Some disturbing signs I don't understand in programming

Question

1. What does "&" mean in JavaScript and how can it be compared to "&&".

2. What does "!" mean in JavaScript and how does it affect a parameter?

3. What is the difference between "++a" and "a++" and how is it possible that in some occasions, their values could output different results?

And finally, what does "+=" mean in JavaScript?

Answer 1

& is bitwise and:

00001000 (8)
& 01011000 (58)
--------
= 00001000 (8)

&& is logical and:

true && true = true
true && false = false

! is negation:

!true = false
!false = true

++a: increment a first, then use its value
a++: use a's value first, then increment it

a += b is the same as a = a + b

Answer 2

Bitwise and means that the binary representations of two numbers are compared bit by bit. If both are 1, the "sum" is 1, otherwise it is 0.

11010101
+
00101011
=
00000001

10111100
+
11010010
=
10010000

11110101
+
11111100
=
11110100

and so on... It's not something you'll need every day...

Answer 3

Anna Well said indeed!

Mofey As indicated already, logical operators (&& and ||) simply evaluate whether or not one, both, or neither boolean values are true.

Bitwise operators require an understanding of binary numbers and binary arithmetic.

A bitwise AND (&) will result in a new binary value where the bits are set if the corresponding bits of both operands are set to 1.

Example #1:
- Binary: 0101 & 1101 is 0101
- Integer: 5 & 13 is 5 which is truthy.

Example #2:
- Binary: 1001 & 0110 is 0000
- Integer: 9 & 6 is 0 which is falsey.

A bitwise OR (|) will result in a new binary value where the bits are set if either of the corresponding bits from the operands are set to 1.

Example #1:
- Binary: 0101 | 1100 is 1101
- Integer: 5 | 12 is 13 which is truthy.

Example #2:
- Binary: 1001 | 0110 is 1111
- Integer: 9 | 6 is 15 which is truthy.

Example #3:
- Binary: 1001 | 0000 is 0000
- Integer: 9 | 0 is 0 which is falsey.

Answer 4

Mofey You may be referring to the Conditional Ternary Operator which would follow a format like this:

let x = bool_expr ? a : b;

This is shorthand for the if/else statement:

let x;

if(bool_expr) {
x = a; //assignment when true
} else {
x = b; //assignment when false
}

Answer 5

Wow, your answer is excellent. I now understand better but Anna I still don't seem to get the "&". Please give me more info on that

Answer 6

Just one more sign I don't seem to understand in JavaScript ("?"). Please Anna and David Carroll help me with a definition for that sign in JavaScript, what it is called and its function.

Answer 7

Exactly, something like that Sir. So David Carroll, does that mean the operator is only an alternative for the if/else statement?

Answer 8

Yep. It's common in several languages.