How to Use C++ Expressions

What is a C++ Expression or a Statement?

Feb 21, 2009

Any C++ program consists of a series of expressions and statements, but what exactly are they?

The starting point for any C++ program is simply a sequence of statements typed into a text file by a programmer. These statements are (mainly) free-form, so that they can be laid out in ways that the programmer feels may highlight the code. The only real restriction is that a semi-colon (;) must be used to end any statement.

Laying out C++ Code

The actual layout of the code that makes up a program is ignored by the compiler, but not by the preprocessor. This means that any statements to be used by the preprocessor must be laid out on separate lines:

int

main

()

{

cout

"Code all on separate lines"

;

}

The only real consideration, therefore, is how easy the code is to read by humans and not by computers:

int main () {

cout <<"Make the code easy to read";

}

The only real rule is to choose a style that is easy to read and then stick to it.

Writing C++ Statements: Operators and Operands

A typical C++ statement contains operators and operands. Operators are the key words and symbols used to carry out operations, for example:

These are used in conjunction with operands. Operands are the variables that the operators operate on. Combined they produce something like:

int choice;

const int target = 7;

cout << "Please enter 1 - 10:";

cin >> choice;

if (choice == target) cout << "Correct";

In this case the equals operator has been used with two operands (choice and target) in a simple if statement. Of course most programs require something a little more complex than that.

C++ Compound and Nested Statements

Each individual statement ends in a semi-colon. However, statements can be grouped together into a single (compound) statement by making use of braces (or curly brackets - {}). This also allows one statement to be nested inside another:

while (choice != target) {

cout << "Please enter 1 - 10:";

cin >> choice;

if (choice > target) {

cout << "Too big\n";

} else if (choice < target) {

cout << "Too small\n";

} else {

cout << "Correct";

}

In this example series of if..then..else statements have been nested in a compound statement (within the when statement). This idea of nesting can be seen more clearly by extending the if statements further:

const int max = 10;

const int way_out = 100;

if (choice > target) {

cout << "Too big\n";

if (choice > max ) {

cout << "Much too big\n";

if (choice >= way_out ) {

cout << "Really, really far out\n";

}

With just these few statements the programmer can create a very simple yet effective program.

Summary

Even the most complex program can be created by just these simple building blocks.

The copyright of the article How to Use C++ Expressions in C Programming is owned by Mark Alexander Bain. Permission to republish How to Use C++ Expressions in print or online must be granted by the author in writing.