Use of unassigned local variable that is assigned

Question

The below code runs a 'for' loop to create months 1 through 12 then names each month Jan through Dec according to their number. That pieces compiles fine. At the bottom where I try to write the month name on the screen is where it is failing. It says "use of unassigned local variable 'monthName'; however monthName was just used previously and is declared above. Any help you could provide would be greatly appreciated.

for (int month = 1; month <= 12; month++)
{
    string monthName;
    double monthlyProd = .1 * dProdRate;
    double monthlySales = .07 * dSalesRate;
    if (month == 1) { monthName = "Jan"; }
    if (month == 2) { monthName = "Feb"; monthlyProd = 0; }
    if (month == 3) { monthName = "Mar"; }
    if (month == 4) { monthName = "Apr"; }
    if (month == 5) { monthName = "May"; }
    if (month == 6) { monthName = "Jun"; monthlyProd = 0; }
    if (month == 7) { monthName = "Jul"; }
    if (month == 8) { monthName = "Aug"; }
    if (month == 9) { monthName = "Sep"; monthlySales = (.15 * dSalesRate); }
    if (month == 10) { monthName = "Oct"; }
    if (month == 11) { monthName = "Nov"; }
    if (month == 22) { monthName = "Dec"; monthlySales = (.15 * dSalesRate); }
}
dEndingInventory += dPreviousProd - dPreviousSales;
Console.WriteLine("{0}{1,15}{2,15}{3,15}", monthName, monthlyProd, monthlySales, dEndingInventory);

Answer 1

You know that month can only take the values 1 to 12 inclusive but the compiler is not that smart. If say month is 0 then the variable monthName is never assigned a value and that is what the compiler is complaining about. To fix it simply initialize the variable when you declare it:

string monthName = null;

Also, there is something fishy about your code because monthName is used outside the loop where it is declared but I assume that this is a typo because the code as it stands now will not give you the error you are asking about.

Answer 2

You have declared the monthName, monthlyProd,monthlySales under the scope of For Loop and trying to use those variables out of the scope of For Loop. You should declare variables before for loop-

string monthName;
double monthlyProd = .1 * dProdRate;
double monthlySales = .07 * dSalesRate;

for (int month = 1; month <= 12; month++)
{

    if (month == 1) { monthName = "Jan"; }
    if (month == 2) { monthName = "Feb"; monthlyProd = 0; }
    if (month == 3) { monthName = "Mar"; }
    if (month == 4) { monthName = "Apr"; }
    if (month == 5) { monthName = "May"; }
    if (month == 6) { monthName = "Jun"; monthlyProd = 0; }
    if (month == 7) { monthName = "Jul"; }
    if (month == 8) { monthName = "Aug"; }
    if (month == 9) { monthName = "Sep"; monthlySales = (.15 * dSalesRate); }
    if (month == 10) { monthName = "Oct"; }
    if (month == 11) { monthName = "Nov"; }
    if (month == 22) { monthName = "Dec"; monthlySales = (.15 * dSalesRate); }
}
dEndingInventory += dPreviousProd - dPreviousSales;
Console.WriteLine("{0}{1,15}{2,15}{3,15}", monthName, monthlyProd, monthlySales, dEndingInventory);