php array negative and positive numbers

Question

I have an array of values both positive and negative:

$numbers=['10','-2','-1','8','-7','1','-2','-3'];

I need to echo the results as:

numbers[0]=10;
numbers[1]=8;
numbers[2]=7;
numbers[3]=8;
numbers[4]=1;
numbers[5]=1;
numbers[6]=-1;
numbers[7]=-4;

Basically I take the first value that is always positive, echo that value, subtract the first negative value, echo the results, the second, etc until I found the next positive value, I echo that value, subtract from this value that becomes now reference the second negative value and so on...

I tries this in a loop but I can't manage to "break" the results after finding the second positive number - the numbers keep adding at the result from the first set of positive + negative values - even when using unset....

$i=0;
$sum=0;    
        
while ($i < count($numbers)){
            
    $sum=$sum+$numbers[i];
                    
                    
    if($numbers[i]>0)
    {
        echo $numbers[i];
    }
    else
    {
        echo $sum;
    }       
}

sorry - you're right - in my code there is $i++; after each echo but here it was lost during code formatting - I must have deleted it by mistake. Using foreach I have the same problem - how to "break" $sum at the next positive number... — GigiF
– GigiF, Commented Jan 4, 2023 at 23:08
Sorry - it was very late , I was very tired - I've seen this now and thank you - your solution works great! — GigiF
– GigiF, Commented Jan 5, 2023 at 16:11

Barmar · Accepted Answer · 2023-01-04 23:04:09Z

2

You need to reset $sum to the number whenever you get a positive number.

foreach ($numbers as $i => $num) {
    if ($num > 0) {
        $sum = $num;
    } else {
        $sum += $num;
    }
    echo "numbers[$i] = $sum<br>";
}

answered Jan 4, 2023 at 23:04

Barmar

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Comments

Wisdom Ighofose · Accepted Answer · 2023-01-04 23:26:54Z

1

$numbers=['10','-2','-1','8','-7','1','-2','-3'];

   $i=0;
   // there is no need initializing sum here since you it will be the first number
   $sum=0;    
    
    while ($i < count($numbers)){
        
   //  $sum=$sum+$numbers[$i]; This is not needed
    
   if ($numbers[$i] > 0) {
      // if the $numbers[$i] is greater than 0 then it is a positive number
      // you set $sum to the new positive number
        $sum = $numbers[$i];
    } else {
      //else you perform arithmetic function here 
      // and since $numbers[$i] is a negetive number adding it will substract from $sum
        $sum += $numbers[$i];
    }
   //  You're concern about the sum so you should do your logic before echoing 
      echo $sum; 
   // Always remember to increment as while loop wont do that for you        
      $i++;
   }

edited Jan 4, 2023 at 23:26

answered Jan 4, 2023 at 23:18

Wisdom Ighofose

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3 Comments

GigiF Over a year ago

Thank you for your comments- I learned from them. I was under the impression - from programming in C# that not initializing a variable before use is bad programming...php is different? Also solution works great - like the one above.

Barmar Over a year ago

@GigiF PHP has automatic default values, although it will still warn when you try to use an uninitialized variable. But which variable do you think is uninitialized?

GigiF Over a year ago

I was reffering at $sum=0; and the comment: "// there is no need initializing sum here since you it will be the first number"

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