Notes

The most common type of instruction in a program is the statement. A statement in C++ is the smallest independent unit in the language. In human language, it is analogous to a sentence. We write sentences in order to convey an idea. In C++, we write statements in order to convey to the compiler that we want to perform a task. Statements in C++ are terminated by a semicolon





int x;
x = 5;
std::cout << x;


int x is a declaration statement. It tells the compiler that x is a variable. You may remember variables from algebra in school. Variables serve the same purpose here: to provide a name for a value that can vary. All variables in a program must be declared before they are used. We will talk more about variables shortly.

x = 5 is an assignment statement. It assigns a value (5) to a variable (x).

std::cout << x; is an output statement. It outputs the value of x (which we set to 5 in the previous statement) to the screen.

The compiler is also capable of resolving expressions. An expression is a mathematical entity that evaluates to a value. For example, in math, the expression 2+3 evaluates to the value 5. Expressions can involve values (such as 2), variables (such as x), operators (such as +) and functions (which return an output value based on some input value). They can be singular (such as 2, or x), or compound (such as 2+3, 2+x, x+y, or (2+x)*(y-3)).

For example, the statement x = 2 + 3; is a valid assignment statement. The expression 2+3 evaluates to the value of 5. This value of 5 is then assigned to x.

In C++, statements are typically grouped into units called functions. A function is a collection of statements that executes sequentially. Every C++ program must contain a special function called main. When the C++ program is run, execution starts with the first statement inside of function main. Functions are typically written to do a very specific job. For example, a function named “max” might contain statements that figures out which of two numbers is larger. A function named “calculateGrade” might calculate a student’s grade. We will talk more about functions later.

A library is a collection of precompiled code (e.g. functions) that has been “packaged up” for reuse in many different programs. Libraries provide a common way to extend what your programs can do. For example, if you were writing a game, you’d probably want to include a sound library and a graphics library.

The C++ core language is actually very small and minimalistic (and you’ll learn most of it in these tutorials). However, C++ also comes with a library called the C++ standard library that provides additional functionality for your use. One of the most commonly used parts of the C++ standard library is the iostream library, which contains functionality for writing to the screen and getting input from a console user.

#include <iostream>

int main()
2 {
std::cout << "Hello world!";
return 0;
5 }

Line 3 declares the main() function, which as you learned above, is mandatory. Every program must have a main() function.

Lines 2 and 5 tell the compiler which lines are part of the main function. Everything between the opening curly brace on line 2 and the closing curly brace on line 5 is considered part of the main() function.

A statement is a “complete sentence” that tells the compiler to perform a particular task. An expression is a mathematical entity that evaluates to a value. Expressions are often used inside of statements.

A function is a collection of statements that executes sequentially, typically designed to perform a specific job. A library is a collection of functions packaged for use in multiple programs.

What symbol do statements in C++ end with?
Answer
The semicolon (;)

A syntax error is a compiler error that occurs at compile-time when your program violates the grammar rules of the C++ language.