Ok i belive i understand your question now. The first thing that comes into my mind is this:
float ProbSubtraction = 100;
const float Random = FMath::FRandRange(0, 100); // Randomize a number between 0 and 100
for (int32 i = 0 ; i < Items.Num() ; i++) // Loop through all of the items
{
ProbSubtraction = ProbSubtraction - Items[i].Chance; // Subtract the chance
if (Random >= ProbSubtraction ) // Check if the random number is bigger or equal than the subtraction, if it is then that is your item.
{
//Do stuff with your selected item
break; // You need to break the for loop here, or else you'll get the rest of the items as the right one.
}
}
The overall idea is to have a float variable starting at 100 and then you loop through your items array and you keep subtracting the chance and if the random number is bigger or equal to your current subtraction then that’s your item.