Need advice with my average calculator code - c++

Question

Good day,
I need help with my below code. I have a problem with calculating the average.
The code works as it should expect for calculating the average of the second entry.
I have highlighted the average that does not add up in the below picture. Its weird that the average is only not adding up on the second entry?
#include <iostream>
using namespace std;
float snelheid[][50] = {{}};
float lading[] = {};
float snelheidGem[] = {0};
int ladingNo = 1;
int snelheidToets = 1;
int main()
{
cout << "Hoeveel ladings word getoets?: ";
cin >> ladingNo;
for (int i = 0; i < ladingNo; i++)
{
int n = i + 1;
if (n == 1 || n == 8 || n > 19)
{
cout <<"Wat was die " << n << "st lading?: ";
cin >> lading[i];
cout <<"Hoeveel skote was geskiet vir die "<< n << "st lading?: ";
cin >> snelheidToets;
snelheidGem[i] = {0};
for (int t = 0; t < snelheidToets; t++)
{
int m = t + 1;
if (m == 1 || m == 8 || m > 19)
{
cout <<"Wat was die spoed van die " << m << "st skoot?: ";
cin >> snelheid[i][t];
}
else
{
cout <<"Wat was die spoed van die " << m << "de skoot?: ";
cin >> snelheid[i][t];
}
snelheidGem[i]=snelheidGem[i]+snelheid[i][t];
}
snelheidGem[i] = snelheidGem[i]/snelheidToets;
cout << snelheidGem [i] << endl;
cout << endl;
}
else
{
cout <<"Wat is die " << n << "de lading?: ";
cin >> lading[i];
cout <<"Hoeveel skote was geskiet vir die "<< n << "de lading?: ";
cin >> snelheidToets;
snelheidGem[i] = {0};
for (int t = 0; t < snelheidToets; t++)
{
snelheid[i][t] = {0};
int m = t + 1;
if (m == 1 || m == 8 || m > 19)
{
cout <<"Wat was die spoed van die " << m << "st skoot?: ";
cin >> snelheid[i][t];
}
else
{
cout <<"Wat was die spoed van die " << m << "de skoot?: ";
cin >> snelheid[i][t];
}
snelheidGem[i]=snelheidGem[i]+snelheid[i][t];
cout << snelheid[i][t] << " snelheid" << endl;
cout << snelheidGem[i] << " gemiddeld" << endl;
}
snelheidGem[i] = snelheidGem[i]/snelheidToets;
cout << snelheidGem [i] << endl;
cout << endl;
}
}
return 0;
}
Average calculation

Answer 1

On this line:
float snelheidGem[] = {0};
you are creating an array of size 1, but are then indexing elements such as snelheidGem[1], and snelheidGem[2], etc, which invokes undefined behavior (UB). UB means anything can happen, including giving the correct average sometimes, but not at other times.
You can give it a sufficiently large size:
float snelheidGem[50] = {0};
or much better, use a std::vector, to which you can add elements by doing push_back.
Note that you have the same issue with:
float lading[] = {};