C++ fundamentals · Lesson 2 of 21

Variables and types

int, double, char, bool, string, auto and const, and why types matter.

9 minutes3 games

In C++ you state each variable's type when you declare it, and it never changes. That's static typing: the compiler knows everything before the program runs, catches many mistakes early, and reserves exactly the right amount of memory.

C++

#include <iostream>
#include <string>

int main() {
    int age = 20;
    double gpa = 3.75;
    char grade = 'A';
    bool enrolled = true;
    std::string name = "Laila";
    const int maxCourses = 5;
    auto score = 98.5;          // the compiler works out: double

    std::cout << name << " is " << age << ", grade " << grade << "\n";
    std::cout << "GPA " << gpa << ", enrolled: " << enrolled << "\n";
    std::cout << "max " << maxCourses << ", score " << score << "\n";
    return 0;
}

age20int · 4 bytes

gpa3.75double · 8 bytes

grade'A'char · 1 byte

enrolledtruebool · 1 byte

name"Laila"std::string

Each type takes a known amount of space. (These are the usual sizes; the standard only sets minimums.)

Notice bool printed 1, not true. A char uses single quotes 'A', a string double quotes "Laila". const means the value never changes; try to change it and the compiler refuses.

The division and overflow traps

C++

#include <iostream>
#include <climits>

int main() {
    std::cout << 7 / 2 << "\n";        // int / int  -> int
    std::cout << 7 / 2.0 << "\n";      // one double -> double

    int big = INT_MAX;
    std::cout << big << "\n";
    long long bigger = static_cast<long long>(big) + 1;
    std::cout << bigger << "\n";
    return 0;
}

What's the output?

#include <iostream>
int main() {
    int a = 9, b = 4;
    double c = a / b;
    std::cout << c << "\n";
}

What will this code print?

Complete the code

Complete it so the division gives 2.25.

#include <iostream>
int main() {
    int a = 9, b = 4;
    double c = <double>(a) / b;
    std::cout << c << "\n";
}

Exercise

You have int total = 17 and int count = 4. Print the average with its fraction (4.25).

Expected output: 4.25

C++

#include <iostream>

int main() {
    int total = 17;
    int count = 4;
    std::cout << total / count << "\n";
    return 0;
}

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#include <iostream> #include <string> int main() { int age = 20; double gpa = 3.75; char grade = 'A'; bool enrolled = true; std::string name = "Laila"; const int maxCourses = 5; auto score = 98.5; // the compiler works out: double std::cout << name << " is " << age << ", grade " << grade << "\n"; std::cout << "GPA " << gpa << ", enrolled: " << enrolled << "\n"; std::cout << "max " << maxCourses << ", score " << score << "\n"; return 0; }