C++ Basics — Praneeth Suresh

Program Execution Model

C++, like C, is compiled ahead of time to native machine code. Each source file (a translation unit) is preprocessed and compiled into an object file; the linker then combines the object files with libraries into one executable. Java is different: javac produces bytecode, which the JVM loads, verifies, and may JIT-compile while the program runs.

With GCC, use the g++ driver to compile and link C++ in one step:

bash

g++ hello-world.cpp -o hello-world

g++ compiles .cpp, .cc, and .cxx files as C++ and, in the link step, adds the C++ standard library (libstdc++). Running gcc on a .cpp file also compiles it as C++, but gcc does not link libstdc++ by default, which is why that command often fails at link time with undefined std:: symbols.

Basic Syntax

Most of this is similar to C, with headers that can be used to include packages and a main() function that is the core of the execution.

Basic I/O

Here is a basic example of outputting a string:

c++

std::cout << "Hello World"

The above line prints the text to the console.

You can remember << as pushing the text into the output stream (i.e std::cout in this case)

To add a newline, we can add the following to the end of the string:

c++

std::cout << "Hello World" << std::endl;

In fact, this is a general idea of how we can build streams using << where we can chain the operator to add multiple objects to the stream.

Now, for inputs, we can use std::cin >>. Here is an example of how this fits into a program.

c++

#include <iostream>

int main() {
    int x;
    std::cin >> x;
    std::cout << "You entered: " << x << std::endl;
}

Note that the direction of the arrows (>>) for std::cin is now reversed compared to <<. You can remember as data flowing into x.

If you find prefixing std:: before the function calls cumbersome, you can omit it with using namespace std. Here is an example:

c++

#include <iostream>
using namespace std;
int main() {
    int x;
    cin >> x;
    cout << "You entered: " << x << endl;
}

However, this is generally discouraged in larger projects as it does lead to naming conflicts.

Variables

There are some universal programming language ideas here, which overlap with C. However, while both languages use variables as named memory locations to store data, C++ introduces significant new types and rules for how and where variables can be used.

Here are some differences to keep in mind:

Reference Variables: C++ introduces references (type&), which act as aliases for existing variables. C does not have references and must use pointers (type*) for similar functionality.
Declaration Placement: In older versions of C, local variables usually had to be declared at the very start of a block (before any statements). C++ (and modern C99+) allows variables to be declared anywhere in the code, typically right before they are first used.

The rest of the basic ideas about variables such as initialization, declaration, arithmetic operations and data types are the same as C.

Statements

The statements and operations in C++ are a super-set of what is available in C. C++ extends the set significantly with new operators, exception handling, and overloading.

New Operators in C++:

Scope resolution (::) – lets you access global variables or class members.
Member access (>*, .*) – for pointers to members.
Dynamic memory (new, delete) – replaces malloc/free in idiomatic C++.
Type casting operators – static_cast, dynamic_cast, const_cast, reinterpret_cast (more controlled than C’s (type) cast).
Overloading – operators can be redefined for user-defined types in C++.

New Statements in C++:

C++ adds try/catch/throw for exception handling, which C does not have.
C++ also allows range-based for loops (since C++11), which don’t exist in C.
C++ supports new control statements like using for namespaces and type aliases, absent in C.

Increment/Decrement Nuance:

Both languages have ++ and -, but in C++ these can be overloaded for custom classes, while in C they only apply to built-in numeric types.