Question

Consider these to options

if(successful)
{
    if(condition)
    {
       //do something
    }
    if(condition)
    {
       //do something
    }
    ...
}

or

if(successful)&&(condition)
{
   //do something
}
if(successful)&&(condition)
{
   //do something
}
...

Imagine there 100 if statements.

Is there any difference in efficiency?

Thanks in advance.

Answer 1

That all depends how costly it is to evaluate the successful expression.

You should also note that the two versions are not semantically equivalent as the evaluation of the if-expression might have side-effects¹.

If you are actually facing performance issues then measure, don’t guess. Measuring will be the only way to see what the performance really is.

¹To explain a question from the comments, here is a simple example where you would get different behavior:

The method CreateProcess has the side-effect of starting a new process and indicates the successful creation by returning true:

bool CreateProcess(string filename, out handle) { ... } 

if (CreateProcess("program.exe", out handle))
{   
    if (someCondition)
    {
         handle.SomeMethod(...);
    }
    if (someOtherCondition)
    {
         handle.SomeOtherMethod(...);
    }
}

This is quite different from the following:

if (CreateProcess("program.exe", out handle) && someCondition)
{
    handle.SomeMethod(...);
}
if (CreateProcess("program.exe", out handle) && someOtherCondition)
{
    handle.SomeOtherMethod(...);
}