Lab 1: Setup & C++

Github Classroom assignment

Introduction

Welcome to CS 1230!

The purpose of this lab is twofold: to set you up with what you'll need to work on assignments locally, and to ease you into C++, the programming language we'll be using in this course.

If you have any questions or run into any issues, please let us know over Ed or during TA hours. We'll do our best to help!

Objectives

1. Complete our Getting Started form,
2. Install Qt & Qt Creator locally on your computer,
3. Build and run a starter Qt program using the Qt Creator IDE, and
4. Learn about the basics (and subtleties) of C++.

Getting Started

We assume that you're already familiar with using Github Classroom to accept assignments, Ed to ask questions, and Gradescope to submit work. If you need a refresher on any of this, check out this page.

Please fill out our Getting Started form as you complete the steps below:

1. Read our course's collaboration policy,
2. Join the CS 1230 Ed discussion page (sign-up link),
3. Enroll in this course over on Gradescope using our entry code, K3387G,
4. Accept this lab's assignment from Github Classroom, and
5. Clone the resulting repository to your local machine.

At this point, you should have a copy of this lab's repository. All set? Let's get started!

Qt and Qt Creator

In CS 1230, we will be using Qt and Qt Creator to develop, build, and run all our projects and labs. Before we walk you through how to install them to your local machine, here's a brief description of each:

• Qt is a software used for building graphical user interfaces (GUIs) and cross-platform applications, e.g. for smart TVs or in-vehicle displays.
• Qt Creator is an integrated development environment (IDE) included with each Qt install. It provides useful tools for developing in C++, which you'll learn about later in the course.

We will be using Qt 6.2, which is a long-term support version. As for Qt Creator, any version is fine—it'd be easiest to just use the one that comes with your Qt install.

Installation

qtcreator

xcode-select -p

/Applications/Xcode.app/Contents/Developer

Instruction	Screenshot (click to expand)
Download and open the appropriate Qt installer for your operating system from the Qt installer page.
Follow the instructions on the installer to create a free Qt account (or use an existing one).
When prompted, opt for a Custom Installation.
On the next page, select (at least) these three: 1. Qt 6.2.4 > MinGW [...] (Windows) or Qt 6.2.4 > MacOS (MacOS), 2. Dev. and Designer Tools > CMake [...], and 3. Dev. and Designer Tools > Ninja [...]. Note 1: Qt Creator will be installed as well. You do not have to select it. Note 2: you may opt to install more components, but be warned that this will take up a lot more space on your machine!
Proceed with the installation. Once finished, launch Qt Creator.

Opening a Project

Instruction	Screenshot (click to expand)
In the Qt Creator application, click Open Project. In the file browser that appears, choose the CMakeLists.txt file located in your copy of this lab's repository.
You will then be asked to select a kit. If there are multiple options, select the one that has 6.2.4 in the title. Expand the details dropdown on the right and make sure that, at least, the Debug and Release options are selected.

After that, you should be taken to the Edit tab!

Using Qt Creator

Sidebar View

In the left sidebar, Qt Creator displays content based on the currently-selected 'sidebar view'. The two views you'll find mose useful are the Projects and File System views. Projects view shows a list of projects open in the current session, and the source, header, and other files for each; meanwhile, File System view shows all files in the currently selected directory.

We recommend using the Projects view most of the time! You can switch views by clicking on the dropdown menu at the top.

Project Settings

To modify the currently-selected project's settings, click 'Projects' on the left-most sidebar of your screen. These settings are divided into 'build' and 'run' settings.

In run settings, you can edit your command line arguments, which will be important for later assignments. For now, the most important setting you can edit here is your working directory.

For all assignments in CS 1230, you should always change your working directory to the parent folder of your project's CMakeLists.txt.

Extra: what is the significance of the working directory?

C++ is a compiled language, so an executable is produced at the end of the build process. The working directory is the directory from which this executable will be run.

Two important points follow:

1. This executable will be generated in a new build directory, which will be a "sibling" of your project's source directory. For example:

∟ build-lab01_setup_cpp_ghusername-<kit-name>-Release/ (build directory)
  ∟ lab01                                              (the executable)
∟ lab01-setup-cpp-ghusername/                          (source directory)
  ∟ CMakeLists.txt                                     (the file you opened in Qt Creator)
  ∟ src/
  ∟ resources/
    ∟ images/

2. By default, your project's working directory will be set to this build directory.

This is a problem because your application might try to access files using a file path relative to the source directory, but incorrectly looks for those files relative to the build directory.

Meanwhile, in build settings, you can select your build configuration from Debug, Release, and (possibly) others. A Debug build contains additional information internally that will be important if you're using the debugger, whereas a Release build is optimized to run faster.

We recommend using the Release configuration for all non-debugging work. Note that you can set the build configuration using a dropdown on the bottom left:

Running Your Project

Finally, you can run your project by hitting "Run"; this is the green play button in the above image. This will run your project in whatever build mode is currently selected.

You just ran a simple C++ program! Of course, it did nothing, but we can easily change that in the next section 🙂.

C++

Hello World

A simple C++ program that does nothing (like the one you just ran) looks something like this:

// A C++ program always starts from the main() function.
// main() returns an integer indicating how the program exited
int main() {
  // Though this function body is empty, it still returns an int!
  // In C++, if control reaches the end of main() without encountering
  // a return statement, the effect is that of executing `return 0;`
}

In order to modify this function to print "Hello world", we must first include the input/output library (iostream), which is a part of the C++ standard library.

#Include-ing Files

In C++ files, you can #include other files to gain access to functions, types, macros, and variables declared in those other files. For example, in our Hello World program, we can #include the iostream header file at the top of our main.cpp file like so:

#include <iostream> // Lines that begin with `#` do not require semi-colons

Note the use of angle brackets around iostream. In C++, you should use angle brackets for standard library files, but you should use double quotes for files within your own project.

Accessing Things in a Namespace

Imported functionality is usually grouped under a namespace, and we can access things within a namespace using the double-colon (::) operator. For example, since we included iostream in our Hello World program, we now have access to the following things in the std namespace:

• std::cout: prints things to stdout, i.e. the terminal or the "output" window in Qt Creator.
• std::endl: inserts a newline character and flushes the output stream.

std::cout is usually used in tandem with the insertion operator (<<). This inserts characters into the current output stream, and it works like string concatenation with + in some languages.

The insertion operator can also be used with std::endl to insert a newline, in place of \n.

Now, we can get into the fun stuff!

Primitive Types

C++ is a typed language. It comes with several primitive types, including...

• integer-like types (integers, booleans, characters)
• floating point types
• arrays (specifically, C-style arrays)
• functions and lambdas
• pointers and references

Some of these you might already know from languages you've learned before. Others, such as pointers and references, are C++ concepts that we'll expand on in later sections.

Note that strings are not a primitive type in C++, as string literals are simply char arrays. However, the standard library does provide the std::string type, which allows us to perform common string operations.

Variables

When defining a variable, we have to declare its type.

int x = 42;
double y = 3.14;

Alternatively, we may use auto to tell the compiler to deduce the variable's type, based on how we've initialized it. This could be useful if its type has a very long name, or if we're not sure about its exact type.

auto z = 2.71; // type of z deduced as double

// I'm not exactly sure about the type of this string literal
auto w = "random string abcd";

Functions

The same rules also apply to functions: we must declare their return types and the types of each parameter.

int plusOne(int x) {
  return x + 1;
}

Just as with variables, we may use auto in place of a specific return type—the compiler will deduce the return type from the return statement in the function body.

We may also use auto for trailing return type declarations (i.e. declaring the return type after the parameters, instead of before the function name). This could be useful for reducing visual clutter.

auto plusOne(double x) { // Using auto instead of a specific return type
  return x + 1;          // Return type deduced as double
}

// Trailing return type declaration (note the "->float")
// This is identical to "float plusOne(float x)"
auto plusOne(float x)->float {
  return x + 1;
}

Overloading

Defining multiple functions with the same names, but different type annotations, allows you to do something called overloading, which you might be familiar with from languages like Java.

int plusOne(int x) {
  return x + 1;
}

auto plusOne(double x) {
  return x + 1;
}

auto plusOne(float x)->float {
  return x + 1;
}

auto x = plusOne(42); // calls plusOne<int>
auto y = plusOne(3.14f); // calls plusOne<float>; note the float literal indicated by the letter "f"
auto z = plusOne(2.71);  // calls plusOne<double>

Generic Functions

We can improve the code in the example above by making our function generic. This is easy to do in C++: we simply change the type of its input parameter to auto.

auto plusOne(auto x) {
  return x + 1;
}

auto a = plusOne(1230); // a == 1231, instantiates plusOne<int>
auto b = plusOne(6.5f); // b == 7.5f, instantiates plusOne<float>
auto c = plusOne(3.14); // c == 4.14, instantiates plusOne<double>

Extra: Lambdas

There are also function-like entities in C++ called lambdas. We'll not explain them in detail since functional programming is outside the scope of this lab. However, you are welcome to play with them and ask questions about them on Ed.

You may need to use lambdas for certain extra credit features, such as multithreading, in your future assignments. To get you started, a toy example is shown below.

auto plus(auto increment) {
  return [=](auto x) {
    return x + increment;
  };
}

// Observe that functions are "first-class" in C++
auto apply(auto operation, auto x) {
  return operation(x);
}

auto x = apply(plus(20), 22); // x == 42
auto y = apply(plus(-1.1), 4.24); // y == 3.14

You can find more information about lambdas here.

A Warning About Type Deduction

You should be very careful to strike a balance between type declaration and type deduction to maximize your code clarity. We recommend only using auto for local variables in function bodies and for "generic" functions. Whenever possible, explicitly declare types in function signatures.

std::cout << timesTwo(123) << std::endl;
std::cout << timesTwo(3.14) << std::endl;
std::cout << timesTwo(std::string{ "abc" }) << std::endl;

Structs and Classes

Going beyond primitives, we can create custom types in C++ by combining existing types and bundling them with functions.

These custom types are known as structs/classes, and they can be defined using the struct/class keywords respectively.

Structs and classes are almost the same things in C++, with the only difference being that structs have public member access by default and classes have private member access by default. The basic form of a struct is shown as follows:

struct Rectangle {
  double length;    // A data member, also known as a field
  double width = 1; // Fields can have default values
  // Note: fields must be explicitly typed; you cannot use type deduction here

  // A member function, also known as a method
  double calculateArea() {
    return length * width;
  }

  // This member function modifies the struct instance's state
  void makeItASquare(double sideLength) {
    length = sideLength;
    width = sideLength;
  }
};

Here's how we can create instances of Rectangle:

// Create an instance of Rectangle
auto x = Rectangle{ .length = 2, .width = 4 };

// Field names can be omitted. Values in the brackets will
// be assigned to each field sequentially

// Equivalent to Rectangle{ .length = 4, .width = 3 }
auto y = Rectangle{ 4, 3 };

// Equivalent to Rectangle{ .length = 5, .width = 1 },
// because of the default value
auto z = Rectangle{ 5 };

And here's how we can use those instances:

// Remember that structs have public member access by default.
// If this Rectangle was a class, you'd have to declare the
// relevant fields/methods public to do this

// Getting and setting fields
auto oldLength = x.length;        // oldLength == 2
x.length = 4;

// Calling member functions
auto newArea = x.calculateArea(); // newArea == 16
x.makeItASquare(oldLength);       // x.length == x.width == 2

Now, we have 2 types Rectangle and Circle, with the same member functions calculateArea and calculatePerimeter. Can we define one printShape function that works for both types?

Generic Functions (Reprise)

If you have previous experience in OOP, you might think of defining a Shape interface with a printShape() abstract function, and have both Rectangle and Circle both implement Shape. This is unnecessary in C++.

Remember the generic functions we learned in the previous section? If a function has a parameter of auto type, it is allowed to be anything! We can pass Rectangle and Circle instances to it just like that!

// a function template that only accepts containers with no more than 42 elements
// simulating a dependently typed function
auto f(auto x) requires (x.size() <= 42) {
    // empty
}

f(std::array<int, 10>{}); // OK
// f(std::array<int, 43>{}); <- error

// a function template whose return type depends on its input
// simulating an untyped function
auto g(auto x) {
    // if the input can be invoked like a function
    // the return type is the same as the input's return type
    if constexpr (requires { x(); })
        return x();
    // otherwise return type is int
    else
        return 42;
}

auto x = g([] { return 2.71; }); // x is of type double
auto y = g("aaa"); // y is of type int

void printShape(auto shape) {
  // Your code here
}

Area: /* area of the shape */
Perimeter: /* perimeter of the shape */

Other Standard Library Utilities

Besides iostream, the C++ standard library provides us with many useful utilities, and we'll focus on the four most commonly used ones: its containers and strings.

Arrays

std::array is a fixed-length array.

#include <array>

auto x = std::array<int, 3>{}; // Must declare element type and length

// Element type and length can be deduced if you immediately initialize
// the array with values
auto y = std::array{ 3.14f, 2.71f };

// Getting and setting array elements
auto z = y[0]; // z == 3.14f
x[0] = 42; // now, the zeroth element of x is 42

auto [a, b, c] = x; // Arrays can be unpacked: a == 42, b == 0, c == 0

// Commonly used array methods
auto lengthX = x.size();
auto underlyingPointer = x.data(); // we'll explain pointers later

// Arrays can be looped over element-wise
for (auto element : y) {
  std::cout << element << std::endl; // prints 3.14, then 2.71
}

Vectors

std::vector is a dynamic-length array. Unlike std::array, it allows us to insert or remove elements at any time, and it has mostly the same capabilities as std::array. However, std::array is slightly more performant as it doesn't require dynamic memory allocation.

#include <vector>

auto x = std::vector<int>{}; // Must declare element type

// Element type can be deduced if you immediately initialize
// the vector with values
auto y = std::vector{ 3.14f, 2.71f };

// Manipulating vector elements
auto z = y[0]; // z == 3.14f
x.push_back(42); // add an element to the end of the vector
x.push_back(123); // add another element after the 42 we just inserted
x.pop_back(); // remove the element we just added

// Commonly used vector methods
auto lengthX = x.size();
y.reserve(20); // Pre-allocate memory for more elements. Its length stays the same
x.resize(10); // Resize the vector, actually changing its number of elements (length)
auto underlyingPointer = x.data(); // we'll explain pointers later

// Vectors can be looped over element-wise
for (auto element : y) {
  std::cout << element << " "; // prints 3.14, then 2.71
}

Tuples

std::tuple is a heterogeneous container—it is capable of storing elements of different types. It is most commonly used to achieve multiple return values in C++.

#include <tuple>

auto makeTuple(auto x, auto y) {
  return std::tuple{ x, y };
}

auto [x, y] = makeTuple(42, 3.14); // tuples can be unpacked, x == 42, y == 3.14

// This is a variadic function template: it takes any number of arguments, each of any type
// It is unlikely that you'll need to use variadic functions for this course
auto doubleEach(auto ...x) {
  return std::tuple{ x + x... };
}

auto [a, b, c] = doubleEach(12, 2.71, std::string{ "abc" });
// a == 24, b == 5.42, c == "abcabc"

Strings

std::string provides basic string operations in C++. You can find its documentation here.

#include <string>

auto x = std::string{}; // Create an empty string
auto y = std::string{ "hello!" }; // Convert a string literal to a std::string

using namespace std::literals; // Use this namespace to create std::string literals
auto z = "abcd"s;              // Create a std::string literal, note the s suffix
z += "efgh";                   // Use + to concatenate strings

Iterating Over Containers

Defining containers is one thing, but we also need to know how to operate over the elements. There are two primary methods for iterating: the range-for loop, and index-based iteration.

// range-for
for (auto element : container) {
  // use element
}

// index-based
for (auto index = 0; index < container.size(); ++index) {
  auto element = container[index];
  // use element
}

Note that a more efficient way of doing the range-for loop is to use an ampersand after auto. You will learn more about what this means in the section on references.

// reference based range-for
for (auto& element : container) {
  // use element by reference
}

Pointers and References

Every entity in our program, from variables to functions to constants etc, all exist somewhere in memory, and they all have a unique memory location called a memory address.

A pointer is an integer storing a memory address, and it allows us to manipulate the object at that address. We can obtain a pointer to almost anything in C++ by taking its address using the address of operator &. The obtained address will be of a pointer type, denoted by the target object type followed by an asterisk *.

int x = 42;
int* px = &x; // px is a pointer to an integer, pointing to x
auto px2 = &x; // type deduction works for pointers too, type of px2 deduced to int*
auto* px3 = &x; // partial type deduction works too, px3 is a pointer to some deduced type, auto deduced to int
// pointer variables themselves also reside somewhere in memory, you can get a pointer to pointer
auto ppx = &px; // ppx is of type int**, a pointer to a pointer to an integer
// let's see where x is located in (virtual) memory!
auto MemoryAddressOfX = reinterpret_cast<unsigned long long>(px); // cast pointer to largest integer type
std::cout << MemoryAddressOfX;

The first thing we can do with a pointer is to access the entity at the address that the pointer points to. This can be achieved by using the dereference operator which also has the form of a star *. For pointers to non-primitive types, we can also use -> to access its members.

auto x = 42;
auto y = Rectangle{ .length = 4, .width = 2 };
auto px = &x;
auto* py = &y; // you could still write out * along with auto to make it extra clear that it is a pointer.

// This is how we access the object that a pointer points to
auto x2 = *px; // x2 == x == 42
auto y2 = *py; // y2 == y == Rectangle{ .length = 4, .width = 2 }
auto a = py->calculateArea(); // same as y.calculateArea()
auto yLength = py->length; // same as y.length

Dereferencing a pointer also allows us to modify the object that it points to

auto x = 42;
auto y = Rectangle{ .length = 4, .width = 2 };
auto px = &x;
auto py = &y;

*px = 123; // this sets x to 123
py->width = 3; // this sets y.width to 3

std::cout << x; // you should see 123 here
std::cout << y.width; // you should see 3 here

void inplaceTimesTwo(/* ??? pointerToSomeVariable */) {
    // your code here
}

auto x = 21;
auto y = std::string{ "abcd" };

inplaceTimesTwo(&x);
inplaceTimesTwo(&y);

std::cout << x; // you should see 42 here
std::cout << y; // you should see "abcdabcd" here

You might've noticed that pointers are somewhat unwieldy to use; we have to first take the address of something, then dereference the pointer. This can be simplified by the use of references. A reference is essentially a dereferenced pointer, meaning the entity at a particular memory address. You can find more information about the connection between pointers and references here. The reference type is denoted by the entity type followed by &.

int x = 42;
int& refx = x; // a reference to x, it has the same memory address as x
auto& refx2 = x; // we may use type deduction with references, type of refx2 deduced to int&

refx = 123; // this sets x to 123 because refx and x share the same memory address
std::cout << x; // you should see 123 here

One thing we have to be careful about with references is that we always have to spell out & in the type declaration when creating a reference, whether we're using type deduction or not. Otherwise, we'd be creating a copy rather than a reference.

int x = 42;

int& refx = x; // a reference to x, same memory address as x
auto& refx2 = x; // a reference to x, same memory address as x

int y = x; // this is a copy of x! it's a new variable with its own unique address!
auto y2 = x; // again, it's a copy with its own unique address!

This is because C++ has value semantics by default.

Now that we know C++ makes a copy when creating something from another unless specified otherwise (i.e. creating a reference). We should really change most of the parameter types in our function signature to references unless it's something trivial like an int or double. Otherwise, a full copy will be made for every object we passed to the function, and it could lead to serious performance problems!

void func(std::vector<int> things) {
    // empty
}

void betterFunc(std::vector<int>& things) {
    // empty
}

auto things = std::vector{ 1, 2, 3, 4 };

func(things); // 'things' will be shallow-copied when you call func(), because it gets passed by value!

betterFunc(things); // no copy will be made here! because 'things' gets passed by reference!
// This also means if betterFunc modifies 'things' in any way in its function body, it will be reflected here

The same also applies to looping over containers. You need to use references in a range-for loop to modify elements.

auto things = std::vector{ 1, 2, 3, 4 };
// this copies every element in 'things'
// not ideal if the element type is not trivial to copy
for (auto x : things) {
    std::cout << x << std::endl;
}

for (auto& x : things) { // this loops over each element by reference
    x += x;              // which also enables you to modify the elements
}

// now things = [2, 4, 6, 8]

void doubleEachElement(/* ??? container */) {
    // your code here
}

End

Congrats on finishing the Setup & C++ lab! Now, it's time to submit your code and get checked off by a TA. If you wish to have a deeper understanding of C++ or learn advanced C++ features to better your program design, you can find more information in our advanced C++ tutorial coming soon!

Submission

Submit your Github repo for this lab to the "Lab 1: Setup & C++" assignment on Gradescope, then get checked off by a TA during lab hours.

Please let us know if you find any mistakes, inconsistencies, or confusing language in this or any other CS 1230 document by filling out our anonymous feedback form.