Introduction
What is C++?
Put simply, C++ is a compiled language that is statically typed. This brings about two obvious questions:
What does it mean to be a compiled language?
What does it mean to be statically typed (and what is a type)?
A compiled language is one where we need to pass our written code to a piece of system software called a compiler (more accurately, a compiler driver) that will translate our high-level program into instructions that the machine can understand. For example, we can pass a high-level program written in C++ to a compiler driver like g++ to translate it into an executable (something we can execute).
A type describes a value in our program. This includes information about its size, and what operations we can be performed with that value. There are built-in types like float and int in C++ that describes fractional and whole numbers respectively. There are also more complex types and data structures that are part of the C++ Standard Library, like the hash table std::unordered_map. We can additionally define our own types through the struct and class keywords.
A statically-typed language is one where every value in our program has a single type than can not be changed, and that type is known at compile time. For example, when we define a variable in our program, we must give it a type (or the compiler must be able to infer the type). The same is true for function return values and parameters.
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What Is Modern C++?
The C++ language has evolved significantly since its creation (especially in the past 10-15 years). When we talk about writing “modern C++”, we typically mean writing C++ using features and syntax from the latest published standards.
For some, this means writing C++11 code. For others, this can mean using features from C++23. The exact answer to this question depends on who you’re talking to, and the project you’re working on.
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The Core of C++ Applications
C++ programs are centered around functions.
A function is how we tie a logical name to a sequence of statements. They have 4 key parts:
A name
We use this identifier to execute/call our function
A list of 0 or more parameters
A list of inputs to our function
A return type
The type of the output value
A function body
The sequence of statements to run when we execute/call our function
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Where Do Programs Begin?
The core of every C++ application is a function named main. The main function is special for a few reasons:
It is the logical starting point of execution of every C++ program
It must be included in every C++ program
It is not a function we directly call
It is called automatically when we execute our applications
It only has 2 valid forms to choose from
The most simple program we can write in C++ is simply a main function that does (essentially) nothing:
Here, we used the form of main without input parameters. This form includes:
A name
main
A list of parameters (empty)
()
A return type
int
A function body
The single
return 0;statement encased in{}
The return type of main is special, as it indicates the success of execution for our program. A return value of 0 means the program completed without error. Non-zero return values from main are error codes (to help explain why execution failed).
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How Do Turn Off Our Code?
Comments are pieces of text in our code that are completely ignored by our compiler. We use comments for a number of things, including:
Annotating what our code is doing
Disabling pieces of code, but not deleting them
In C++, we have two forms of comments:
Single line comments
All text following
//on a single line
Block comments
All text contained within
/*and*/
