if/else and if/elseif

Question

If I have a statement block like this:

if (/*condition here*/){ }
else{ }

or like this:

if (/*condition here*/)
else if (/         


        

Answer 1

Many languages have a grammer like this (here: ECMAScript Language Specification, so JavaScript):

IfStatement :
    if ( Expression ) Statement else Statement
    if ( Expression ) Statement

Statement :
    Block
    VariableStatement
    EmptyStatement
    ExpressionStatement
    IfStatement
    IterationStatement
    ContinueStatement
    BreakStatement
    ReturnStatement
    WithStatement
    LabelledStatement
    SwitchStatement
    ThrowStatement
    TryStatement

Block :
    { StatementList_opt }

StatementList :
    Statement
    StatementList Statement

So the branches of an ifStatement may contain a block of statements (Block) or one of the other statements (other than Block). That means this is valid:

if (expr)
    someStatement;
else
    otherStatement;

And as StatementList may just contain a single statement, these examples are equivalent to the previous:

if (expr) {
    someStatement;
} else {
    otherStatement;
}

if (expr)
    someStatement;
else {
    otherStatement;
}

if (expr) {
    someStatement;
} else
    otherStatement;

And when we replace otherStatement by an additional IfStatement, we get this:

if (expr) {
    someStatement;
} else
    if (expr) {
        someOtherStatement;
    }

The rest is just code formatting:

if (expr) {
    someStatement;
} else if (expr) {
    someOtherStatement;
}