Replacing if-cascade on numerical ranges with 3-LOC (using vector + upper_bound)

Grade Compact Calculation.cpp

#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

/*
  Just for fun: equivalent to:
  
  if (score < 40)
    return 'D';
  if (score >= 40 && score<60)
    return 'B';
  if (score >= 60 && score<75)
    return 'A';
  if (score >= 75 && score<90)
    return 'E';
  return 'O';
*/

char grade(int score)
{
    static const vector<int> ranges{40, 60, 75, 90, 100};
    static const vector<char> grades{'D', 'B', 'A', 'E', 'O', 'O'}; // last 'O' is kind of "saturation"
    return grades[distance(begin(ranges), upper_bound(begin(ranges), end(ranges), score))];
}

int main()
{
    cout << grade(0) << endl; // D
    cout << grade(45) << endl; // B
    cout << grade(60) << endl; // A
    cout << grade(100) << endl; // O
}