Question

An example using the Conditional Operator.

void setSelected( bool selected )
{
    a = selected? SELECTED_VALUE_A: DEFAULT_VALUE_A;
    b = selected? SELECTED_VALUE_B: DEFAULT_VALUE_B;
    c = selected? SELECTED_VALUE_C: DEFAULT_VALUE_C;
}

An example using an if and temporaries.

void setSelected( bool selected )
{
    a = DEFAULT_VALUE_A;
    b = DEFAULT_VALUE_B;
    c = DEFAULT_VALUE_C;
    if ( selected )
    {
        a = SELECTED_VALUE_A;
        b = SELECTED_VALUE_B;
        c = SELECTED_VALUE_C;
    }
}

An example using functions

void setLook( int nA, float nB, std::string nC )
{
    a = nA;
    b = nB;
    c = nC;
}

void setSelected( bool selected )
{
    if ( selected )
        setLook( DEFAULT_VALUE_A, DEFAULT_VALUE_B, DEFAULT_VALUE_C );
    else
        setLook( SELECTED_VALUE_A, SELECTED_VALUE_B, SELECTED_VALUE_C );
}

An alternate example using functions. Still uses setLook

void setLookSelected()
{
    setLook( SELECTED_VALUE_A, SELECTED_VALUE_B, SELECTED_VALUE_C );
}
void setLookNormal()
{
    setLook( DEFAULT_VALUE_A, DEFAULT_VALUE_B, DEFAULT_VALUE_C );
}
void setSelectedAF( bool selected )
{
    if ( selected )
        setLookSelected();
    else
        setLookNormal();
}
//Or just call
setLookSelected();
setLookNormal();

Answer 1

Let’s simplify the requirement:

Set variable a to c if b is true or d otherwise

Using the conditional operator:

a = b ? c : d;

IMHO, as clear as it can get

Using temporaries and if:

a = c;
if (b)
   a = d;

Really ugly. You assign c to a, even if !b. Besides the awful readability, you encounter performance drop, as you have a double assignment. The optimizer could take care of that, but don’t count on it.

Using functions:

void setA(T x)
{
   a = x;
}

//....

if (b)
   setA(c);
else
   setA(d);

This could be useful if you have a lot of members that you want to set. Code maintenability will be improved. You’d only need to change in one place if you want different functionality. Not bad!

Alternate functions:

void setAC()
{
   a = c;
}
void setAD()
{
   a = d;
}

//...

if (b)
   setAC();
else
   setAD();

Another option I’d advise against. What if you don’t want to check only for b in the future? What if the two variants aren’t exclusive, i.e. you want to combine ID_NODE_GLOW_SELECT with ID_NODE_COLOR_NORMAL for some other condition?

Conclusion: I’d use the first variant for simple, small cases, and the functions with parameters for large classes, where you set a lot of members. I’d definetely stay away from options 2 & 4.