Average of even numbers divisible by 3 c ,I don't understand why the code is running wrong-CodePudding

I need help finding the error in this code. It's supposed to find the average of the input numbers that are not divisible by 2 or 3.

#include <iostream>
using namespace std;
void enterarray(int a[], int &n) { 
    cout << "please enter n: ";
    cin >> n;
    for(int i = 0; i < n; i  )
        cin >> a[i];
}

double average(int a[100], int n)
{
    int t = 0, count;
    for(int i = 0; i < n; i  )
        if( a[i] % 2 == 0 && a[i] % 3 == 0) {
            t = t   a[i];
            count  ;
        }
    return t * 1.0 / count;
}

int main()
{
    int a[100];
    int n;
    enterarray(a, n);
    cout << average(a, n);
    return 0;
}

CodePudding user response：

count needs to be initialized.

    int t=0, count=0;

n needs to be initialized in main.

int n = 0;

enterarray(int a[], int &n) could do with bounds checking n is less-equal to 100.

CodePudding user response：

The problem is that your count variable is uninitialized and

any uninitialized local/block scope built in type variable has a garbage value.

using(accessing) which can lead to undefined behavior.

The solution would be to initialize count like:

int t = 0, count = 0;

Problem 2: Note also that before dividing t by count you should check that count!=0. That is, if count is zero you could simply return 0 instead of dividing by 0 as i have done in the below shown program.

The below shown program uses std::vector instead of array.

#include <iostream>
#include <vector>
using namespace std;
//the first argument is a vector of int passed by reference
void enterarray(std::vector<int> &a, int &n) { 
    cout<<"please enter n: ";
    cin >> n;
    int elem;
    for(int i=0; i<n; i  ) 
    {
        cin >> elem;
        a.emplace_back(elem);
    }
}
//no need to pass n because we can find the size of the vector using size() member function 
double average(const std::vector<int> &a) {
    int t=0, count = 0;//initialize count and t to 0
    for(const int &element: a){
        std::cout<<element<<std::endl;
        if( element % 2 == 0 && (element % 3 == 0)) {
            t = t   element;
            count  ;
        }
    }
    //make sure you don't divide by zero
    return (count > 0 ?(t * 1.0) / count: 0);
}
int main() {
    //create a vector instead of an array 
    std::vector<int> a;
    
    int n = 0;
    enterarray(a, n);
    
    cout<<average(a);//no need to pass n
    return 0;
}