条件最佳实践[重复]

I have the following functions:

if(A==B)
{
  //do stuff
}

if(C==B)
{
  //do stuff
}

if(A==B)
   {
      //do stuff
   }
   else if(C==B)
   {
     //do stuff
}  

What is the difference between these two? I get the meaning of it but I have seen programmers prefer the first one instead of the 2nd one? why?

I personally prefer the 2nd one.

</div>

That's mostly a question of preference. I saw many programmers using both cases regardless of the actual function.

But correctly use the first case if you want both conditions to be chekced absolutely, the second one as a nested condition.

In the first case, both will be executed which makes it slower than the second one, as it checks only for the elseif, if the if condition is false

$var = 1;

if($var+1 ==2)
{
  echo "test1";
}

if($var-0==1)
{
  echo "test2";
}


if($var+1==2)
{
    echo "test1";
}
else if($var-0==1)
{
    echo "test2";
}

will output

test1test2test1

so we see, that number 2 ignores the elseif, which makes it faster.

In the first condition both the statements are excecuted because they are independent to each other, so all of them will be tested.

if(A==B)
{
  //do stuff
}

if(C==B)
{
  //do stuff
}

In second else if is just a nested if inside an else, so only one will of them will be tested, either if or elseif

if(A==B)
{
  //do stuff
}
else if(C==B)
{
  //do stuff
}

Not the same.

else if (C==B) will not be executed (even if C equals B) if the first condition was true.

without "else", just if (C==B) will be executed even if the first condition was true (in that case A==C :)

If only one variable is equal and need to run the same code regardless, it is better to use the first code so there is no loss of performance. But if you need to run different code depending on your variable, then the second is better.