Programming Fundamentals · Lesson 10

C++ variables and data types

Declare and initialise variables, choose suitable types, and display a small learner profile.

Read the example

#include <iostream>
#include <string>

int main() {
    std::string learner{"Amina"};
    int lessonsCompleted{2};
    double studyHours{1.5};
    char group{'A'};
    bool readyToLearn{true};
    const int targetLessons{10};

    std::cout << "Learner: " << learner << '\n';
    std::cout << "Lessons: " << lessonsCompleted << '\n';
    std::cout << "Hours: " << studyHours << '\n';
    std::cout << "Group: " << group << '\n';
    std::cout << std::boolalpha << "Ready: " << readyToLearn << '\n';
    std::cout << "Target: " << targetLessons << '\n';
    return 0;
}

Learner: Amina
Lessons: 2
Hours: 1.5
Group: A
Ready: true
Target: 10

The braces initialise each variable. Use single quotes for the char 'A' and double quotes for the string "Amina". std::boolalpha displays a bool as true or false; the default numeric display would show 1 or 0.

Brace initialisation helps detect narrowing: int hours{1.5}; is rejected because the fraction would be lost. Use double hours{1.5}; instead. Floating-point numbers approximate many decimal fractions, so exact equality is not always appropriate.

Built-in types have limited ranges. Those ranges can vary by implementation; do not assume int is always the same size. The small whole numbers used in this lesson fit comfortably.

The const declaration prevents assigning a new value to targetLessons. Try changing lessonsCompleted after its declaration, then printing it again. Do not read an uninitialised local integer.

#include <iostream>
#include <string>

int main() {
    std::string learner{"Bilal"};
    int lessonsCompleted{3};
    double studyHours{2.5};
    char group{'B'};
    bool readyToLearn{false};

    std::cout << learner << '\n' << lessonsCompleted << '\n';
    std::cout << studyHours << '\n' << group << '\n';
    std::cout << std::boolalpha << readyToLearn << '\n';
    lessonsCompleted = 4;
    std::cout << "Updated lessons: " << lessonsCompleted << '\n';
    return 0;
}