C#•16mo ago

Making my FIRST very basic calculator (don't judge), need help and clarification

Hiya, I've followed a couple of Microsoft's tutorials on integers and strings, I've decided to try my best and make a very basic calculator program to perform operations on two numbers, a and b. I'm having problems with my code as I keep getting errors such as "unassigned local variable". I don't really understand the whole local business and what not, could someone perhaps help me by explaining it to me like I'm an idiot? Here's a bit of code I wrote so far, now I'm working on selecting the operation.

44 Replies

ineffableOP•16mo ago

using System;

Console.WriteLine("VERY Simple Calculator v1.0 \nMade by Lucas Tumors (TM)\n");
Console.WriteLine("\nList of available operations:\n(a + b) - adds two numbers together\n(a - b) - subtracts one number from another\n(a * b) - multiplies two numbers together\n(a / b) - divides one number by another\n");

int a;
int b;

Console.WriteLine("\nChoose the first number:");

bool valid1 = false;
while (valid1 == false)
{
    var stringNumber1 = Console.ReadLine();
    int numericValue1;
    bool isNumber1 = int.TryParse(stringNumber1, out numericValue1);

    if (isNumber1 != true)
    {
        Console.WriteLine("You need to choose a valid number");
    }
    else
    {
        
         a = numericValue1;
        valid1 = true;
    }
}

Console.WriteLine("\nChoose the second number:");

bool valid2 = false;
while (valid2 == false)
{
    var stringNumber2 = Console.ReadLine();
    int numericValue2;
    bool isNumber2 = int.TryParse(stringNumber2, out numericValue2);

    if (isNumber2 != true)
    {
        Console.WriteLine("You need to choose a valid number");
    }
    else
    {
        b = numericValue2;
        valid2 = true;
    }

}

Console.WriteLine("\nChoose a mathematical operation:\n1. Addition (+)\n2. Subtraction (-)\n3. Multiplication (*)\n4. Division (/)");

bool valid3 = false;
while (valid3 == false)
{
    var stringNumber3 = Console.ReadLine();
    int numericValue3;
    bool isNumber3 = int.TryParse(stringNumber3, out numericValue3);


    if (isNumber3 != true || numericValue3 < 1 || numericValue3 > 4)
    {
        Console.WriteLine("You need to choose a valid option");
    }
    else if (isNumber3 == true && numericValue3 == 1)
    {
        int c = a + b;
        Console.WriteLine("$The sum of the two equals {c}");
    }
}

using System;

Console.WriteLine("VERY Simple Calculator v1.0 \nMade by Lucas Tumors (TM)\n");
Console.WriteLine("\nList of available operations:\n(a + b) - adds two numbers together\n(a - b) - subtracts one number from another\n(a * b) - multiplies two numbers together\n(a / b) - divides one number by another\n");

int a;
int b;

Console.WriteLine("\nChoose the first number:");

bool valid1 = false;
while (valid1 == false)
{
    var stringNumber1 = Console.ReadLine();
    int numericValue1;
    bool isNumber1 = int.TryParse(stringNumber1, out numericValue1);

    if (isNumber1 != true)
    {
        Console.WriteLine("You need to choose a valid number");
    }
    else
    {
        
         a = numericValue1;
        valid1 = true;
    }
}

Console.WriteLine("\nChoose the second number:");

bool valid2 = false;
while (valid2 == false)
{
    var stringNumber2 = Console.ReadLine();
    int numericValue2;
    bool isNumber2 = int.TryParse(stringNumber2, out numericValue2);

    if (isNumber2 != true)
    {
        Console.WriteLine("You need to choose a valid number");
    }
    else
    {
        b = numericValue2;
        valid2 = true;
    }

}

Console.WriteLine("\nChoose a mathematical operation:\n1. Addition (+)\n2. Subtraction (-)\n3. Multiplication (*)\n4. Division (/)");

bool valid3 = false;
while (valid3 == false)
{
    var stringNumber3 = Console.ReadLine();
    int numericValue3;
    bool isNumber3 = int.TryParse(stringNumber3, out numericValue3);


    if (isNumber3 != true || numericValue3 < 1 || numericValue3 > 4)
    {
        Console.WriteLine("You need to choose a valid option");
    }
    else if (isNumber3 == true && numericValue3 == 1)
    {
        int c = a + b;
        Console.WriteLine("$The sum of the two equals {c}");
    }
}

And I guess I should have commented to clarify what I'm trying to do, but I figured it's so basic that it didn't need this. Essentially: 1. The program welcomes the user and displays a message asking for the first number (a) 2. The program checks whether their input is an actual number, if not it repeats the question, if yes it assigns the number to "a" 3. The program does the same thing but for a "b" 4. When it has the two numbers and they're indeed numbers, it asks for one of the four math operations I've included 5. The program checks whether the user inputed a number between 1-4, which correspond to the math operation

Jimmacle•16mo ago

what errors do you currently have?

ineffableOP•16mo ago

CS0165: use of unassigned local variables "a" and "b" just by the 4th line from the end I guess it has to do something with variables not being accessible even though they exist in the code?

hiyosilver•16mo ago

It's telling you that a and b don't have defined values by the time that line executes. The compiler doesn't like it if there is a chance of the variable being uninitialized when it's used. A simple fix would be to just give them a default value, or to make sure than whatever branch of your program executes, a and b are always set to some definite value.

hiyosilver•16mo ago

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-messages/cs0165

Compiler Error CS0165

ineffableOP•16mo ago

so at the beginning of the code I could do:

int a = 0
int b = 0

int a = 0
int b = 0

and it would assign them SOME value?

hiyosilver•16mo ago

Specifically 0, yes 🙂 That should do it.

ineffableOP•16mo ago

Okay, let me try then!

hiyosilver•16mo ago

I don't know if you want to keep it separate for redability, but you could simplify this kind of thing

var stringNumber3 = Console.ReadLine();
    int numericValue3;
    bool isNumber3 = int.TryParse(stringNumber3, out numericValue3);

if (isNumber3 != true || numericValue3 < 1 || numericValue3 > 4)
{
    Console.WriteLine("You need to choose a valid option");
}

var stringNumber3 = Console.ReadLine();
    int numericValue3;
    bool isNumber3 = int.TryParse(stringNumber3, out numericValue3);

if (isNumber3 != true || numericValue3 < 1 || numericValue3 > 4)
{
    Console.WriteLine("You need to choose a valid option");
}

if(int.TryParse(Console.ReadLine(), out int numericValue ||
   numericValue < 1 ||
   numericValue > 4) {
  ...
}

if(int.TryParse(Console.ReadLine(), out int numericValue ||
   numericValue < 1 ||
   numericValue > 4) {
  ...
}

If you want to keep the string and int variables, I would at least use the result of TryParse directly as the condition. Just avoids an (imo) unnecessary extra step. Also, the expression isNumber != true returns a bool, but isNumber is already a bool, so you don't need the extra comparison. You can use its value directly like isNumber or !isNumber

ineffableOP•16mo ago

oh yeah, why assign

Console.ReadLine()

Console.ReadLine()

into a separate variable when I can just use the outputs of the

Console.ReadLine()

Console.ReadLine()

directly in the

int.TryParse()

int.TryParse()

, is this what you mean?

hiyosilver•16mo ago

Yes.

ineffableOP•16mo ago

Didn't know you could do that!

hiyosilver•16mo ago

You could argue that maybe stuffing it all in one line might make it less readable for some. You don't have to do it that way, and if you find your approcah clearer, thats perfectly fine too 🙂

ineffableOP•16mo ago

Definitely, I'm just doing it the very crude way just to get it working 😄

hiyosilver•16mo ago

That's the nice thing about naming bools stuff like isX or canY etc. You can use them directly a bit like regular speech, rather than having to do these abstract math-y operations on them.

ineffableOP•16mo ago

So it's a good practice to name booleans like this? I thought it'd get confusing with the booleans which are already in-built

hiyosilver•16mo ago

Can you give an example? Someone else might correct me, but I would say generally it is. Bools express something about your program that either is or isn't the case. Naming them this way is just quite natural and easy to read and reason about. Is this valid? Is this thing active? Can I do this operation? Anything built-in using this naming scheme is probably named like that for a reason.

ineffableOP•16mo ago

Well the example is "isNumber". But I get what you mean! Well I think everything is working now, my mini very crude calculator is working!

hiyosilver•16mo ago

Yeah, that's the example here. Although try to image what you would call this bool if you didn't want to use that naming scheme. What name could you use that wouldnt be confusing?

ineffableOP•16mo ago

Well, except the division result showing only the whole number and not fractional part...

hiyosilver•16mo ago

Ah yes That's another thing

ineffableOP•16mo ago

I dunno, I think it's named pretty nicely

hiyosilver•16mo ago

It is 🙂 That#s what I'm saying

ineffableOP•16mo ago

else if (isNumber3 == true && numericValue3 == 4)
{
    double c = a / b;
    Console.WriteLine($"The result of division of the two equals {c}.");
    valid3 = true;
}

else if (isNumber3 == true && numericValue3 == 4)
{
    double c = a / b;
    Console.WriteLine($"The result of division of the two equals {c}.");
    valid3 = true;
}

I made the "c" a double, is that correct?

hiyosilver•16mo ago

Kind of

ineffableOP•16mo ago

Also holy cow you're of such help you've no idea

hiyosilver•16mo ago

The problem here is a little thing called integer division integers dont behave the way you would expect from "normal" math as you might be thinking about it. Integers have no fractional part They can only be whole numbers So while c is a double, which would be correct, a and b are integers. The result of an operation of only ints can only ever be another int. So by the time you assign the result (which is an int) to you double, any fractional part that should be there is already gone

ineffableOP•16mo ago

So I need to make all the variables into doubles?

hiyosilver•16mo ago

Well, no not necessarily You could but to keep it simple, you could just cast one of your inputs to a double for example. You only need one of them to be a double, for the operation to no longer be integer division, but dividing with fractional parts like you would expect. e.g. double c = (double)a / b; should do the trick.

ineffableOP•16mo ago

IT WORKS :D!!! I am so happy even though I made only this

hiyosilver•16mo ago

5 / 2 returns 2 because ints 5.0 / 2 returns 2.5 because one of them is a double 🙂

ineffableOP•16mo ago

I also noticed that even though I changed "a" and "b" into doubles, "c" produced errors because it was an int in some other line

hiyosilver•16mo ago

Everyone needs to start somewhere, no need to put yourself down 😉 Ah yes, you can't re-declare a different variable with a name you've already used.

ineffableOP•16mo ago

I am so happy Now I want to export this so I can show to my friends who dont have Visual Studio I suppose it's under "build" tab?

hiyosilver•16mo ago

What editor/ide are you using? Although honestly I won't know much whichever one it is 😄

ineffableOP•16mo ago

Visual Studio 2022

hiyosilver•16mo ago

There should be a drop down just under Build That is probably set to Debug, which is how you've been testing your program I assume.

ineffableOP•16mo ago

Ooo I see And I need to "release" it?

hiyosilver•16mo ago

If you set it to release and Build your project again, it should do it automatically The default should be a bin folder in your project directory.

ineffableOP•16mo ago

I SEE IT Man i am beyond happy Thank yo uso much you're a godsend Can I message you privately on discord with some more help if I need it later?

hiyosilver•16mo ago

Sure. No guarantees that I will have any idea but I can try. Man I'm typing like I'm drunk today, I keep missing whole words.

Jimmacle•16mo ago

it's best to make new help posts here so anyone can chime in (or keep using the same one if it's the same problem)

hiyosilver•16mo ago

^this actually, I don't mind helping, but on balance I probably know less than average. You'd be missing out on many people here way more knowledgable than me and I would not be corrected if tell you something that's just plain wrong. @ineffable_

ineffableOP•16mo ago

Yeah, makes sense.

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Making my FIRST very basic calculator (don't judge), need help and clarification