When I discuss flood fill algorithm in computer graphics and animation course with my professor, he say something about AndAlso operator (The AND logical operator that will not evaluate right side value if the left side value is true) that only exists in Visual Basic language. The code is something like this

void fill(pixels, x, y, color)
{
// If you call get_color on x < 0, it will be out of bound error
// Using AndAlso, if x is less than 0, it will not execute the
// get_color function
if(x >= 0 AndAlso get_color(pixels, x - 1, y) != color)
{
fill(pixels, x - 1, y, color)
}
...
}


But, when I check on some website, I found something interesting, it seems that the "most known" AND operator is AndAlso and you can also use "unpopular" bitwise AND operator.

From Wikipedia

Short-circuit evaluation, minimal evaluation, or McCarthy evaluation (after John McCarthy) is the semantics of some Boolean operators in some programming languages in which the second argument is executed or evaluated only if the first argument does not suffice to determine the value of the expression: when the first argument of the AND function evaluates to false, the overall value must be false; and when the first argument of the OR function evaluates to true, the overall value must be true.

## AND operator

In short circuit AND operation, if left value of AND operator is false, then the condition will be false without having to evaluate the value on the right side.

Value on the left side
|
v
false  &&  true/false  =  false
^              ^
|              |
Value on the right side.    |
Not evaluated!              |
No matter the value on the right side,
as long as the value on the left side
is false, the result will be false.


Example

bool left()
{
printf("This is left side\n");
return false;
}

bool right()
{
printf("This is right side\n");
return true; // or false, whatever you like.
}

...

if (left() && right())
{
...
}
...


Output

This is left side


But, if the left value is true, then the program will have to evaluate the value on the right side.

Value on the left side
|
v
true  &&  true/false  =  true/false
^               ^
|               |
Value on the right side.     |
|
If the right side value
is true, then the result
will be true. Vice-versa


If the right side value is true, then the result will be true. Vice-versa

## OR operator

The short circuit applies the same rule with the AND operator, but inverted.

If the left side is false, then it will not evaluate the expression on the right side and the condition will be false. But if the left side is true, then it will evaluate the expression on the right side as it become required to know the predicate result.

Value on the left side
|
v
true  ||  true/false  =  true
^             ^
|             |
Value on the right side.   |
Not evaluated!             |
No matter the value on the right side,
as long as the value on the left side
is true, the result will be true.

Value on the left side
|
v
false  ||  true/false  =  true/false
^                ^
|                |
Value on the right side.      |
|
If the right side value
is false, then the result
will be false. Vice-versa


## The Truth

So, actually

#include <cstdio>

bool is_even(int val)
{
return val % 2 == 0;
}

bool is_divisible_by_3(int val)
{
return val % 3 == 0;
}

int main()
{
int a;
scanf("%d", &a);

if (is_even(a) && is_divisible_by_3(a))
{
printf("Nice\n");
}
}


is identic with

#include <cstdio>

bool is_even(int val)
{
return val % 2 == 0;
}

bool is_divisible_by_3(int val)
{
return val % 3 == 0;
}

int main()
{
int a;
scanf("%d", &a);

if (is_even(a))
{
if(is_divisible_by_3(a))
{
printf("Nice\n");
}
}
}


You can compare the generated assembly here https://godbolt.org/z/YePZ8F

It will be very fatal if you have a required side effect (e.g write a log) from both left and right value when you are using short circuit operator or if are not using short circuit operator when the evaluation of right side value is depends on the left side value

array = [1, 2, 3];
index = 10;
// Will be error without short circuit
if(out_of_bounds(array, index) & is_even(array[index]))
{
...
}


## Fun Fact

Edsger W. Dijkstra criticized the short circuit operator

The conditional connectives — "cand" and "cor" for short — are ... less innocent than they might seem at first sight. For instance, cor does not distribute over cand: compare

(A cand B) cor C with (A cor C) cand (B cor C);

in the case ¬A ∧ C , the second expression requires B to be defined, the first one does not. Because the conditional connectives thus complicate the formal reasoning about programs, they are better avoided.

http://www.cs.utexas.edu/users/EWD/ewd10xx/EWD1009.PDF

Checkout Short-circuit evaluation - Rosetta Code to see the list of programming language that supports short-circuit evaluation.