Need exact reason for this logically condition failed

Question

Why below code is printing the "here", it should be "there"

$a = "171E-10314";
if($a == '0')
{
echo "here";
}
else
{
echo "there";   
}

according to the code, $a does not equal zero - it equals some strange string — Professor Abronsius, Nov 26 '15 at 16:19
@RamRaider the OPs issue is happening here - https://3v4l.org/Iv1mi — Sean, Nov 26 '15 at 16:21
"Even if you are comparing strings to strings, PHP will implicitly cast them to floats and do a numerical comparison if they appear numerical." - from http://stackoverflow.com/questions/3333353/string-comparison-using-vs-strcmp — Professor Abronsius, Nov 26 '15 at 16:29

Audite Marlow · Accepted Answer · 2016-01-14T16:09:13.383

5

PHP automatically parses anything that's a number or an integer inside a string to an integer. "171E-10314" is another way of telling PHP to calculate 171 * 10 ^ -10314, which equates to (almost) 0. So when you do $a == '0', the '0' will equate to 0 according to PHP, and it returns true.

If you want to compare strings, use the strcmp function or use the strict comparator ===.

edited Jan 14 '16 at 16:09

answered Nov 26 '15 at 16:28

Audite Marlow

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score 1 · Answer 2 · answered Nov 26 '15 at 16:50

when you use the == comparison, PHP tries to cast to different data types to check for a match like that

in your case:

'0' becomes 0
"171E-10314" is still mathematically almost 0 but I think PHP just rounds it to 0 due to the resolution of float.

check this link for a visual representation: http://www.wolframalpha.com/input/?i=171E-10314

score 0 · Answer 3 · edited Nov 26 '15 at 21:14

0

Use === /*(this is for the 30 character)*/

edited Nov 26 '15 at 21:14

Kirk Beard

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answered Nov 26 '15 at 16:22

Murat Cem YALIN

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I updated code to use ===, but any reason why 171E-10314 is equal to 0 – Inder Singh Nov 26 '15 at 16:22
read here http://stackoverflow.com/questions/3333353/string-comparison-using-vs-strcmp – Murat Cem YALIN Nov 26 '15 at 16:23

score 0 · Answer 4 · answered Nov 26 '15 at 16:29

0

As per the answers given I tried to convert the string into numerical:

$a = "171E-10314" + 0;
print $a;

And I got output as 0.

Thats why it is printing here.

answered Nov 26 '15 at 16:29

Dinesh Patra

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Need exact reason for this logically condition failed

4 Answers4