9.3 Sequence operator

General discussion

The sequence (or comma) operator is used to separate items. It has several uses, four of which are listed then demonstrated:

1. To separate identifier names when declaring variables or constants
2. To separate several parameters being passed into a function
3. To separate several initialization items or update items in a for loop
4. Separate values during the initialization of an array

This first example is often seen in textbooks, but this method of declaring variables is not preferred. It is difficult to quickly read the identifier names.

int pig, dog, cat, rat;

The following vertical method of declaring variables or constants is preferred.

The data types and identifier names (known as parameters) are separated from each other. This example is a function prototype.

double area_trapezoid(double base, double height, double top);

In the syntax of a for loop you have three parts each separated by a semi-colon. The first is the initialization area which could have more than one initialization. The last is the update area which could have more than one update. Mutiple initializations or updates use the comma to separate them. This example is only the first line of a for loop.

for(x = 1, y = 5; x<15; x++, y++)

The variable ages is an array of integers. Initial values are assigned using block markers with the values separated from each other using a comma.

int ages[] = {2,4,6,29,32};

Definitions

sequence

An operator used to separate multiple occurrences of an item.