C#•2y ago

❔ ✅ Inputing numbers

I want to write a short code that gets random input. It reads two numbers between random inputs.

using System;
namespace hello_wolrd;
class Program
{
    static void Main(string[] args)
    {

        int a = Inputer.ReadSymbol();
        int b = Inputer.ReadSymbol();
        Console.WriteLine(a + b);
    }
}

class Inputer
{
    public static int ReadSymbol()
    {
        int symbol = Console.Read();
        while ((symbol < '0') || (symbol > 9))
            symbol = Console.Read();
        int x = 0;

        while ((symbol >= '0') && (symbol <= '9'))
        {
            x = 10 * x + (symbol - '0');
            symbol = Console.Read();
        }


        return x;
    }
}

using System;
namespace hello_wolrd;
class Program
{
    static void Main(string[] args)
    {

        int a = Inputer.ReadSymbol();
        int b = Inputer.ReadSymbol();
        Console.WriteLine(a + b);
    }
}

class Inputer
{
    public static int ReadSymbol()
    {
        int symbol = Console.Read();
        while ((symbol < '0') || (symbol > 9))
            symbol = Console.Read();
        int x = 0;

        while ((symbol >= '0') && (symbol <= '9'))
        {
            x = 10 * x + (symbol - '0');
            symbol = Console.Read();
        }


        return x;
    }
}

im somewhere around here.. but i havent figured the minus numbers also... the input can be something like:

115
aaa-12

a

115
aaa-12

a

22 Replies

Angius•2y ago

Use int.TryParse() if you want to support negative numbers

Spekulant•2y ago

could you explain more this is my first code in c#... i come from python xd also new to C languages

Angius•2y ago

$tryparse

MODiX•2y ago

The TryParse pattern is considered best practice of parsing data from a string: - a TryParse method returns true or false to inform you if it succeeded or not, so you can use it directly in a condition, - since C# 7 you can declare a variable that will be used as an out argument inline in an argument list, - it forces you to check if the out argument contains valid data afterwards, Avoid: Convert.ToInt32 — it's a bad choice for parsing an int. It exists only for backwards compatibility reasons and should be considered last resort.

return Convert.ToInt32(null); //returns 0. null should not be considered as 0 ever
return Convert.ToInt32("asdf"); //throws FormatException

return Convert.ToInt32(null); //returns 0. null should not be considered as 0 ever
return Convert.ToInt32("asdf"); //throws FormatException

(Note: Convert does contain useful conversion methods: To/FromBase64String, To/FromHexString, ToString(X value, int toBase), ToX(string? value, int fromBase)) Avoid: int.Parse — you have to use a try/catch statement to handle invalid input, which is a less clean solution.

var number = int.Parse("abc"); //throws FormatException
var number = int.Parse(""); //throws FormatException

var number = int.Parse("abc"); //throws FormatException
var number = int.Parse(""); //throws FormatException

Use int.TryParse https://docs.microsoft.com/en-us/dotnet/api/system.int32.tryparse?view=net-5.0#System_Int32_TryParse_System_String_System_Int32__

if (int.TryParse(someInput, out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

if (int.TryParse(someInput, out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

Int32.TryParse Method (System)

Converts the string representation of a number to its 32-bit signed integer equivalent. A return value indicates whether the operation succeeded.

Spekulant•2y ago

@Angius i though i should have another variable that checks if its minus sign and if the following chars are number then its negative would int.TryParse() work even on a str like: ag-123gago

Angius•2y ago

MODiX•2y ago

Angius#1586

REPL Result: Success

if (int.TryParse("ag-123gago", out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

if (int.TryParse("ag-123gago", out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

Console Output

You didn't give me a valid number :c

You didn't give me a valid number :c

Compile: 610.725ms | Execution: 87.333ms | React with ❌ to remove this embed.

Spekulant•2y ago

well i want my code to spit out -123 so should i still use int.TryParse

Angius•2y ago

Ah, you want to pull out numbers from random gibberish? As in, you want usyadgfuyawi4rdsfjhg to give you 4?

Spekulant•2y ago

yes i want to pull out 2 numbers from gibberish and sum them up but they can be like negative so i have to check if there is a minus sign before the number began

Angius•2y ago

You could just try regex Or, sure, build some sort of a parser

var numbers = new List<int>();
var queue = new Queue(input);
while (queue.Count > 0)
{
    var ch = queue.Dequeue();
    if (ch.IsNumber)
    {
        numbers.Add(ch - '0');
    }
    else if (ch == '-')
    {
        var num = ch.Dequeue();
        if (num.IsNumber)
        {
            numbers.Add((num - '0') * -1);
        }
    }
}

var numbers = new List<int>();
var queue = new Queue(input);
while (queue.Count > 0)
{
    var ch = queue.Dequeue();
    if (ch.IsNumber)
    {
        numbers.Add(ch - '0');
    }
    else if (ch == '-')
    {
        var num = ch.Dequeue();
        if (num.IsNumber)
        {
            numbers.Add((num - '0') * -1);
        }
    }
}

something like that

Spekulant•2y ago

dont know what regex is

Angius•2y ago

Regular expressions https://learn.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.regex?view=net-7.0 https://regex101.com/

Spekulant•2y ago

using System;
namespace hello_wolrd;

class Inputer
{
    public static int ReadSymbol()
    {
        int symbol = Console.Read();
        int checker = '?';
        while ((symbol < '0') || (symbol > '9'))
            checker = symbol;
            symbol = Console.Read();
            
        int x = 0;

        while ((symbol >= '0') && (symbol <= '9'))
        {
            x = 10 * x + (symbol - '0');
            symbol = Console.Read();
        }
        if (checker == '-')
            x = -x;

        return x;
    }
}

class Program
{
    static void Main(string[] args)
    {

        int a = Inputer.ReadSymbol();
        int b = Inputer.ReadSymbol();
        Console.WriteLine(a + b);
    }
}

using System;
namespace hello_wolrd;

class Inputer
{
    public static int ReadSymbol()
    {
        int symbol = Console.Read();
        int checker = '?';
        while ((symbol < '0') || (symbol > '9'))
            checker = symbol;
            symbol = Console.Read();
            
        int x = 0;

        while ((symbol >= '0') && (symbol <= '9'))
        {
            x = 10 * x + (symbol - '0');
            symbol = Console.Read();
        }
        if (checker == '-')
            x = -x;

        return x;
    }
}

class Program
{
    static void Main(string[] args)
    {

        int a = Inputer.ReadSymbol();
        int b = Inputer.ReadSymbol();
        Console.WriteLine(a + b);
    }
}

i got this but when i input 1 and 2 in terminal it prints out 0

Angius•2y ago

Remember that it's not Python What you have here is

while ((symbol < '0') || (symbol > '9'))
{
    checker = symbol;
}
symbol = Console.Read();

while ((symbol < '0') || (symbol > '9'))
{
    checker = symbol;
}
symbol = Console.Read();

not

while ((symbol < '0') || (symbol > '9'))
{
    checker = symbol;
    symbol = Console.Read();
}

while ((symbol < '0') || (symbol > '9'))
{
    checker = symbol;
    symbol = Console.Read();
}

Spekulant•2y ago

okey thanks it works now can it be written more elegantly tho like the same thing but so much better and cleaner?like programs in python @Angius also if i have only integers also negative on input and i want to put it inside an array should i use the code that you pasted the regex one?

Angius•2y ago

You can use regex, sure

Spekulant•2y ago

dont know why you use queue tho

Angius•2y ago

To make parsing easier Also, the code there is not regex

Spekulant•2y ago

c# harder then cpp !close

Accord•2y ago

Closed! Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ ✅ Inputing numbers