Values, expressions, and types

The idea

Start here if you can read simple arithmetic but have not written C++. A complete console program includes the headers it uses and begins its work in main. A declaration gives an object a type and an initial value. Braces make initialization visible, while const prevents later assignment through that name. The compiler checks types before the program runs; a successful compilation does not prove the calculation matches your intention.

For integer operands, division discards the fractional part toward zero. Converting the completed integer result to double cannot recover the discarded fraction. Convert an operand before division when a fractional result matters. Keep the small values below within range, and distinguish the stored value from how a stream chooses to display it.

#include <iostream>
int main() {
  const int items{17};
  const int boxes{4};
  std::cout << items / boxes << " "
            << static_cast<double>(items) / boxes << "\n";
}

4 4.25

The first division uses two integers. The cast changes one operand of the second division, so that calculation retains the fraction.