What does "Use of unassigned local variable" mean?

I keep getting this error for annualRate, monthlyCharge, and lateFee.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Lab_5___Danny_Curro
{
    class Program
    {
        static void Main(string[] args)
        {
            string firstName;
            string lastName;
            int accNumber;
            string creditPlan;
            double balance;
            string status;
            Boolean late = false;
            double lateFee;
            double monthlyCharge;
            double annualRate;
            double netBalance;


            Console.Write("Enter First Name: ");
            firstName = Console.ReadLine();

            Console.Write("Enter Last Name: ");
            lastName = Console.ReadLine();

            Console.Write("Enter Account Number: ");
            accNumber = Convert.ToInt32(Console.ReadLine());


            Console.Write("Enter Credit Card Plan Number[Blank Will Enter Plan 0]: ");
            creditPlan = Console.ReadLine();

            Console.Write("Enter Balance: ");
            balance = Convert.ToDouble(Console.ReadLine());

            Console.Write("Is This Account Late?: ");
            status = Console.ReadLine().Trim().ToLower();

            if (creditPlan == "0")
            {
                annualRate = 0.35;  //35%
                lateFee = 0.0;
                monthlyCharge = balance * (annualRate * (1 / 12));
                return;
            }

            if (creditPlan == "1")
            {
                annualRate = 0.30;  //30%
                if (status == "y")
                {
                    late = true;
                }

                else if (status == "n")
                {
                    late = false;
                }
                if (late == true)
                {
                    lateFee = 25.00;
                }
                monthlyCharge = balance * (annualRate * (1 / 12));
                return;
            }
            if (creditPlan == "2")
            {
                annualRate = 0.20;  //20%
                if (status == "y")
                {
                    late = true;
                }

                else if (status == "n")
                {
                    late = false;
                }
                if (late == true)
                {
                    lateFee = 35.00;
                }
                if (balance > 100)
                {
                    monthlyCharge = balance * (annualRate * (1 / 12));
                }
                else
                {
                    monthlyCharge = 0;
                }
                return;
            }
            if (creditPlan == "3")
            {
                annualRate = 0.15;  //15%
                lateFee = 0.00;

                if (balance > 500)
                {
                    monthlyCharge = (balance - 500) * (annualRate * (1 / 12));
                }
                else
                {
                    monthlyCharge = 0;
                }
                return;
            }
            netBalance = balance - (lateFee + monthlyCharge);


            Console.WriteLine("Name: \t\t\t {0}  {1}", firstName, lastName);
            Console.WriteLine("Account Number: \t{0}", accNumber);
            Console.WriteLine("Credit Plane: \t\t{0}",creditPlan);
            Console.WriteLine("Account Late: \t\t{0}", late);
            Console.WriteLine("Balance: \t\t{0}", balance);
            Console.WriteLine("Late Fee: \t\t{0}", lateFee);
            Console.WriteLine("Interest Charge: \t{0}", monthlyCharge);
            Console.WriteLine("Net Balance: \t\t{0}",netBalance);
            Console.WriteLine("Annual Rate: \t\t{0}", annualRate);
            Console.ReadKey();
        }
    }
}

Solution 1:

The compiler isn't smart enough to know that at least one of your if blocks will be executed. Therefore, it doesn't see that variables like annualRate will be assigned no matter what. Here's how you can make the compiler understand:

if (creditPlan == "0")
{
    // ...
}
else if (creditPlan == "1")
{
    // ...
}
else if (creditPlan == "2")
{
    // ...
}
else
{
    // ...
}

The compiler knows that with an if/else block, one of the blocks is guaranteed to be executed, and therefore if you're assigning the variable in all of the blocks, it won't give the compiler error.

By the way, you can also use a switch statement instead of ifs to maybe make your code cleaner.

Solution 2:

Change your declarations to this:

double lateFee = 0.0;
double monthlyCharge = 0.0;
double annualRate = 0.0;

The error is caused because there is at least one path through your code where these variables end up not getting set to anything.

Solution 3:

Because if none of the if statements evaluate to true then the local variable will be unassigned. Throw an else statement in there and assign some values to those variables in case the if statements don't evaluate to true. Post back here if that doesn't make the error go away.

Your other option is to initialize the variables to some default value when you declare them at the beginning of your code.

Solution 4:

Give them a default value:

double lateFee=0.0;
double monthlyCharge = 0.0;
double annualRate = 0.0;

Basically, all possible paths don't initialize these variables.

Solution 5:

Use the keyword "default"!!!

    string myString = default;
    double myDouble = default;

    if(!String.IsNullOrEmpty(myString))
       myDouble = 1.5;

    return myDouble;