Banknotes and coins C#

Question

I’m having an error in an algorithm I’m implementing in the c# language on the JUDGE website online, Banknotes and coins And I don’t really know what it is, but I believe it’s about the calculations, it gives a rounding error, I realized this by putting several writeln, after the calculation, just to keep up with the variations, with some inputs works perfectly. only does not work with this entry 576.43 and others. it works all right, but the last line of data output gives 2 1c coins, being that are 3 coins.. I don’t know how to explain it, but I hope you understand my logic

using System;

class MainClass {
  public static void Main (string[] args) {
    double n1,n2,n3,n4,n5,n6,m1,m2,m3,m4,m5,m6;
    double a = double.Parse(Console.ReadLine());

    n1 = (a - a % 100)/100;
    a = a % 100;

    n2 = (a - a % 50)/50;
    a = a % 50;

    n3 = (a - a % 20)/20;
    a = a % 20;

    n4 = (a - a % 10)/10;
    a = a % 10;

    n5 = (a - a % 5)/5;
    a = a % 5;

    n6 = (a - a % 2)/2;
    a = a % 2;

    m1 = (a - a % 1)/1;
    a = a % 1;

    m2 = (a - a % 0.50)/0.50;
    a = a % 0.50;

    m3 = (a - a % 0.25)/0.25;
    a = a % 0.25;

    m4 = (a - a % 0.10)/0.10;
    a = a % 0.10;

    m5 = (a - a % 0.05)/0.05;   
    a = a % 0.05;

    m6 = (a - a % 0.01)/0.01;

    Console.WriteLine("NOTAS:");
    Console.WriteLine($"{n1} nota(s) de R$ 100.00");
    Console.WriteLine($"{n2} nota(s) de R$ 50.00");
    Console.WriteLine($"{n3} nota(s) de R$ 20.00");
    Console.WriteLine($"{n4} nota(s) de R$ 10.00");
    Console.WriteLine($"{n5} nota(s) de R$ 5.00");
    Console.WriteLine($"{n6} nota(s) de R$ 2.00");
    Console.WriteLine("MOEDAS:");
    Console.WriteLine($"{m1} moeda(s) de R$ 1.00");
    Console.WriteLine($"{m2} moeda(s) de R$ 0.50");
    Console.WriteLine($"{m3} moeda(s) de R$ 0.25");
    Console.WriteLine($"{m4} moeda(s) de R$ 0.10");
    Console.WriteLine($"{m5} moeda(s) de R$ 0.05");
    Console.WriteLine($"{m6} moeda(s) de R$ 0.01");    
  }
}

Answer 1

Let’s assume that the price of a product is R$ 4.99 and you want to know the total value of 17 items of that product.

Below we have the code used to make the calculation using the type float for the product price and of course you will expect the result of R $ 84,83 since 4.99 17 = 84.83. Right?

float preco = 4.99f;

int quantidade = 17;

float total = preco * quantidade;

Console.WriteLine(total);

Console.ReadLine();

You expected 84.83, but the result obtained was 84.82999. To get the right result, you must use the type decimal.

Completion

For any calculation involving money or finance, the type Decimal should always be used. Only this type has the appropriate precision to avoid critical rounding errors.

Source: Using floating point in calculations

Use the suffix M or m for the decimal type.

decimal valor = 0.01m;

Answer 2

Good evening, the syntax with passage of arguments to Console.WriteLine() is Console.WriteLine("{0}{1}{2}", SUA_VAR1, SUA_VAR2, SUA_VAR3) .... because the method contains a parameter that accepts args[] or several variables.

Console.WriteLine($"{m6} moeda(s) de R$ 0.01");

Remove the $, already the {m6} must be your index variable 0 {0}. Put a comma at the end and pass the arguments to function.

When you want to do mathematical operations with two decimal places as for example in coins you should make a arrendomento because the MOD or in the case % using double has very large 64 bit values that we don’t need in the case, use the Math.Round() to round a value to the nearest integer or to the specified number of decimals. There is and you don’t need to calculate the M6 because it is already the rest of the value itself.

Example:

    int n1,n2,n3,n4,n5,n6,m1,m2,m3,m4,m5,m6;
    double a = 576.43f;
    a = Math.Round(a, 2);

    n1 = (int)(a - a % 100)/100;
    a = Math.Round(a % 100, 2);
    n2 = (int)(a - a % 50)/50;
    a = Math.Round(a % 50, 2);
    n3 = (int)(a - a % 20)/20;
    a = Math.Round(a % 20, 2);
    n4 = (int)(a - a % 10)/10;
    a = Math.Round(a % 10, 2);
    n5 = (int)(a - a % 5)/5;
    a = Math.Round(a % 5, 2);
    n6 = (int)(a - a % 2)/2;
    a = Math.Round(a % 2, 2);
    m1 = (int)(a - a % 1)/1;
    a = Math.Round(a % 1, 2);
    m2 = Convert.ToInt32((a - a % 0.50)/0.50);
    a = Math.Round(a % 0.50, 2);
    m3 = Convert.ToInt32((a - a % 0.25)/0.25);
    a = Math.Round(a % 0.25, 2);
    m4 = Convert.ToInt32((a - a % 0.10)/0.10);
    a = Math.Round(a % 0.10, 2);
    m5 = Convert.ToInt32((a - a % 0.05)/0.05);   
    a = Math.Round(a % 0.05, 2);
    m6 = Convert.ToInt32(a/0.01);

    Console.WriteLine("NOTAS:");
    Console.WriteLine("{0} nota(s) de R$ 100.00", n1);
    Console.WriteLine("{0} nota(s) de R$ 50.00", n2);
    Console.WriteLine("{0} nota(s) de R$ 20.00", n3);
    Console.WriteLine("{0} nota(s) de R$ 10.00", n4);
    Console.WriteLine("{0} nota(s) de R$ 5.00", n5);
    Console.WriteLine("{0} nota(s) de R$ 2.00", n6);
    Console.WriteLine("MOEDAS:");
    Console.WriteLine("{0} moeda(s) de R$ 1.00", m1);
    Console.WriteLine("{0} moeda(s) de R$ 0.50", m2);
    Console.WriteLine("{0} moeda(s) de R$ 0.25", m3);
    Console.WriteLine("{0} moeda(s) de R$ 0.10", m4);
    Console.WriteLine("{0} moeda(s) de R$ 0.05", m5);
    Console.WriteLine("{0} moeda(s) de R$ 0.01", m6);