C#•5mo ago

Do while with int.TryParse - how?

I am trying to create a C-sharp program, that ask the user to pick a number between 1 and 3. It will then use that number to print one of three names I have in an array. This is how far I got:

string[] names = new string[] { "Peter", "John", "Paul" };

Console.Write("Select a number from 1-3: ");
string numberText = Console.ReadLine();

bool isValidNum = false;
int.TryParse(numberText, out int num)

do () {
    
} while (isValidNum == false);

string[] names = new string[] { "Peter", "John", "Paul" };

Console.Write("Select a number from 1-3: ");
string numberText = Console.ReadLine();

bool isValidNum = false;
int.TryParse(numberText, out int num)

do () {
    
} while (isValidNum == false);

I wanted the do-while to continue until the nubmerText is an actual number I can parse to Int, but also then be a valid number from 1-3 but I am kind of confused as to how to proceed.

21 Replies

mtreit•5mo ago

It's easier to use a while (true) loop and break when it's valid.

Unknown User•5mo ago

Message Not Public

Steadhaven•5mo ago

Aha. I learned that for things like this we use do-while, but perhaps I can juust use while and a break?

maxmahem•5mo ago

Even better might be to put it in its own function and return

Steadhaven•5mo ago

I didn't learn about functions yet (will later) so now I am trying to master while, do while, and the int try parse

mtreit•5mo ago

Something like this:

using System;

int val = 0;

while (true)
{
    Console.WriteLine("Enter a number from 1 to 3");
    var tmp = Console.ReadLine();

    if (!int.TryParse(tmp, out val) || (val < 1 || val > 3))
    {
        Console.WriteLine("Try again.");
        continue;
    }

    break;
}

Console.WriteLine($"You entered {val}");

using System;

int val = 0;

while (true)
{
    Console.WriteLine("Enter a number from 1 to 3");
    var tmp = Console.ReadLine();

    if (!int.TryParse(tmp, out val) || (val < 1 || val > 3))
    {
        Console.WriteLine("Try again.");
        continue;
    }

    break;
}

Console.WriteLine($"You entered {val}");

Steadhaven•5mo ago

(trying to learn step by step, but yeah I didn't say that sorry :p )

Steadhaven•5mo ago

I didn't see the var keyword before. Is it a mutable variable? (like var in javascript, instead of const)

Unknown User•5mo ago

Message Not Public

Steadhaven•5mo ago

Ok great, so its not unsafe :D

Unknown User•5mo ago

Message Not Public

Steadhaven•5mo ago

(other than mutablity, but I meant the scoping issues of var in JS)

Unknown User•5mo ago

Message Not Public

Steadhaven•5mo ago

Hm, so we don't have an equivalent of java final or javascript const to make something immutable? (or even Object.freeze in JS, or as const in typescript)

mtreit•5mo ago

const is a keyword in C#, as is readonly. Both can be used to enforce some level of immutability. const should generally be used only for things that are truly constant and guaranteed to never change (things like the value of pi for example) because otherwise if you change the constant value in a library, the consumer won't actually see the changed value unless they recompile their code.

if (!int.TryParse(tmp, out val) || val is < 1 or > 3)

if (!int.TryParse(tmp, out val) || val is < 1 or > 3)

Just realized you can use pattern matching to make the code a little nicer...

Steadhaven•5mo ago

thanks So readonly is how we can make something immutable in best practice

mtreit•5mo ago

Well, sort of. Like, if you make a property read only it means that property can't be mutated. But the thing the property references might be mutable. Like if you have a readonly property that points to an array, you can still mutate the array contents. Getting true immutability is (sometimes) a lot of work. A readonly field of a ReadOnlyCollection<T> for instance.

Steadhaven•5mo ago

I take it as I should just treat C# as a mutable OOP language :) I am just used to functional programming principles, but I guess I have to let it go for C#

mtreit•5mo ago

C# has a lot of nice support for functional programming approaches these days. I wouldn't necessarily treat it as just for OOP. (I dislike OOP and generally don't use things like inheritance hierarchies, for instance.)

Steadhaven•5mo ago

Ok thats great, I will probably learn about it in the future as I learn more

mtreit•5mo ago

LINQ for example has a pretty functional design.

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Do while with int.TryParse - how?