Best way to format if statement with multiple conditions

If you want to some code to execute based on two or more conditions which is the best way to format that if statement ?

first example:-

if(ConditionOne && ConditionTwo && ConditionThree)
{
   Code to execute
}

Second example:-

if(ConditionOne)
{
   if(ConditionTwo )
   {
     if(ConditionThree)
     {
       Code to execute
     }
   }
}

which is easiest to understand and read bearing in mind that each condition may be a long function name or something.

Solution 1:

I prefer Option A

bool a, b, c;

if( a && b && c )
{
   //This is neat & readable
}

If you do have particularly long variables/method conditions you can just line break them

if( VeryLongConditionMethod(a) &&
    VeryLongConditionMethod(b) &&
    VeryLongConditionMethod(c))
{
   //This is still readable
}

If they're even more complicated, then I'd consider doing the condition methods separately outside the if statement

bool aa = FirstVeryLongConditionMethod(a) && SecondVeryLongConditionMethod(a);
bool bb = FirstVeryLongConditionMethod(b) && SecondVeryLongConditionMethod(b);
bool cc = FirstVeryLongConditionMethod(c) && SecondVeryLongConditionMethod(c);

if( aa && bb && cc)
{
   //This is again neat & readable
   //although you probably need to sanity check your method names ;)
}

IMHO The only reason for option 'B' would be if you have separate else functions to run for each condition.

e.g.

if( a )
{
    if( b )
    {
    }
    else
    {
        //Do Something Else B
    }
}
else
{
   //Do Something Else A
}

Solution 2:

Other answers explain why the first option is normally the best. But if you have multiple conditions, consider creating a separate function (or property) doing the condition checks in option 1. This makes the code much easier to read, at least when you use good method names.

if(MyChecksAreOk()) { Code to execute }

...

private bool MyChecksAreOk()
{ 
    return ConditionOne && ConditionTwo && ConditionThree;
}

It the conditions only rely on local scope variables, you could make the new function static and pass in everything you need. If there is a mix, pass in the local stuff.