2.3. Repeating Actions with Loops

Loops are used frequently in scripts to set up a block of statements that repeat. The loop can repeat a specified number of times. For example, a loop that echoes all the state capitals in the United States needs to repeat 50 times. Or the loop can repeat until a certain condition is met. For example, a loop that echoes the names of all the files in a directory needs to repeat until it runs out of files, regardless of how many files there are. Here are three types of loops:

  • A for loop: Sets up a counter; repeats a block of statements until the counter reaches a specified number

  • A while loop: Sets up a condition; checks the condition, and if it's true, repeats a block of statements until the condition becomes false

  • A do..while loop: Sets up a condition; executes a block of statements; checks the condition, and if it's true, repeats the block of statements until the condition becomes false

We describe each of these loops in detail in the following few sections.

2.3.1. Using for loops

The most basic for loops are based on a counter. You set the beginning value for the counter, set the ending value, and set how the counter is incremented each time the statement block is executed.

2.3.1.1. Building for loops

The general format of a basic for loop is as follows:

for (startingvalue;endingcondition;increment)
{
    block of statements;
}

Within the for statement, you need to fill in the following values:

  • startingvalue: The startingvalue is a statement that ...

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