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PHP

Posted by nicholas maddren
nicholas maddren
12,793 Points

Understanding This Code

I had this code in the PHP quiz:

$numbers = array(1,2,3,4);

$total = count($numbers);

$sum = 0;

$output = "";

$i = 0;

foreach($numbers as $number) {

$i = $i + 1;

if ($i < $total) {

    $sum = $sum + $number;

}

}

echo $sum;

Can someone explain this to me? Why does it echo 6? I just dont know where that value has came from. Thanks any help would be great I just want to understand it a little better :)

2 Answers

Ivan Uvarov
Ivan Uvarov
22,403 Points
Ivan Uvarov
Ivan Uvarov
22,403 Points

Ok, originally $total = 4 (the number of elements in the array), $sum = 0, and $i = 0. Then you execute a loop 4 times - 1 for each element of the array:

  1. When loop executes first time, $number = 1 (the first element in the array). Then you add 1 to $i, and as a result $i = 0 + 1 = 1. As $i (1) is less than $total (4), you add $number (1) to the sum, and now $sum = 1;
  2. $number = 2 (the second element in the array). $i = 2. As $i (2) is less than $total (4), you add $number (2) to the sum, and now $sum = 3;
  3. $number = 3 (the third element in the array). $i = 3. As $i (3) is less than $total (4), you add $number (3) to the sum, and now $sum = 6;
  4. $number = 4 (4th element in the array). $i = 4. Then you check condition: now $i (4) is not less than $total (4), so you don't execute code inside the condition. Also, you reached last element in the array, so you exit the loop.

Now you output $sum, which was equal to 6 after the last change.

Kenneth Camilleri
Kenneth Camilleri
7,816 Points
Kenneth Camilleri
Kenneth Camilleri
7,816 Points

Here's a dry run of the program.

  1. $total becomes 4 because there are 4 elements in the $numbers array (The elements are 1, 2, 3 and 4)
  2. $i is set to 0; it is the string index that will be used to loop through the elements
  3. $i increments to 1. $i is less than 4 ($total), so the IF statement is entered
  4. $sum is 0. $number at this point is equal to 1, so now, the sum is 0 + 1 = 1
  5. $i increments to 2. $i is less than 4, so the IF statement is entered
  6. $sum is 1. $number at this point is equal to 2, so now the sum is 1 + 2 = 3
  7. $i increments to 3. $i is less than 4, so the IF statement is entered
  8. $sum is 3. $number at this point is equal to 3, so now the sum is 3 + 3 = 6
  9. $i increments to 4. $i is EQUAL to 4, so the IF statement is NOT entered and the foreach loop finishes since that was the last element. 4 is NOT added to the sum
  10. The final output is sum, which is 6

Dry runs, while cumbersome, will always help you understand a program, or even catch out logical errors in programs.