This question already has answers here:
What does "Use of unassigned local variable" mean? [duplicate]
(11 answers)
Closed 3 years ago.
I am new to C#, my last programming language was C
I kept getting Use of unassigned local variable 'average'
The average it is pertaining was the average /= 10;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
int i, average;
int[] scores = new int[10];
Console.WriteLine("Enter 10 scores");
for (i = 0; i < 10; i++)
{
scores[i] = Convert.ToInt32(Console.ReadLine());
}
for (i = 0; i < 10; i++)
{
average = scores[i] + scores[i + 1];
i++;
}
average /= 10;
Console.WriteLine("Average of All the Scores: {0}", average);
Console.Read();
}
}
}
When you declare the variable 'average', set it to 0.
Here's a fixed version of your code, with comments as to why I made the change:
class Program
{
static void Main(string[] args)
{
//fix the 'use of undefined' error
int average = 0;
int[] scores = new int[10];
Console.WriteLine("Enter 10 scores");
//it's better to scope loop iteration variables to the loop unless you specifically need them outside
for (int i = 0; i < 10; i++)
{
scores[i] = Convert.ToInt32(Console.ReadLine());
}
for (int i = 0; i < 10; i++)
{
//your old code would crash here, and had the wrong algorithm for calculating an average; it didn't sum all the entered values, just the last two
average += scores[i];
}
average /= 10;
Console.WriteLine("Average of All the Scores: {0}", average);
Console.Read();
}
}
I was puzzled as to why the error occurred too because the second loop was clearly assigning a value and I knew that inner scopes could set values and the compiler would recognise them.. learning day for me too as I was formerly unaware that some loops are excluded even when they're set up so they look like they will definitely run. In simple terms it seems that when a loop is set up so that its running is conditional on a variable, the flow analysis considers that in some scenarios the loop might not run even though it's clear to the human reading the code that the loop will always run. Consider these:
//this is fine, flow analysis determines this loop will always run
int average;
while(true){
average = 0;
break;
}
average /= 10;
//this raises the same error even though we as a human can definitely see this loop will always run
int average;
int w = 0;
while(w<1){
average = 0;
}
average /= 10;
Making the loop conditional on a variable meant the compiler wa and longer sure the variable was assigned
As another more involved example, you could also fix your error with this bizarre construct as your first loop:
for (int i = 0; true; i++)
{
average = 0;
scores[i] = Convert.ToInt32(Console.ReadLine());
if(i >= 10)
break;
}
Again the compiler can be sure this loop will always run and your variable will be assigned
here's Peter's comment in case the other answer/the comment goes away:
the compiler doesn't implement any static flow analysis that would confirm that the average variable is set. According to the "definite assignment" rules of C#, loops are ignored because it's possible for a loop to not iterate even once. Thus, average is not definitely assigned, and thus the error. See marked duplicate, and of course the C# language specification, for more details.
Related
I am new to Kattis and trying solve the challenge Jumbo Javelin with C# but I get run time error even though I am exiting my program with 0.
Here is my code:
using System;
namespace JumboJavelin
{
class Program
{
static void Main(string[] args)
{
int l = int.Parse(Console.ReadLine());
int sum = 0;
int loss = 1;
for (int n = 0; n <= 100; n++)
{
sum += l;
if((n + 1) % 2 == 0 && !n.Equals(0))
{
sum -= ((n + 1) / 2)*loss;
}
try
{
l = int.Parse(Console.ReadLine());
}
catch (FormatException)
{
break;
}
}
Console.WriteLine(sum);
Environment.Exit(0);
}
}
}
Can someone please help me? I know my solution eventually outputs the wrong answer but right now I am trying to get rid of the run time error since it works perfectly fine on Visual Studio 2019.
All help is appreciated. Thanks
If you change the error your catch to Exception you will see that it is actually a wrong answer, so something goes wrong. You do exit your program with an exit code 0 at the bottom of your code, however, it throws an Exception somewhere else. Two things to consider:
First, the problem statement explains that as a first input, you get an integer N (this N indicates the amount of steel rods he has) and CAN BE between 1 and 100 (1 not inclusive hence, 1<N<=100). You now have a loop that always loops from 1 to 100. And the loop should loop from 1 up to and including whatever value N is. Try to see what you can do about that.
Second you read the input at the "tail" of the loop. This means that after the last cycle you do another read input. And that you do not read the first l. Try changing reading the input for l at the beginning of the loop. (and the first input you read in your Main, should not be for l (see point 1)).
See how far this gets you, is something is not clear please let me know.
As Kasper pointed out, n is dynamically provided on the first line; don't assume you have 100 lines to collect with for (int n = 0; n <= 100; n++).
There's no need to handle errors with the format; Kattis will always adhere to the format they specify. If something goes wrong parsing their input, there's no point trying to catch it; it's up to you to fix the misunderstanding. It's better to crash instead of catch so that you won't be fooled by Kattis telling you the failure was due to a wrong answer.
A simple approach is as follows:
Collect n from the first line of input; this is the preamble
Loop from 0 to n, collecting each line
Accumulate the values per line into a sum
Print sum - n + 1, the formula you can derive from their samples
using System;
class JumboJavelin
{
static void Main(string[] args)
{
int n = int.Parse(Console.ReadLine());
int sum = 0;
for (int i = 0; i < n; i++)
{
sum += int.Parse(Console.ReadLine());
}
Console.WriteLine(sum - n + 1);
}
}
You can use this pattern on other problems. You won't always aggregate one result after n lines of input though; sometimes the input is a single line or you have to print something per test case. Some problems require you to split and parse each line on a delimiter.
Regardless of the case, focus on gathering input cleanly as a separate step from solving the problem; only combine the two if you're confident you can do it without confusion or if your solution is exceeding the time limit and you're sure it's correct otherwise.
This question already has answers here:
What is the difference between i++ and ++i?
(7 answers)
Closed 3 years ago.
I dont understand why the value of i and k is still 5 in line number 19 ,20,after post increment?
The value of i is still 5 though after post increment.
`using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
namespace Increment
{
class Program
{
static void Main(string[] args)
{
int i = 5;
int j = 10;
Console.WriteLine("before incrementing{0}",i);
i=i++;
Console.WriteLine("after incrementing {0}",i); //i=5?
int k = i;
Console.WriteLine("after incrementing i and assign {0}", k);//K=5?
}
}
}`
Imagine post-increment and pre-increment as functions:
int PreIncrement(ref int i)
{
i = i + 1;
return i;
}
int PostIncrement(ref int i)
{
int valueBefore = i;
i = i + 1;
return valueBefore;
}
In this case
i = i++;
would be the equivalent of
i = PostIncrement(ref i);
You are performing two actions, in this order:
Incrementing i
Setting i to equal the value it equalled before it was incremented
The documentation for ++ has reasonably clear examples. "The result of x++ is the value of x before the operation, as the following example shows... ."
That means however you use x++ in an expression you will be getting the initial value, i.e. prior to x being incremented. So if x is 4 then the value 4 will be used in the expression and x will be incremented to 5. If the expression's value is assigned to a variable then the variable is set to 4. You happen to have chosen x as the target of the assignment, thus overwriting the post-incremented value.
The problem asks for 1000 iteration of the code.It must allow for whole numbers from 0-100000 and show how many odd numbers were generated during the iterations then show the highest number and lowest numbers generated. The first part of my code works and shows how many odd numbers were generated however I can not figure out how to capture/edit the smallest and largest numbers that were generated while the code was running.
I have tried many different methods including while loops and my if, else if, conditions. I have placed them through out my program however I am stuck. I know the problem is with the randNum going into the variables and staying there through each iterations without going back to zero.(when I run my code it displays zero for the smallNum and LargeNum.)
here is my work so far
using System;
using System.Windows.Forms;
namespace BissonnetteMessageBox
{
class Program
{
static void Main(string[] args)
{
int oddNumCount = 0;
int smallNum = 0;
int largeNum = 0;
Random randNum = new Random();
for (int i = 0; i < 1000; i++)
{
int num = randNum.Next(100000);
int remain = num % 2;
if (remain != 0)
{
oddNumCount++;
}
if (num < smallNum)
{
num = smallNum;
}
else if (num > largeNum)
{
num = largeNum;
}
}
MessageBox.Show("the Number of odd numbers generated: " + oddNumCount +
"\nSmallest number was: " + smallNum +
"\nLargerst number was: "+ largeNum , "random number generation results");
}
}
}
Here is what the result is when I run my program:
The lines "num = smallNum;" and "num = largeNum;" are wrong. They should be "smallNum = num;" and "largeNum = num;". That's because the variable (or constant, expression) on the right side of the "=" overwrites the variable on the left side. It's not like in the mathematics, where it can be turned around.
Here is the right code:
using System;
using System.Windows.Forms;
namespace BissonnetteMessageBox
{
internal class Program
{
private static void Main(string[] args)
{
int oddNumCount = 0;
int smallNum = 0;
int largeNum = 0;
Random randNum = new Random();
for (int i = 0; i < 1000; i++)
{
int num = randNum.Next(100000);
int remain = num % 2;
if (remain != 0)
{
oddNumCount++;
}
if (num < smallNum)
{
smallNum = num;
}
else if (num > largeNum)
{
largeNum = num;
}
}
MessageBox.Show("the Number of odd numbers generated: " + oddNumCount +
"\nSmallest number was: " + smallNum +
"\nLargerst number was: " + largeNum, "random number generation results");
}
}
}
A number of people have pointed out the two main issues with the code itself.
I'd like to talk about how to approach issues like this going forward as you learn how to program.
It looks like you're in Visual Studio, programming in C#. Well, the great news is, Visual Studio makes it really really easy to see what's going on as you step through your program. You can set a breakpoint in your code, so that when the program reaches that line, it stops - highlighting the line and letting you see what's going on. From there, you can step forward lines of code, watching as values change.
Here are some helpful places to get started:
Using breakpoints in Visual Studio
Tips and tricks with the VS debugger
Some more tips and tricks with debugging
This will be incredibly valuable going forward. Because, to be honest, you're not going to like programming very much if you find yourself having to post questions online whenever you run into any sort of snag. Being able to figure out the snags will make your life far more enjoyable :-)
I have been practicing c# nowadays and decided to write a code that converts any decimal to any base representation for practice purpose. And i have some troubles. Since i want to practice i decided to do it with an additional function where calculations take place. First i wanted to use an array to keep my result. But since ,at the beginning, i do not know the length of the array i could not define it.So i decided to use list(somehow i assumed undeclared slots are 0 as default). This is what i end up with.
class MainClass
{
static double number;
static double baseToConvert;
static int counter = 0;
static List<double> converted = new List<double>();
public static void Main(string[] args)
{
Console.WriteLine("Enter a decimal");
number = double.Parse(Console.ReadLine());
Console.WriteLine("Enter a base you want to convert to");
baseToConvert = double.Parse(Console.ReadLine());
ConverterToBase(number);
for (int i = converted.Count - 1; i >= 0; i--)
{
Console.WriteLine(converted[i]);
}
Console.ReadLine();
}
public static void ConverterToBase(double x)
{
double temp = x;
while (x >= baseToConvert)
{
x /= baseToConvert;
counter++;
}
converted[counter] = x;
counter = 0;
if (temp - x * Math.Pow(baseToConvert, Convert.ToDouble(counter)) >= baseToConvert)
{
ConverterToBase(temp - x * Math.Pow(baseToConvert, Convert.ToDouble(counter)));
}
else
{
converted[0] = temp - x * Math.Pow(baseToConvert, Convert.ToDouble(counter));
}
}
}
But after i write inputs console gets stuck without an error. My guess is that since i do not have any elements in the list " converted[counter] " does not make sense. But i do not know maybe the problem is somewhere else.
My question is not about the way i calculate the problem(Of course any suggestions are welcomed). I just want to know what i am doing wrong and how i can handle such situation(unknown array size , use of list , accessing a variable,array,.. etc from another method... ).
Thanks.
My previous answer was wrong as pointed out by #Rufus L. There is no infinite for loop. However upon further review, there seems to be an infinite recursion going on in your code in this line:
if (temp - x * Math.Pow(baseToConvert, Convert.ToDouble(counter)) >= baseToConvert)
{
ConverterToBase(temp - x * Math.Pow(baseToConvert, Convert.ToDouble(counter)));
}
ConverterToBase calls itself and there seems to be no base case nor return statement to end the recursion.
In the method named "ConverterToBase(double x)" you want to set value of 0 element. But you didn't add any element. The converted is Empty.
Firstly add value or values to your list.
I have a simple c# console application but i am getting wrong output why?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication11
{
class Program
{
static void Main(string[] args)
{
int i = 100;
for (int n = 0; n < 100; n++)
{
i = i++;
}
Console.WriteLine(i);
}
}
}
i++ is an expression which returns i, then increments it.
Therefore, i = i++ will evaluate i, increment i, then assign i to the original value, before it was incremented.
You need to use ++i, which will return the incremented value.
I'm guessing that you really want an explanation as to why it doesn't work as expected, rather than to actually get the result since you can get that by setting i equal to 200 in the first place.
The postincrement operator is applied after a temporary copy of the variable is created. The temporary is used for operations in the statement then the assignment is performed, thus your loop is equivalent to:
for (int n = 0; n < 100; n++)
{
j = i;
i++;
i = j;
}
Since that's the case, the increment is basically discarded and i is never actually incremented.
i = i++;
This sets i to the old value of i, then increments it. I think you want:
i++;
Or better yet if your compiler is lame and doesn't optimize the return:
++i;
Cheers.
The line i = i++; writes twice to the variable i. The post increment is executed first, but then the assignment statement overwrites it.
Try just i++;
Just use i++, not i = i++.