Exercise about loops and arrays - use loops 1 time and how to get the max value of an array

Question

I know just a little about programming but I'm pretty new to C++. I just started to study it one week ago and I'm posting a question about the code I wrote since I can't solve few small problems.

The program I wrote asks how many elements you'd like to analyze and it returns the sum of the elements, how many even and odd numbers you inserted, the sum of the odd and even numbers only and it should returns the maximum (and minimum) value.

This is the code:

#include <iostream>
using namespace std;

int elements, sum = 0, x, arr[10], even = 0, odd = 0, evenSum = 0, oddSum = 0,
        mx; //Variable declaration

int main() {

    cout << "Type how many elements you would like to sum and analyze" << endl; //Input of the numbers of elements to analyze
    cin >> elements;

    if (elements > 10)
        cout << "Too many elements" << endl; //If the elements are more than 10, the program quit
    else {
        for (x = 1; x <= elements; x++) {
            cout << "Type the element number " << x << endl; //Input of elements to assign to the array
            cin >> arr[x];
        }
        for (x = 1; x <= elements; x++) { //Sum of the elements of the array
            sum += arr[x];
        }
        mx = arr[0];
        for (x = 1; x <= elements; x++) { //Find the maximum value of the array
            if (arr[0] >= mx) {
                mx = arr[0];
            }
        }
        for (int x = 1; x <= elements; x++) { //Count and sum of the even elements
            if (arr[x] % 2 == 0) {
                even++;
                evenSum += arr[x];
            }
            if (arr[x] % 2 != 0) { //Count and sum of the odd elements
                odd++;
                oddSum += arr[x];
            }
        }
        cout << "The sum of the elements of the array is: " << sum << endl; //Outputs
        cout << "The max value of the array is: " << mx << endl;
        cout << "Even numbers are: " << even << endl;
        cout << "Odd numbers are: " << odd << endl;
        cout << "The sum of even numbers is: " << evenSum << endl;
        cout << "The sum of odd numbers is: " << oddSum << endl;
    }
    return 0;
}

My questions are:

1. Do I have to repeat the "for" loop 4 times or, since the conditions of the loops are the same, I can write it only one time followed by the code to execute?
2. To calculate the maximum value, I used as a variable name "max" but the editor doesn't compile. I changed the name from "max" to "mx" and it compiles. Is "max" a reserved word for C++? What is wrong?
3. Why the program always gives "0" as the maximum value of the array? I can't understand what is wrong in the algorithm and I can get the maximum value of the listed elements.

Thank you very much for the support. Matteo

Answer 1

1. You should be able to calculate everything inside a single for-loop, yes.

2. This might be because you have the line

   using namespace std;

   at the top of your file. When you write max the compiler assumes that you mean the function std::max: http://en.cppreference.com/w/cpp/algorithm/max

   You could try removing the using namespace std; and instead insert std:: where needed, e.g. std::cin, std::cout and std::endl.

3. There are two problems. First of all you have typos here:

   if (arr[0] >= mx) {, mx = arr[0];

   Replace 0 with x. The second problem occurs if you only enter negative numbers. You don't have an explicit initialization for mx, so it will be initialized to zero. If you only enter negative numbers then your program will incorrectly say that zero is greatest number. You should probably initialize mx to the lowest possible number for its type, e.g.: std::numeric_limit<int>::min().

Answer 2

Code cleansing 101:

There are several things to make your code much cleaner.

1) You don't need that many for loops and since you don't need that many for loops you can get rid of your array.

2) Your variables should be local not global.

3) Several of your variables were not initialized to 0 thus you can't do odd++; (for example)

Look through my changes, understand them, read the comments, and ask questions if you have them :)

#include <iostream>
using namespace std; //probably don't want to use this here

int main() 
{
    // keep these variables local instead of global    
    int elements, sum , even, odd, evenSum, oddSum, mx;
    sum = even = odd = evenSum = oddSum = mx = 0;  //set them all to 0

    cout << "Type how many elements you would like to sum and analyze" << endl; //Input of the numbers of elements to analyze
    cin >> elements;

    if (elements > 10)
        cout << "Too many elements" << endl; //If the elements are more than 10, the program quit
    else 
    {
        // An array is based on the 0 index not the 1 index.
        // so the first value in array as at x = 0 and the second is at x = 1 and so on
        int currentNum;
        for (int x = 0; x < elements; x++) //int x = 0 and x < elements
        {
            cout << "Type the element number " << x << endl; //Input of elements to assign to the array
            cin >> currentNum;
            sum += currentNum;
            if (currentNum >= mx) 
                mx = currentNum;
            if (currentNum % 2 == 0) 
            {
                even++;
                evenSum += currentNum;
            }
            if (currentNum % 2 != 0) { //Count and sum of the odd elements
                odd++;
                oddSum += currentNum;
            }
        }

        cout << "The sum of the elements of the array is: " << sum << endl; //Outputs
        cout << "The max value of the array is: " << mx << endl;
        cout << "Even numbers are: " << even << endl;
        cout << "Odd numbers are: " << odd << endl;
        cout << "The sum of even numbers is: " << evenSum << endl;
        cout << "The sum of odd numbers is: " << oddSum << endl;
    }
    return 0;
}

Answer 3

First, if you have index based-0, you don't read arr[0] in first loop

for (x = 1(error, it should be 0); x <(only '<') elements; x++) {
        cout << "Type the element number " << x << endl; //Input of elements to assign to the array
        cin >> arr[x];
    }

Now, you can do all in two loops.

#include <iostream>
using namespace std;

int elements, sum = 0, x, arr[10], even = 0, odd = 0, evenSum = 0, oddSum = 
0,
    mx; //Variable declaration

int main() {

cout << "Type how many elements you would like to sum and analyze" << endl; //Input of the numbers of elements to analyze
cin >> elements;

if (elements > 10)
    cout << "Too many elements" << endl; //If the elements are more than 10, the program quit
else {
    for (x = 0; x < elements; x++) {
        cout << "Type the element number " << x << endl; //Input of elements to assign to the array
        cin >> arr[x];
    }
    mx = arr[0];
    for (x = 0; x < elements; x++) { //Find the maximum value of the array
        sum += arr[x];
        if (arr[x] >= mx) {
            mx = arr[x];
        }
        if (arr[x] % 2 == 0) {
            even++;
            evenSum += arr[x];
        }
        if (arr[x] % 2 != 0) { //Count and sum of the odd elements
            odd++;
            oddSum += arr[x];
        }
    }

    cout << "The sum of the elements of the array is: " << sum << endl; //Outputs
    cout << "The max value of the array is: " << mx << endl;
    cout << "Even numbers are: " << even << endl;
    cout << "Odd numbers are: " << odd << endl;
    cout << "The sum of even numbers is: " << evenSum << endl;
    cout << "The sum of odd numbers is: " << oddSum << endl;
}
return 0;

}

Alto you can do all in one loop

#include <iostream>
using namespace std;

int elements, sum = 0, x, arr[10], even = 0, odd = 0, evenSum = 0, oddSum = 
0,
    mx; //Variable declaration

int main() {

cout << "Type how many elements you would like to sum and analyze" << endl; //Input of the numbers of elements to analyze
cin >> elements;

if (elements > 10)
    cout << "Too many elements" << endl; //If the elements are more than 10, the program quit
else {
    mx = arr[0];
    for (x = 0; x < elements; x++) {
        cout << "Type the element number " << x << endl; //Input of elements to assign to the array
        cin >> arr[x];

        sum += arr[x];
        if (arr[x] >= mx) {//error here, you need compare arr[x], not arr[0]
            mx = arr[x];
        }
        if (arr[x] % 2 == 0) {
            even++;
            evenSum += arr[x];
        }
        if (arr[x] % 2 != 0) { //Count and sum of the odd elements
            odd++;
            oddSum += arr[x];
        }
    }

    cout << "The sum of the elements of the array is: " << sum << endl; //Outputs
    cout << "The max value of the array is: " << mx << endl;
    cout << "Even numbers are: " << even << endl;
    cout << "Odd numbers are: " << odd << endl;
    cout << "The sum of even numbers is: " << evenSum << endl;
    cout << "The sum of odd numbers is: " << oddSum << endl;
}
return 0;

}

Answer 4

Good point about the array indexing! I know an array is 0-indexed but even starting from 1 the program works fine! I type 5 as a number of elements to analyze and a I can insert, for instance, 1 2 3 4 5, having the correct outputs:

• Sum: 15
• Odd elements: 3
• Even elements: 2

I can't understand why!