Question

I have if statement with multiple condition,
what is the differece between this two conditon:
1.

    if($province=="AB" || "NT" || "NU" || "YT")
{
    $GST=5;
}
else if($province=="BC" || "MB")
{
    $GST=5;
    $PST=7;
}
else if($province=="NB" || "NF" || "ON")
{
    $HST=13;
}  

and second is:
2.

if($province=="AB" || $province=="NT" || $province=="NU" || $province=="YT")
{
    $GST=5;
}
else if($province=="BC" || $province=="MB")
{
    $GST=5;
    $PST=7;
}
else if($province=="NB" || $province=="NF" || $province=="ON")
{
    $HST=13;
}

Answer 1

The difference between the two is that the first one won’t work as expected, and the second is technically correct.

The code:

if($province=="AB" || "NT" || "NU" || "YT")

will always evaluate to true and execute the code in that conditional block.

The reason is because you are only checking if $province == "AB" and then you are checking if "NT" == true which will evaluate to true.

To check province against all of those values (AB, NT, NU, YT) you need to explicitly check $province against each value, not just the first, which is what you are correctly doing in the second example.