PHP: Nested For Loops

Derek Bridge

Department of Computer Science,
University College Cork

PHP: Nested For Loops

Aims:

• to practice writing programs with nested loops

Loops within loops

• In a for-loop

  for (expr1; expr2; expr3)
{
    zero, one or more statements
}

  the block can contain any kind of statement…including other loops
• Similarly, the bodies of foreach loops can contain other loops

Example of a nested loop

for ( $i = 0; $i < 4; $i++ )
{
    for ( $j = 0; $j < 3; $j++ )
    {
        echo "<p>i: {$i} j: {$j}</p>";
    }
}

Class exercises

1. Suppose mult.html contains this form:

   <form action="mult.php" method="get">
       <input type="text" name="number" />
       <input type="submit" />
   </form>

   Write mult.php, which outputs (as an HTML table) a set of multiplication tables ('times tables') for the number that the user enters. E.g. if the user enters 12, then your output runs from '1 times 1 is 1' up to '12 times 12 is 144'
2. Write a PHP script that outputs a 'diary' for the current year with one line per day

Observations

• Terminology: the outer loop and the inner loop
• Sometimes the nesting goes deeper
  • e.g. a loop within a loop within a loop
• The diary example illustrates an interesting but common situation:
  • a variable from the outer loop is used as either the start or (as here) the end value of the loop variable of the inner loop