Why does a case statement NOT allow me to set variables that will be used inside a method

Question

Im trying to use a case statement to assign a value to a variable named "query". Depending on the value of a comboBox, the value of query will change. I assigned the "query" variable inside my method and want to use it within the method only. I get an error message that the "query" variable is unassigned even though it is being assigned at the top of the method. I have a work around but I dont know why this happens? any insight would be helpfull.

heres the code.

public void ExportKml()
    {
        string query;

            switch (txtTable.SelectedIndex)
            {
                case 0:
                    query = "Select * from dbo.HyacinthWaterBodyZones";
                    break;
                case 1:
                    query="Select * from lchcd.privateWatersFinal where waterbodypolygon is not null";
                    break;
                case 2:
                    query = "Select * from lchcd.publicWatersFinal where waterbodypolygon is not null";
                    break;

            }

            cs.Open();
            SqlCommand cmd = new SqlCommand(query, cs);   <<--Error Message 
            SqlDataReader polygon = cmd.ExecuteReader();
}

the "query" variable inside the line: SqlCommand cmd = new SqlComman(query,cs) gives an error stating it is unassigned local variable.

While your selected index may never *logically* be anything other than 0, 1, or 2, the compiler has no way of knowing this. You need to either initialize the variable with a dummy value, or add a `case else` that sets it to a dummy value. — jbabey, Sep 19 '13 at 15:46

Sam Leach · Accepted Answer · 2013-09-19T15:50:41.220

3

You need to asign an initial value to query. Either "" or string.Empty. You should include a default case in your switch also. See below:

public void ExportKml()
{
    string query = string.Empty;

    switch (txtTable.SelectedIndex)
    {
        case 0:
            query = "Select * from dbo.HyacinthWaterBodyZones";
            break;
        case 1:
            query = "Select * from lchcd.privateWatersFinal where waterbodypolygon is not null";
            break;
        case 2:
            query = "Select * from lchcd.publicWatersFinal where waterbodypolygon is not null";
            break;
        default:
            query = "";
            break;
    }

    // Add a check for empty string before trying the query.
    if(!string.IsNullOrWhiteSpace(query))
    {
        cs.Open();
        SqlCommand cmd = new SqlCommand(query, cs);
        SqlDataReader polygon = cmd.ExecuteReader();
    }
}

edited Sep 19 '13 at 15:50

answered Sep 19 '13 at 15:45

Sam Leach

12,746
9
45
73

The `default` case isn't needed, why **should** he include it anyways? – Philipp M Sep 19 '13 at 15:56
default case isnt needed but it was helpfull to know. Easy fix but it was giving me a headache – Nate S. Sep 19 '13 at 16:00
1

@CodeSlinger, read http://stackoverflow.com/questions/4649423/should-switch-statements-always-contain-a-default-clause – Sam Leach Sep 19 '13 at 16:05
@sam Leach, In my case the default isnt needed because the method does not run unless the user chooses an item in the combobox. Hence the case statment always returns a value from 0 to 2. Helpfull link though thanks! – Nate S. Sep 19 '13 at 16:11
Make sure you write some tests that prove your assumption. :) – Sam Leach Sep 19 '13 at 16:16

Steve · Answer 2 · 2013-09-19T15:52:12.743

3

Because the compiler has no way to know if your SelectedIndex will be always 0,1,or 2, so it gives you a strong suggestion to initialize the variable defined before the switch but used after it

string query = string.Empty;
switch(.....)
{
    ....
}
if(query.Length > 0)
{
    cs.Open();
    SqlCommand cmd = new SqlCommand(query, cs);   <<--Error Message 
    SqlDataReader polygon = cmd.ExecuteReader();    
}

Adding a default case to the switch statement works also, but, personally, I prefer to initialize the query variable before entering the switch statement. It is more clear to me and less prone to forgetting some other important initializations

edited Sep 19 '13 at 15:52

answered Sep 19 '13 at 15:46

Steve

213,761
22
232
286

Maybe use `string.IsNullOrWhiteSpace(query)` ? – Sam Leach Sep 19 '13 at 15:52
@SamLeach I am not sure, in this case it seems pointless because I already know that the string is not null and calling a method seems more expensive while a property should be faster. However these are just micro-optimizations. – Steve Sep 19 '13 at 15:59

score 2 · Answer 3 · answered Sep 19 '13 at 15:45

If the selected index is not 0-2, you will not hit any of the case statements. You need to include a default: case if you are going to assign a variable in the switch.

switch (txtTable.SelectedIndex)
{
    case 0:
        query = "Select * from dbo.HyacinthWaterBodyZones";
        break;
    case 1:
        query="Select * from lchcd.privateWatersFinal where waterbodypolygon is not null";
        break;
    case 2:
        query = "Select * from lchcd.publicWatersFinal where waterbodypolygon is not null";
        break;
    default:
        //assign query = something here
        break;
}

Why does a case statement NOT allow me to set variables that will be used inside a method

3 Answers3