Variable declarations following if statements

Question

An issue came up on another forum and I knew how to fix it, but it revealed a feature of the compiler peculiar to me. The person was getting the error \"Embedded statement c

Answer 1

Adding the closing and opening braces on the else part of the if helped me like i have done below as opposed to what i was doing before adding them;

Before: this caused the error:

protected void btnAdd_Click(object sender, EventArgs e)
    {
        if (btnAdd.Text == "ADD")
        {

            CATEGORY cat = new CATEGORY
            {

                NAME = tbxCategory.Text.Trim(),
                TOTALSALEVALUE = tbxSaleValue.Text.Trim(),
                PROFIT = tbxProfit.Text.Trim()

            };
            dm.AddCategory(cat, tbxCategory.Text.Trim());
        }
        else
        // missing brackets - this was causing the error
            var c = getCategory();
            c.NAME = tbxCategory.Text.Trim();
            c.TOTALSALEVALUE = tbxSaleValue.Text.Trim();
            c.PROFIT = tbxProfit.Text.Trim();
            dm.UpdateCategory(c);

        btnSearchCat_Click(btnSearchCat, e);
    }

After: Added brackets in the else branch

protected void btnAdd_Click(object sender, EventArgs e)
    {
        if (btnAdd.Text == "ADD")
        {

            CATEGORY cat = new CATEGORY
            {

                NAME = tbxCategory.Text.Trim(),
                TOTALSALEVALUE = tbxSaleValue.Text.Trim(),
                PROFIT = tbxProfit.Text.Trim()

            };
            dm.AddCategory(cat, tbxCategory.Text.Trim());
        }
        else
        {
            var c = getCategory();
            c.NAME = tbxCategory.Text.Trim();
            c.TOTALSALEVALUE = tbxSaleValue.Text.Trim();
            c.PROFIT = tbxProfit.Text.Trim();
            dm.UpdateCategory(c);
        }
        btnSearchCat_Click(btnSearchCat, e);
    }

Answer 2

When you don't include the brackets, it executes the next line as if it were surrounded by brackets. Since it doesn't make much sense to declare a variable in that line (you wouldn't be able to use it ever), the C# compiler will not allow this to prevent you from accidentally doing it without knowing (which might introduce subtle bugs).

Here's part of Eric Lippert has to say about the C# compiler on this SO answer about name resolution:

...C# is not a "guess what the user meant" language...the compiler by design complains loudly if the best match is something that doesn't work

Answer 3

All compilers will allow you to compile code that is useless or of exceedingly low use. There are simply too many ways that a developer can use the language to create constructs with no use. Having the compiler catch all of them is simply too much effort and typically not worth it.

The second case is called out directly in the C# language specification at the start of section 8.0

The example results in a compile-time error because an if statement requires an embedded-statement rather than a statement for its if branch. If this code were permitted, then the variable i would be declared, but it could never be used. Note, however, that by placing i’s declaration in a block, the example is valid.

Example Code

void F(bool b) {
    if (b)
        int i = 44;
}

Answer 4

The C# language specification distinguishes between three types of statements (see chapter 8 for more details). In general you can have these statements:

• labeled-statement - my guess that this is for the old-fashioned goto statement
• declaration-statement - which would be a variable declaration
• embedded-statement - which includes pretty much all the remaining statements

In the if statement the body has to be embedded-statement, which explains why the first version of the code doesn't work. Here is the syntax of if from the specification (section 8.7.1):

if ( boolean-expression ) embedded-statement
if ( boolean-expression ) embedded-statement else embedded-statement

A variable declaration is declaration-statement, so it cannot appear in the body. If you enclose the declaration in brackets, you'll get a statement block, which is an embedded-statement (and so it can appear in that position).