Why non-equality check of one variable against many values always returns true?

Question

I have a variable v in my program, and it may take any value from the set of values

\"a\", \"b\", \"c\", ..., \"z\"

A

Answer 1

You could use something like this, for PHP:

if(strpos('xyz',$v[0])===false)//example 1
//strpos returns false when the letter isn't in the string
//returns the position (0 based) of the substring
//we must use a strict comparison to see if it isn't in the substring

if(!in_array($v[0],array('x','y','z')))//example 2

//example 3
$out=array('x'=>1,'y'=>1,'z'=>1); //create an array
if(!$out[$v[0]]) //check if it's not 1

if(!preg_match('/^[xyz]$/',$v))//example 4, using regex

if(str_replace(array('x','y','z'),'',$v[0]))//example 5


if(trim($v[0],'xyz'))//example 6

For Javascript:

if(~'xyz'.search(v[0]))//example 1(.indexOf() works too)

if(!(v[0] in {x:0,y:0,z:0}))//example 2

if(~['x','y','z'].indexOf(v[0]))//example 3, incompatible with older browsers.

if(!/^[xyz]$/.match(v))//example 4

if(v.replace(/^[xyz]$/))//example 5

For MySQL:

Select not locate(@v,'xyz'); -- example 1

select @v not in ('x','y','z'); -- example 2

-- repetition of the same pattern for the others

For C:

if(!strstr("xyz",v))//example 1, untested

There are more ways, I'm just too lazy.

Use your imagination and just write the one that you like more!