Loop Terminology
In the previous section we encountered several new terms. Let’s look at these more formally, so that you’ll understand them well when working with loops:
- Initialization
The statement or expression that defines one or more variables used in the test expression of a loop.
- Test expression
The condition that must be met in order for the substatements in the loop body to be executed. Often called a condition or test, or sometimes,
control
.
- Update
The statements that modify the variables used in the test expression before a subsequent test. A typical update statement increments or decrements the loop’s counter.
- Iteration
One complete execution of the test expression and statements in the loop body. Sometimes referred to as one loop or one pass.
- Nesting or nested loop
A loop that contains another loop so that you can iterate through some sort of two-dimensional data. For example, you might loop through each row in a column for all the columns in a table. The outer or top-level loop would progress through the columns, and the inner loop would progress through the rows in each column.
- Iterator or index variable
A variable whose value increases or decreases with each iteration of a loop, usually used to count or sequence through some data. Loop iterators are often called counters. Iterators are conventionally named
i
,j
, andk
or sometimesx
,y
, andz
. In a series of nested loops,i
is usually the iterator of the top-level loop,j
is the iterator of the first nested loop, ...
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