Looping and branching examples

This page contains some PHP examples that use loops and if/else code.

The 3N+1 Problem
For N>0, repeatedly applying the following rules will lead to a series of integers that eventually converges at 1: If N is even, divide it by 2; if N is odd, multiply it by 3 and add 1. Write a PHP script to illustrate this problem.

Algorithm
1. Assign N a value > 1. 2. Loop while N > 1: 3.   Print N. 4.    If N is even 5.       N = N / 2 6.   Else 7.       N = 3 * N + 1 8. Done.

PHP Code
 1) { echo "$n"; if ($n % 2 == 0) { $n = $n / 2; } else { $n = 3 * $n + 1; } }

?>

Click here for a ThreeNPlus1 solution.

The 3N+1 Form
This problem would be more interesting if the user could input the value of N rather than having it set in the program.

HTML Form
 N:     Click here for an example that creates a ThreeNPlus1 form solution.