
}

This fix will make the code work, but there should be better design without usage of global variables. References is useful to have functions modify things given as arguments and std::vector is useful to return "arrays".

Answer 2

The variable n in int getInputN(int n) is used in the function instead of the global n declared. As such, using global n (which is uninitialized till that point initialized to 0) to calculate mean = sum/n will lead to a undefined behavior divide by 0 error, resulting in inf.

More info :

• Uninitialized variable behaviour in C++

• C++ global and local variables

Also, the function float displayData (double mean) doesn't return any value, causing another undefined behavior.

More info :

• Why does flowing off the end of a non-void function without returning a value not produce a compiler error?

Modified code :

#include <iostream>
using namespace std;

void getInputN();
void calculateMean();
void displayData();

int i,n;
float sum = 0.0, num[50];
double mean;

int main()
{
    getInputN();
    calculateMean();
    displayData();

    return 0;
}

void getInputN()
{
    int i;
    float num[50];

    //User enter the number of value
    cout << "Enter the numbers of data: ";
    cin >> n;

    //if user input more than 50 numbers
    while (n > 50 || n <= 0)
    {
        cout << "Invalid! Enter the number in range of (1 to 50)." << endl;
        cout << "Enter the number of data: ";
        cin >> n;
    }

    for(i = 0; i < n; ++i)
    {
        cout << i + 1 << ". Enter number: ";
        cin >> num[i];
        sum += num[i];
    }
}

//function to calculate the mean
void calculateMean ()
{
    mean = sum/n;
}

//function to display the mean
void displayData ()
{
    cout << "Average = " << mean;
}

Result :

Enter the numbers of data: 3
1. Enter number: 1
2. Enter number: 3
3. Enter number: 6
Average = 3.33333

Furthermore, if you don't use the numbers for anything else, declaring a float num[50]; is quite pointless. Also, noted that using global variable and using namespace std; is not recommended.

#include <iostream>

const int maxn = 50;
const int minn = 1;

int main()
{
    int n; std::cout << "Enter N : "; std::cin >> n;
    while (n < minn || n > maxn) {std::cout << "Invalid. Re-enter N : "; std::cin >> n;}

    double sum = 0; int tmp;
    for (int i = 0; i < n; i++) { std::cout << "Enter number " << i+1 << " : "; std::cin >> tmp; sum += tmp;}

    std::cout << "Average : " << sum/n;
}

Result :

Enter N : 3
Enter number 1 : 25
Enter number 2 : 97
Enter number 3 : 111
Average : 77.6667

Answer 3

Knowing how the functions are behaved, we can write implementations that work nicely and don't use any global variables at all.

#include <iostream>

double getInputN(int n);
double calculateMean(int n, double sum);
void displayData(double mean);

int main()
{   
    //User enter the number of value
    int numEntries;
    std::cout << "Enter the numbers of data: ";
    std::cin >> numEntries;

    //if user input more than 50 numbers
    while (numEntries > 50 || numEntries <= 0)
    {
        std::cout << "Invalid! Enter the number in range of (1 to 50)." << std::endl;
        std::cout << "Enter the number of data: ";
        std::cin >> numEntries;
    }

    // Get user input
    double sum = getInputN(numEntries);

    double mean = calculateMean(numEntries, sum);

    displayData(mean);

    return 0;
}

double getInputN(int n)
{
    double sum = 0.;

    for (int i = 0; i < n; ++i)
    {
        double userInput;
        std::cout << i + 1 << ". Enter number: ";
        std::cin >> userInput;
        sum += userInput;
    }

    return sum;
}

//function to calculate the mean
double calculateMean(int n, double sum)
{

    double mean = sum / n;

    return mean;
}

//function to display the mean
void displayData(double mean)
{
    std::cout << "Average = " << mean;
}

Let's go into some more detail on each of the changes.

First, I've changed the signatures of all of your functions. getInputN is supposed to return a double, not an int. calculateMean is supposed to accept and return a double, not a float. And displayData isn't required to return anything, it doesn't make sense for it to return anything, and therefore I've made its return type void.

Second, note that I've moved the code for figuring out how many entries to enter from getInputN into main. The reason for this is that the sole argument to getInputN is "how many inputs should we get?", so we need to know its value before we call getInputN.

Third, note how I've used the return values from each function in the calling code. In main, when I write double sum = getInputN(numEntries);, that declares a variable sum and stores the return value of getInputN(numEntries) to sum. When you just write getInputN(n);, the return value from getInputN is discarded. By storing it in a variable in main, I can then pass its value to another function, like in the next line where I've written double mean = calculateMean(numEntries, sum);.

Fourth, note how the requirements of the question are such that I no longer use any kind of array whatsoever. getInputN doesn't bother tracking each individual entry, because all we care about is the final sum at the end.