Clever Geek Handbook

What's the difference between if (A) if (B) and if (A and B)?

if(A) then if(B)

against

if(A and B)

Which is the best to use and why?

+3


source to share


3 answers


Given:

if (a) {
  if (b) {
    /// E1
  }
  /// E2
} else {
  // E3
}

It might be tempting to replace it with:



if (a && b) {
 /// E1
} else {
 // E3
}

but they are not equivalent (a = true and b = false shows a counter argument for it)

Also, there is no reason not to link them if the language allows short-circuiting operations like AND, OR. And most of them allow it. The expressions are equivalent and you can use chaining to improve the readability of your code.

+5


source


It depends on your specific case, but usually:

1) if (A and B)

looks better / cleaner. It will immediately clear that the next block will be executed if the A

and tags are applied B

.

2) if(A) then if(B)

better when you want to do something, when applied A

, but B

not. In other words:



if (A):
    if (B):
        # something
    else:
        # something else

usually looks better than

if (A and B):
    # something
if (A and not B):
    # something else
+4


source


You noted this "algorithm" and "logic" and from that point of view I would say a little difference.

However, in practical programming languages, there may or may not be an issue of efficiency (or even feasibility).

Programming languages ​​such as C, C ++, and Java ensure that an expression A && B

is evaluated first A

, and if false is B

not evaluated. This can make a big difference if it B

is expensive compared to a calculator or invalid if it A

is false.

Consider the following piece of C code:

int*x
//....
if(x!=NULL&&(*x)>10) {
//...

Assessment (*x)

when x==NULL

very likely to result in a fatal error.

This "trick" (called short-circuit estimation) is useful because it avoids having to write a little more verbose:

if(x!=NULL){
  if((*x)>10){

Older versions of VB, such as VB6, are notorious for not making short circuits.

Another is that B

in A || B

will not be evaluated if A

true.

Support discussion:

Do all programming languages ​​have a boolean short circuit rating?

In any language that provides short-circuiting and has an optimizing compiler, you can assume that there is hardly any difference in code efficiency and go with the most readable ones. Usually it is if(A&&B)

.

+2


source






More articles:


All Articles