for loop

A much neater and safer way to implement a loop structure is using the “for” statement. This isn’t much different from a while statement, in fact there is nothing you cannot achieve when using for statement that you cannot do with a while statement.

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The basic for loop syntax is shown below:

for (intialization; condition; increment) {
code to be executed;
}

The for statement includes three parameters. The first parameter is used to initialize variables, the second holds the condition, and the third parameter contains any increments required to implement the loop. The code block associated with the for statement is always enclosed within the { opening and } closing brace symbols.

The following example demonstrates a for loop that displays the message "Welcome to PHP" 4 times:

In the above example, the for loop includes three parameters that perform the following task:

1. The variable $counter is intialized to 1
2. $counter < 5 establishes the condition that must be true for the loop to execute
3. $counter++ increments the variable $counter each time the loop runs

Below is the output generated by the sample loop:

Welcome to PHP
Welcome to PHP
Welcome to PHP
Welcome to PHP

During the first run, the value of $counter is initialized to 1. Since 1 is less than 5, $counter is incremented to 2. Next, the echo statement is used to display the string "Welcome to PHP". A <br/> is concatenated to the display to create a carriage return each time the loop is processed. During the second iteration, the value of $counter is equal to 2. Since 2 is less than 5, the echo statement again displays the string "Welcome to PHP". This process continues while the value of $counter is 3 and 4. When $counter is equal to 5, the condition is no longer true and the while loop ends.

for loops are also used as a convenient way to iterate through the values of an array. Recall from tutorial 3 that arrays consists of elements and indexes. Each element has an associated index. The first index of a numerically indexed array is 0. Until now, when printing array elements, it was necessary to print each element separately. For large arrays this can be very time consuming and cumbersome. for loops solve this problem. In the following example, an array containing 5 elements is created. Next, a for loop is used to display each of the array values.

The $colors array contains five elements - $colors[0] = "red", $colors[1] = "green", $colors[2] = "blue", $colors[3] = "yellow", and $colors[4] = "white". A for loop is created; the counter variable $i is initially set to 0 to correspond with the first element of the array. Next, the condition is set by checked to see if the value of the counter, $i, is less than sizeof($colors) or the total number of elements in the array. Here we know the size of the array is 5, however, in most cases the size of the array at runtime is unknown. Finally, the counter variable is incremented by 1 during each iteration. Each time the loop runs, the string - "Array value $i+1 is $colors[$i] is displayed. The values of $i+1 and $colors[$i] are expanded and produce literal values when printed. The loop runs until the the counter exceeds the number of elements or the size of the array. The output is show below:

Array value 1 is red.
Array value 2 is green.
Array value 3 is blue.
Array value 4 is yellow.
Array value 5 is white.

Loops are useful constructs that will be used extensively throughout future tutorials.