Data Types

Constants

Constants name values that should not change after they are initialized.

const Use `const` for a value that should stay fixed.

Constants

hours
constants.cpp
Replay: real traced execution (multi-file project)
#include <iostream>

int main() {
    const int minutesPerHour = 60;
    int hours = 2;
    int totalMinutes = hours * minutesPerHour;

    std::cout << "hours=" << hours << std::endl;
    std::cout << "minutes=" << totalMinutes << std::endl;
    return 0;
}

#include <iostream>

int main() {
    const int minutesPerHour = 60;
    int hours = 1;
    int totalMinutes = hours * minutesPerHour;

    std::cout << "hours=" << hours << std::endl;
    std::cout << "minutes=" << totalMinutes << std::endl;
    return 0;
}

#include <iostream>

int main() {
    const int minutesPerHour = 60;
    int hours = 4;
    int totalMinutes = hours * minutesPerHour;

    std::cout << "hours=" << hours << std::endl;
    std::cout << "minutes=" << totalMinutes << std::endl;
    return 0;
}

  1. minutesPerHour ← 60, hours ← 2, totalMinutes ← 120

    3int main() {4    const int minutesPerHour→ 60 = 60;5    int hours→ 2 = 2; //@hours=1, 46    int totalMinutes→ 120 = hours2 * minutesPerHour60;78    std::cout << "hours=" << hours2 << std::endl;9    std::cout << "minutes=" << totalMinutes120 << std::endl;10    return 0;11}
    outputhours=2
minutes=120

  1. minutesPerHour ← 60, hours ← 1, totalMinutes ← 60

    3int main() {4    const int minutesPerHour→ 60 = 60;5    int hours→ 1 = 1;6    int totalMinutes→ 60 = hours1 * minutesPerHour60;78    std::cout << "hours=" << hours1 << std::endl;9    std::cout << "minutes=" << totalMinutes60 << std::endl;10    return 0;11}
    outputhours=1
minutes=60

  1. minutesPerHour ← 60, hours ← 4, totalMinutes ← 240

    3int main() {4    const int minutesPerHour→ 60 = 60;5    int hours→ 4 = 4;6    int totalMinutes→ 240 = hours4 * minutesPerHour60;78    std::cout << "hours=" << hours4 << std::endl;9    std::cout << "minutes=" << totalMinutes240 << std::endl;10    return 0;11}
    outputhours=4
minutes=240

Follow the Constant

  1. hours starts at 2.
  2. minutesPerHour is the constant 60.
  3. minutes = hours * minutesPerHour.
  4. The default calculation is 2 * 60.
  5. The program prints hours=2 and minutes=120. | hours | minutesPerHour | minutes | | --- | --- | --- | | 1 | 60 | 60 | | 2 | 60 | 120 | | 4 | 60 | 240 |

Exercise: constants.cpp

Reproduce minutes=120, then use hours 1 and 4 to predict each minutes value.