if Statement¶

The if statement decides whether to execute part of a script based on a condition, as in "if X, then do Y".

The syntax is as follows.

if(expression)
    statement or block
else
    statement or block

The first "statement or block" is executed when expression evaluates to true, and the second "statement or block" is executed when it evaluates to false. The else part can be omitted if it is not needed.

    if(a==b)
        inform("a and b are equal");

    if(a<b)
    {
        var t;
        t=a; a=b; b=t; // swap a and b
    }

    if(a==b)
        inform("a and b are equal");
    else
        inform("a and b are different");

Matching if and else¶

An else follows the rule "it pairs with the nearest preceding if that does not yet have an else".

For example, if you write

    if(expr) // ★
        if(expr) // ●
            statement;
        else // ●
            statement;
    else // ★
        statement;

the else marked ★ pairs with the if marked ★, and the else marked ● pairs with the if marked ●.

Be careful: in a free-form language like TJS2, even if you get the indentation wrong and write

    if(expr) // ★
        if(expr) // ●
            statement;
    else // ●
        statement;

the pairing is still as described above.

If you want to make the pairing explicit, enclose the inner part in a block, like this:

    if(expr) { // ★
        if(expr) // ●
            statement;
    }
    else // ★
        statement;