Böhm-Jacopini Counter (BJC)

Count sequence, selection, iteration structures for code analysis

The Böhm-Jacopini Counter (BJC) is a metric that measures the structural composition of code based on the Structured Program Theorem. This theorem states that any algorithm can be constructed using only three control structures:

• Sequence: A series of statements executed in order.
• Selection: Decision-making structures (e.g., if, else, switch).
• Repetition: Looping structures (e.g., for, while).

The BJC provides a tuple (s, e, i) representing the count of sequence blocks (s), selection constructs (e), and iteration constructs (i) in a given piece of code.

Example Output

For the following PHP function:

function factorial(int $n): float|false
{
  if ($n < 0) {
    $result = false;
  } else {
    $result = 1.0;
    for ($i = 1; $i <= $n; $i++) {
      $result *= $i;
    }
  }

  return $result;
}

A BJC analysis would yield the following output:

Array
(
    [sequence] => 6
    [selection] => 1
    [repetition] => 1
)

This indicates that the function contains 6 sequence blocks, 1 selection constructs (if), and 1 repetition construct (the for loop).