PHP arithmetic operation (addition)

Question

floor( 500 * (1.4 / 100) ) gives me 6 and floor( 500 * 1.4 / 100 ) gives me 7

Can anyone help me understand how PHP arithmetic works internally.

How can the second example give you 7 ? That doesn't seem possible to me. — Daan
– Daan, Commented Oct 15, 2015 at 12:09
I find it unlikely that 500 * 1.4 * 100 returns anything close to 7. — Luke Joshua Park
– Luke Joshua Park, Commented Oct 15, 2015 at 12:10
Is it a typo in the second example (the last *)? It meant to be ` floor( 500 * 1.4 / 100 )`, right? — Pred
– Pred, Commented Oct 15, 2015 at 12:10

Rafał Toboła · Accepted Answer · 2015-10-15 12:15:47Z

6

It works like in any other language. Try for example javascript:

    (500*(1.4 / 100)) // this will give you 6.999999999999999
    (500* 1.4 / 100)  // this will give you 7

The problem is, that PHP has internal setting which tells him about precission with which he displays float numbers. Try doing something like that:

    php > ini_set('precision', 17);
    php > echo ( 500 * (1.4 / 100) );
    6.9999999999999991
    php > echo ( 500 * 1.4 / 100 );
    7
    php >

I assume you've tried the code above without ini_set (using default settings – probably 14 as precision), and it returned you 7 in both results:

    php > echo ( 500 * 1.4 / 100 );
    7
    php > echo ( 500 * (1.4 / 100) );
    7
    php >

answered Oct 15, 2015 at 12:15

Rafał Toboła

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