Getting Started
There are some basic things you need to know to start coding C++ applications. These foundational topics include C++ expressions and statements, comments in C++ source code, and the difference between .cpp
and .h
files.
Table of Contents
- Expressions and Statements
- Expressions
- Statements
- Of Semicolons and Mustache Braces
- Comments
- Files Types
- Further Reading
Expressions and Statements
The building blocks of C++ applications are the commands we give the computer in our code. We call these commands statements. The body of any function is a sequence of statements.
One type of statement is an expression statement. Expressions are the parts of our code the computer can simplify to a final value with a data type.
Expressions
The most basic expressions are literal values like 10
or 4.2
or "Wally"
.
Literals combined with operators also make expressions. 10 * 2
and true || false
are expressions that evaluate to 20
and true
respectively.
Variables can be used in expressions too, like length
or length * width
or width + length + 22
. Variables must be defined before use.
Assignments and function calls are also considered to be expressions: int area = length * width
or someFunction(5)
or even someFunction(length * width)
.
Statements
Expression statements are just one type of statement. There are also:
- Compound Statements - Collection of statements grouped by curly braces
{}
. Often called blocks. - Selection Statements - Flow control like
if/else
andswitch
. Also called decision statements. - Iteration Statements - Repetition control for blocks of statements like
while
orfor
. - Jump Statements - Unconditional changes to a program’s execution flow like
return
orbreak
. - Declaration Statements - Define variables, functions, namespaces, templates, and more.
- Try Blocks - Error-handling mechanism for catching exceptional circumstances.
Of Semicolons and Mustache Braces
Some types of expressions must be terminated by a semi-colon to be considered valid:
- Expression Statements. Example:
helloWorld("Wally");
- Jump Statements. Example:
return 0;
- Declaration Statements. Example:
int answer = 32;
Other statements are best made using curly braces:
- Compound Statements
- Selection Statements
- Try Blocks
Here’s an example of a selection statement using curly braces:
if (answer == 42) {
helloWorld("Wally");
return;
} // No trailing semicolon after the close brace.
Comments
C++ uses C-style single-line and multi-line comments:
// Single line comments start with two forward slashes.
helloWorld("Daisy"); // Comments can be placed on the same line as source code.
/*
Multi-line comments start with a forward-slash followed by an asterisk,
and continue until they are terminated by an asterisk followed by a forward-slash.
*/
/* Multiline syntax can also be used on a single line. */
Comments are replaced by blank space during the compilation process.
Files Types
We use two types of files when writing a C++ application:
- Header Files - Home to function and class definitions. Saved with a
.h
or a.hpp
file extension. - C++ Source Files - Home to function and class implementations. Saved with a
.cpp
file extension.
Those descriptions are a bit of an over-simplification. We’ll explore the nuances in coming sections.