Whitespace and basic formatting

Whitespace is a term that refers to characters that are used for formatting purposes. In C++, this refers primarily to spaces, tabs, and (sometimes) newlines. The C++ compiler generally ignores whitespace, with a few minor exceptions.

Consequently, the following statements all do the exact same thing:

cout << "Hello world!";

cout <<                "Hello world!";

cout <<                    "Hello world!";

cout <<       "Hello world!";

Even the last statement with the newline in it compiles just fine.

The following functions all do the same thing:

int add(int x, int y) { return x + y; }

int add(int x, int y) {
    return x + y; }

int add(int x, int y)
{    return x + y; }

int add(int x, int y)
{
    return x + y;
}

One exception where the C++ compiler does pays attention to whitespace is inside quoted text, such as "Hello world!".

"Hello world!"

is different than

"Hello     world!"

and each prints out exactly as you’d expect. Newlines are not allowed in quoted text:

cout << "Hello
     world!" << endl; // Not allowed!

Another exception where the C++ compiler pays attention to whitespace is with // comments. Single-line comments only last to the end of the line. Thus doing something like this will get you in trouble:

cout << "Hello world!" << endl; // Here is a single-line comment
this is not part of the comment

Basic formatting

Unlike some other languages, C++ does not enforce any kind of formatting restrictions on the programmer (remember, trust the programmer!). Many different methods of formatting C++ programs have been developed throughout the years, and you will find disagreement on which ones are best. Our basic rule of thumb is that the best styles are the ones that produce the most readable code, and provide the most consistency.

Here are our recommendations for basic formatting:

1) Your tab should be set to 4 spaces.

2) The braces that tell where a function begins and ends should be aligned with the function name, and be on their own lines:

int main()
{
}

3) Each statement within braces should start one tab in from the opening brace of the function it belongs to. For example:

int main()
{
    cout << "Hello world!" << endl;
    cout << "Nice to meet you." << endl;
}

4) Lines should not be too long. Typically, 72, 78, or 80 characters is the maximum length a line should be. If a line is going to be longer, it should be broken (at a reasonable spot) into multiple lines by indenting with a double tab.

int main()
{
    cout << "This is a really, really, really, really, really, really, really, " <<
            "really long line" << endl;
    cout << "This one is short" << endl;
}

5) If a long line that is broken into pieces is broken with an operator (eg. << or +), the operator should be placed at the end of the line, not the start of the next line:

    cout << "This is a really, really, really, really, really, really, really, " <<
            "really long line" << endl;

Not

    cout << "This is a really, really, really, really, really, really, really, "
            << "really long line" << endl;

This makes it more obvious from looking at the first line that the next line is going to be a continuation.

6) Use whitespace to make your code easier to read.

Harder to read:

nCost = 57;
nPricePerItem = 24;
nValue = 5;
nNumberOfItems = 17;

Easier to read:

nCost          = 57;
nPricePerItem  = 24;
nValue         = 5;
nNumberOfItems = 17;

Harder to read:

cout << "Hello world!" << endl; // cout and endl live in the iostream library
cout << "It is very nice to meet you!" << endl; // these comments make the code hard to read
cout << "Yeah!" << endl; // especially when lines are different lengths

Easier to read:

cout << "Hello world!" << endl;                  // cout and endl live in the iostream library
cout << "It is very nice to meet you!" << endl;  // these comments are easier to read
cout << "Yeah!" << endl;                         // especially when all lined up

Harder to read:

// cout and endl live in the iostream library
cout << "Hello world!" << endl;
// these comments make the code hard to read
cout << "It is very nice to meet you!" << endl;
// especially when all bunched together
cout << "Yeah!" << endl;

Easier to read:

// cout and endl live in the iostream library
cout << "Hello world!" << endl;

// these comments are easier to read
cout << "It is very nice to meet you!" << endl;

// when separated by whitespace
cout << "Yeah!" << endl;

We will follow these conventions throughout this tutorial, and they will become second nature to you. As we introduce new topics to you, we will introduce new style recommendations to go with those features.

Ultimately, C++ gives you the power to choose whichever style you are most comfortable with, or think is best. However, we highly recommend you utilize the same style that we use for our examples. It has been battle tested by thousands of programmers over billions of lines of code, and is optimized for success.