Single '=' and double '=='?

Question

i'm doing some programming..

i know single '=' means we assign value into a variable..

and double '==' means equal....

but i am confused to compare those..

let say, i have a 'login.html' + javaScript page with 2 textfield..

which is username and password...

i want to compare if those textfield are not empty..

how should i do?

either

======================================...

if((username = "") && (password = ""))

======================================...

or

======================================...

if((username == "") && (password == ""))

======================================...

please help me!!

thanx in advance =)

Answer 1

If you want to compare anything then use == and if you want to asign something to variable then use = sign

http://milindkansagara1984.blogspot.com

Answer 2

I will try as non-technical as a can, to describe this:

The difference is like remembering that its raining outside vs asking if it is raining outside... make sense?

= will STORE data FROM the right side INTO the variable on the left side of the expression.

== will COMPARE the data FROM the right side TO the data on the left side of the expression and EVALUATE the expression to True OR False.

Answer 3

use == (double equal sign)

single "=" is an assignment operator

double "=" is a comparison operator

Answer 4

An 'if' statement needs to evaluate to a boolean value (i.e. true or false). This implies "==" be used, which can only evaluate to a boolean result. The problem is that many early languages allowed a zero value of an expression be evaluated as 'false' and any nonzero as 'true'. This is why using "=" in the 'if' doesn't cause a syntax error in C and other early languages. More recent languages (C#, for example) are stricter in their variable typing and eliminate the problem.

The best way to avoid the problem (other than a strict-typing language) is never use the shortcut and instead always explicitly check a boolean condition: "If 'if', equals-equals".

Answer 5

well,

"=" makes "a" equivalent to "b"

"==" checks if a is equivalent to b,

so if you put a while(a=b) than while(a==b), then it'll be an infinite while loop until b becomes zero, w/c is pretty weird

Answer 6

"=" is = "equal to" but (matches similiar string)

"==" is = "Exactly equal to" (matches exact string

see this for more clear http://developerskb.blogspot.com