Program to find sum of elements in a given array

Question

I have to find the elements in a given array, and I found a program in other site, but when I try to interpret the code in my way, I have error.

That is from the other site:

#include <iostream>
using namespace std;

// function to return sum of elements
// in an array of size n
int sum(int arr[], int n)
{
    int sum = 0; // initialize sum

    // Iterate through all elements
    // and add them to sum
    for (int i = 0; i < n; i++)
        sum += arr[i];

    return sum;
}

int main()
{
    int arr[] = { 12, 3, 4, 15 };
    int n = sizeof(arr) / sizeof(arr[0]);
    cout << "Sum of given array is " << sum(arr, n);
    return 0;
}

That's mine:

#include <iostream>
using namespace std;
int Function(int arr[], int Broi)
{
    int suma = 0;
    for (int i = 0; i < Broi; i++) {
        cin >> arr[Broi];
        suma += arr[i];
    }
    return suma;
}

int main()
{
    int arr;
    int Broi = sizeof(arr) / sizeof(arr[0]);
    cout << "Srednoto Aritmetichno e: " << Function(arr[], broi);
    return 0;
}

Also the first programe gives the numbers of the array, but I want the user to cin>> them when u write the length of the arr.

A `std::vector` and push_back would be a much better `c++` solution. — drescherjm, Dec 02 '21 at 18:08
What's the error? A wrong result? That would be because you write to `arr[Broi]` but add `arr[i]`. You don't need to use an array at all. Just read the number into an `int` and add that to `suma`. You aren't using the individual numbers anywhere — Pranav Hosangadi, Dec 02 '21 at 18:09
Then you either have to make a large fixed sized array or dynamically allocate using new and possibly resize by allocating a new dynamic array and copy the contents of the old then swap pointers and remove the old. — drescherjm, Dec 02 '21 at 18:11
The error is: [Error] invalid types 'int[int]' for array subscript — BerryTan, Dec 02 '21 at 18:11
You could do `int arr[1000];` then tell the user that he/she can't add any more after 1000 are used. — drescherjm, Dec 02 '21 at 18:12
Although do you even need an array for this problem? You can sum any number of user inputs without using an array at all. — drescherjm, Dec 02 '21 at 18:13
int Broi = sizeof(arr) / sizeof(arr[0]); On this row gives the mistake where is arr[0] — BerryTan, Dec 02 '21 at 18:14
For your case of 10 inputs you can do this: `const int Broi = 10; int arr[Broi];` and then fix the cin as stated above. — drescherjm, Dec 02 '21 at 18:15
Side note: With an up-to-date compiler you can replace `sizeof(arr) / sizeof(arr[0])` with `std::size(arr)`. Note that for either to work, `arr` must be an array, and that array cannot have [decayed to a pointer](https://stackoverflow.com/questions/1461432/what-is-array-to-pointer-decay) by passing it to a function or performing math on it. — user4581301, Dec 02 '21 at 18:35

score 4 · Answer 1 · answered Dec 02 '21 at 18:36

Your code is not declaring an array at all. It is declaring a single int.

You said in comments that:

The task is to read 10 numbers, and to put them in array

So, you should declare a 10-int array in main() and fill it with user values before passing it to Function(), similar to how the original code was doing. The user input doesn't really belong in Function() to begin with.

Try something more like this instead:

#include <iostream>
using namespace std;

int Function(int arr[], int Broi)
{
    int suma = 0;
    for (int i = 0; i < Broi; i++) {
        suma += arr[i];
    }
    return suma;
}

int main()
{
    int arr[10];

    cout << "Enter 10 numbers: ";
    for(int i = 0; i < 10; ++i){
        cin >> arr[i];
    }

    cout << "The sum is: " << Function(arr, 10);
    return 0;
}

Andreas Wenzel · Answer 2 · 2021-12-02T18:55:24.350

The line arr[Broi] is accessing the array out of bounds, causing undefined behavor, because the array consists only of a single element. Even if it consisted of Broi elements, it would be accessing the array out of bounds, because valid indexes would be 0 to Broi - 1.

In the comments section (but not in the question), you stated that you are supposed to read 10 numbers from the user. If arr were pointing to an array of 10 elements instead of 1 element, then it would make sense to write arr[i] instead of arr[Broi].

The simplest solution to the problem would be to not use arrays at all:

#include <iostream>

constexpr int NUM_INPUTS = 10;

int main()
{
    int input;
    int sum = 0;

    for ( int i = 0; i < NUM_INPUTS; i++ )
    {
        //prompt user for input
        std::cout << "Please enter integer #" << i + 1 << ": ";

        //attempt to read integer from user
        if ( ! ( std::cin >> input ) )
        {
            std::cout << "Input failure!\n";
            return 1;
        }

        //add user input to sum
        sum += input;
    }

    //print sum
    std::cout << "\nThe sum of all numbers is: " << sum << ".\n";

    return 0;
}

However, since you stated in the comments section that you are supposed to use arrays, then you are probably supposed to first read all 10 numbers from std::cin into an array of 10 elements and then calculate the sum afterwards:

#include <iostream>
#include <cstdlib>

constexpr int NUM_INPUTS = 10;

void input_array( int arr[] )
{
    for ( int i = 0; i < NUM_INPUTS; i++ )
    {
        //prompt user for input
        std::cout << "Please enter integer #" << i + 1 << ": ";

        //attempt to read integer from user
        if ( ! ( std::cin >> arr[i] ) )
        {
            std::cout << "Input failure!\n";
            std::exit( EXIT_FAILURE );
        }
    }
}

int calculate_sum( int arr[] )
{
    int sum = 0;

    for ( int i = 0; i < NUM_INPUTS; i++ )
    {
        sum += arr[i];
    }

    return sum;
}

int main()
{
    int arr[NUM_INPUTS];

    //fill array with user input
    input_array( arr );

    //print sum
    std::cout << "\nThe sum of all numbers is: " << calculate_sum( arr ) << ".\n";

    return 0;
}

Both programs have the following output:

Please enter integer #1: 20
Please enter integer #2: 30
Please enter integer #3: 10
Please enter integer #4: 5
Please enter integer #5: 31
Please enter integer #6: 17
Please enter integer #7: 6
Please enter integer #8: 14
Please enter integer #9: 18
Please enter integer #10: 50

The sum of all numbers is: 201.

score 1 · Answer 3 · answered Dec 02 '21 at 19:50

The simple fix without too many complicated features would be like below:

#include <iostream>

int Function( int* const array, const std::size_t elementCount)
{
    int suma { };

    for ( std::size_t idx = 0; idx < elementCount; ++idx )
    {
        std::cin >> array[ idx ];
        suma += array[ idx ];
    }

    return suma;
}

int main( )
{
    int myArray[ 4 ] { };
    int suma = Function( myArray, sizeof( myArray ) / sizeof( *myArray ) );
    std::cout << "Srednoto Aritmetichno e: " << suma << '\n';

    return 0;
}

That's it. You can change the size of myArray to anything that fits onto stack memory.

Program to find sum of elements in a given array

3 Answers3