The main issues of code quality with if-then-else, switch, and select case are proper indentation and the use of curly braces in C. Improperly indented code, and code that does not use curly braces for nested ifs, can be easily misread. Use of curly braces is often a good idea even if they are not needed to group multiple statements, since they can clarify the code.

    // Misleading
    if ( x == 1 )
        if ( y == 2 )
            z = 3;
    else            // Belongs to if ( y == 2 ), not if ( x == 1 )
        z = 4;
        

    // Clearer
    if ( x == 1 )
        if ( y == 2 )
            z = 3;
        else
            z = 4;
        

    // Clearest
    if ( x == 1 )
    {
        if ( y == 2 )
            z = 3;
        else
            z = 4;
    }