Intro to C++

Computer Graphics and Imaging

UC Berkeley CS 184/284A

Discussion 1

Why C++?

• Graphics is computation-heavy → want to optimize for efficiency.
• e.g. a 1000x1000 px image needs to run some operation 1,000,000 times.
• C++ is must faster than other languages, such as Java and Python.
• C++ offers finer control of computer resources.
• C++ is object-oriented.
• C++ is statically typed.
• Have to build C++ code before running it.
• Used frequently in games & animation software.

C++ in CS 184/284A

• Homeworks are primarily in C++.
• We do not require expertise on the details of C++.
• Exams test for understanding of graphics concepts, not C++ syntax.

What does this code do?

#include <iostream>

using namespace std;

int main()

{

cout << "Enter a positive integer: ";

int n;

cin >> n;

​

int k = 1;

for (int i = 1; i <= n; i++) {

k *= i;

}

​

cout << "The number " << n << " turns into " << k << endl;

return 0;

}

What does this code do?

#include <iostream>

using namespace std;

int main()

{

cout << "Enter a positive integer: ";

int n;

cin >> n;

​

int k = 1;

for (int i = 1; i <= n; i++) {

k *= i;

}

​

cout << "The number " << n << " turns into " << k << endl;

return 0;

}

• Syntax is very similar to Java.
• #include <iostream> is a library import.
• Must declare type when initializing variables.

Namespaces, Classes, and Objects

Namespaces

• I create “x”, and you create “x”. Later on, a code asks for “x”, but which one does it use?
• To solve this: C++ has namespaces.
• Namespaces provide additional scope for variables, functions, and classes.

​

• For example:
• Two different classes called Base.
• If they are in different namespaces (A vs. B), they won’t conflict with each other.
• The code tells them apart by specifying A::Base and B::Base.

Namespaces Example

#include <iostream>

​

namespace hello {

int x = 5; // variable inside namespace

}

​

int main() {

int x = 123; // local variable

std::cout << x << std::endl; // prints “123”

std::cout << hello::x << std::endl;

// prints “5”

}

We can declare two x variables! One inside the namespace and one outside.

​

To refer to a namespace variable:

hello::variable

Namespaces Example

​

#include <iostream>

​

namespace n {

int x = 5;

}

namespace n2 {

int x = 4;

}

​

using namespace n;

​

​

int main() {

std::cout << x << std::endl; // Prints 5

}

Alternatively, use the using keyword.

​

Namespaces Example

​

#include <iostream>

​

namespace n {

int x = 5;

}

namespace n2 {

int x = 4;

}

​

using namespace n;

using namespace n2;

​

int main() {

std::cout << x << std::endl; // which x is it????

}

Alternatively, use the using keyword.

Careful: It could cause ambiguities if you’re using multiple namespaces with the same variable names.

​

Similar bad practice in Python:

from module_1 import *�from module_2 import *

Namespaces Example

​

#include <iostream>

​

namespace n {

int x = 5;

}

namespace n2 {

int x = 4;

}

​

using namespace n;

using namespace n2;

​

int main() {

std::cout << x << std::endl; // which x is it????

}

The compiler will tell you something’s wrong!

Classes & Objects

• All the usual OOP concepts exist in C++:
• Objects, classes, abstraction, inheritance, polymorphism, etc.
• Just with slightly new syntax!
• All methods & attributes of a C++ class are private, unless explicitly declared public.
• C++ also has structs → like classes, but all visibilities public by default.

struct Student {

std::string student_name;

int age;

bool enrolled_in_cs184;

};

Classes and Objects

#include <iostream>

​

class Rectangle {

private:

int width;

int height; // private variables

public:

void set_values (int,int);

int area();

// functions to declare

};

void Rectangle::set_values(int x, int y) {

width = x;

height = y;

}

int Rectangle::area() {

return width * height;

}

int main() {

Rectangle rect;

rect.set_values (3,4);

std::cout << "Area: " << rect.area();

return 0;

}

// What is the output?

Classes and Objects

#include <iostream>

​

class Rectangle {

private:

int width;

int height; // private variables

public:

void set_values (int,int);

int area();

// functions to declare

};

void Rectangle::set_values(int x, int y) {

width = x;

height = y;

}

int Rectangle::area() {

return width * height;

}

int main() {

Rectangle rect;

rect.set_values (3,4);

std::cout << "Area: " << rect.area();

return 0;

}

// What is the output?

12

Header Files

• You might see a .cpp and .h file with the same name in your assignments:
• .cpp contains what is actually compiled and run.
• Code, logic, algorithms, instructions.
• e.g. function bodies.
• .h is a “header” file meant to be imported.
• Class definitions, data structures, interfaces.
• e.g. function declarations.
• They are like a “table of contents”.
• Many .cpp files can #import the same .h file!

.cpp vs. .h

// Rectangle.h:

​

class Rectangle {

private:

int width;

int height;

public:

void set_values(int,int);

int area();

};

// Rectangle.cpp:

​

#include “Rectangle.h”

void Rectangle::set_values(int x, int y) {

width = x;

height = y;

}

int Rectangle::area() {

return width * height;

}

​

// We write out the explicit code for the method in the .cpp file!

.cpp vs. .h

// Rectangle.h:

​

class Rectangle {

private:

int width;

int height;

public:

void set_values(int,int);

int area();

};

// main.cpp:

​

#include “Rectangle.h”

​

int main() {

Rectangle rect;

rect.set_values (3,4);

std::cout << "Area: " << rect.area();

return 0;

}

Memory Allocation

Different from Java but very similar to C!

Pointers and Addresses

• A variable in C++ is assigned an address in computer memory.
• That’s where the variable’s value is stored!

​

​

Pointers and Addresses

• A variable in C++ is assigned an address in computer memory.
• That’s where the variable’s value is stored!

​

• A pointer is a variable whose value is the address of another variable.

Pointers and Addresses

• It must have a type.
• Initialized using an asterisk *

​

int *x;

// pointer variable is named x

// stores the address of an int in memory

Reference & Dereference Operators

• Reference operator (&) → gives the address occupied by a variable.

​

Reference & Dereference Operators

• Reference operator (&) → gives the address occupied by a variable.
• Dereference operator (*) → gives value stored at a memory address.

Pointers Example

// Example program

#include <iostream>

#include <string>

​

int main()

{

int *a;

int x = 3;

a = &x;

std::cout << a << std::endl;

std::cout << *a << std::endl;

*a = 100;

std::cout << *a << std::endl;

std::cout << x << std::endl;

}

Pointers Example

// Example program

#include <iostream>

#include <string>

​

int main()

{

int *a;

int x = 3;

a = &x;

std::cout << a << std::endl;

std::cout << *a << std::endl;

*a = 100;

std::cout << *a << std::endl;

std::cout << x << std::endl;

}

1. Initialize a pointer named a.
2. Initialize a variable named x and set it to 3.

​

Pointers Example

// Example program

#include <iostream>

#include <string>

​

int main()

{

int *a;

int x = 3;

a = &x;

std::cout << a << std::endl;

std::cout << *a << std::endl;

*a = 100;

std::cout << *a << std::endl;

std::cout << x << std::endl;

}

1. Initialize a pointer named a.
2. Initialize a variable named x and set it to 3.
3. Set a to the address of x.

Pointers Example

// Example program

#include <iostream>

#include <string>

​

int main()

{

int *a;

int x = 3;

a = &x;

std::cout << a << std::endl;

std::cout << *a << std::endl;

*a = 100;

std::cout << *a << std::endl;

std::cout << x << std::endl;

}

1. Initialize a pointer named a.
2. Initialize a variable named x and set it to 3.
3. Set a to the address of x.
4. Print a's value (this is an address!).
5. Print the value at the address that a is storing.

​

Pointers Example

// Example program

#include <iostream>

#include <string>

​

int main()

{

int *a;

int x = 3;

a = &x;

std::cout << a << std::endl;

std::cout << *a << std::endl;

*a = 100;

std::cout << *a << std::endl;

std::cout << x << std::endl;

}

1. Initialize a pointer named a.
2. Initialize a variable named x and set it to 3.
3. Set a to the address of x.
4. Print a's value (this is an address!).
5. Print the value at the address that a is storing.
6. Reassign the value at the address that a is storing to be 100.

Pointers Example

// Example program

#include <iostream>

#include <string>

​

int main()

{

int *a;

int x = 3;

a = &x;

std::cout << a << std::endl;

std::cout << *a << std::endl;

*a = 100;

std::cout << *a << std::endl;

std::cout << x << std::endl;

}

1. Initialize a pointer named a.
2. Initialize a variable named x and set it to 3.
3. Set a to the address of x.
4. Print a's value (this is an address!).
5. Print the value at the address that a is storing.
6. Reassign the value at the address that a is storing to be 100.
7. Print the value at the address that a is storing.
8. Print the value of x (which has now changed!).

-> Operator

Rectangle *x = new Rectangle(3, 4);

int w = x->width;

// this is the same as (*x).width

Rectangle x = Rectangle(3, 4);

int w = x.width;

x.area();

-> Operator

Rectangle *x = new Rectangle(3, 4);

int w = x->width;

// this is the same as (*x).width

x->area();

// also used to call methods

Rectangle x = Rectangle(3, 4);

int w = x.width;

x.area();

Memory Management

• Memory in your program can be allocated on the stack or the heap:

​

Memory Management

• Memory in your program can be allocated on the stack or the heap:
• Stack → allocation and deallocation is automatically done.

​

Memory Management

• Memory in your program can be allocated on the stack or the heap:
• Stack → allocation and deallocation is automatically done.
• Heap → needs to be done by the programmer manually.

​

Memory Management

• Memory in your program can be allocated on the stack or the heap:
• Stack → allocation and deallocation is automatically done.
• Heap → needs to be done by the programmer manually.

​

• The new operator requests memory allocation on the Heap.
• Like malloc in C. (C++ has malloc but it’s less user-friendly.)

Stack

Rectangle rect;

OR

Rectangle rect = Rectangle();

​

• No need to delete
• To get attributes/methods, use . (rect.width)
• If constructor has arguments:

​

Rectangle rect(3, 4);

OR

Rectangle rect = Rectangle(3, 4);

Rectangle *rp = new Rectangle();

​

• Later, must call delete rp; or it will exist until your program ends.
• To get attributes/methods, use -> (rp->width)
• If constructor has arguments:

​

Rectangle *rp = new Rectangle(3, 4);

Heap

Passing Arguments

Pass By Value

int square_value(int a) {

return a * a;

}

​

int main() {

int x = 2;

x = square_value(x);

}

Pass By Value

int square_value(int a) {

return a * a;

}

​

int main() {

int x = 2;

x = square_value(x); // x is now 4!

}

Pass By Pointer

void square_pointer(int *a) {

*a = (*a) * (*a);

}

​

int main() {

int x = 2;

// Passing in an address

square_pointer(&x);

}

Pass By Pointer

void square_pointer(int *a) {

*a = (*a) * (*a);

}

​

int main() {

int x = 2;

// Passing in an address

square_pointer(&x); // After this line, x = 4

}

Pass By Reference

void square_reference(int &a) {

a = a * a;

}

​

int main() {

int x = 2;

square_reference(x); // After this line, x = 4

}

Pass By Pointer vs. Reference vs. Value

void square_pointer(int *a) {

*a = (*a) * (*a);

}

​

void square_reference(int &a) {

a = a * a;

}

​

int square_value(int a) {

return a * a;

}

​

int main() {

int x = 2;

square_pointer(&x); // After this line, x = 4

square_reference(x); // After this line, x = 16

x = square_value(x); // After this line, x = 256

}

Common Built-in Data Structure: vector!

Vectors

• std::vector is something you’ll use a lot in projects!
• It’s an ordered list of items, similar to:
• Java ArrayList
• Python List

Vectors Example

int main() {

// We initialize a vector with an initializer list

std::vector<int> nums = {2, 4, 6, 0, 1};

​

// Access by index

std::cout << "nums[2] is " << nums[2] << std::endl;

​

// Index-based iteration

for (int i = 0; i < nums.size(); i++) {

std::cout << nums[i] << " "; // prints 2 4 6 0 1

}

​

// Range for loop

for (int x : nums) {

std::cout << x << " "; // prints 2 4 6 0 1

}

}

Range For Loops Warning

int main() {

// We initialize a vector with an initializer list

std::vector<Image> images = std::vector<Image>(5);

​

// Range for loop (items are copied here)

for (Image image : images) {

//do something

}

}

Range For Loops Warning

int main() {

// We initialize a vector with an initializer list

std::vector<Image> images = std::vector<Image>(5);

​

// Range for loop (over references)

for (Image &image : images) {

//do something

}

​

// Alternatively:

for (auto it = images.begin(); it != images.end(); ++it) {

//do something

}

}

Additional Resources

• C++ Intro from Spring 2024
• And a more detailed guide linked from that doc
• Ask ChatGPT to translate C++ code into your language of choice.
• Just remember to review our policy on AI tools!!!
• You can also learn a lot just by poking around existing code in your assignments!

Thanks for coming!