Is there any way to decrease the amount of Else and if?

Question

I should create the conditions for enrolling students based on their age, I was wondering if there is any way to decrease the amount of if in that part of the code:

int idade = Convert.ToInt32(txtAnoUltimoAniversario.Text) - Convert.ToInt32(txtAnoNascimento.Text);
            if (idade > 17)
            {
                lblCategoria.Text = "Adulto";
            }
            else if (idade < 13)
            {
                lblCategoria.Text = "Juvenil B";
            }
            else if (idade < 10)
            {
                lblCategoria.Text = "Juvenil A";
            }
            else if (idade < 7)
            {
                lblCategoria.Text = "Infantil B";
            }
            else if (idade <= 5)
            {
                lblCategoria.Text = "Infatil A";
            }
            else
            {
                lblCategoria.Text = "Não existe categoria";
            }



        }

Answer 1

Even before version 8 in essence it does not (see below it looks much better in newer versions), at least not in a worthwhile way. It is possible to shorten the code and it is possible to fix a problem when the data is typed wrong that is not contemplated there. I also think there’s a logic problem in this whole comparison, but you can’t say.

if (!int.TryParse(txtAnoUltimoAniversario.Text, out var aniversario) || !int.TryParse(txtAnoNascimento.Text, out var ano) {
    //faz alguma coisa aqui para indicar que os dados foram digitados errados
    //Pode ser que seja dizer que não tem categoria, precisa pensar na UX
}
var idade = aniversario - ano;
if (idade < 6) lblCategoria.Text = "Infatil A";
else if (idade < 7) lblCategoria.Text = "Infantil B";
else if (idade < 10) lblCategoria.Text = "Juvenil A";
else if (idade < 13) lblCategoria.Text = "Juvenil B";
else if (idade > 17) lblCategoria.Text = "Adulto"; //e os que estão entre 13 e 17 não existem?
else lblCategoria.Text = "Não existe categoria";

I thought about using a dictionary, but I wouldn’t hurt the performance to do something that would have a larger number of lines than the direct solution. If it had greatly reduced the number of lines maybe I would, but not in this case, including because there may be exceptions in the future that the dictionary does not even work.

What you can do is shorten the code a little more by putting a short name variable with the strings and then attribute it to label.

I made a slightly different code to test:

using static System.Console;

public class Program {
    public static void Main() {
        Compara(20, 15);
        Compara(20, 14);
        Compara(20, 11);
        Compara(20, 8);
        Compara(20, 2);
    }
    private static void Compara(int aniversario, int ano) {
        var idade = aniversario - ano;
        string texto;
        if (idade < 6) texto = "Infatil A";
        else if (idade < 7) texto = "Infantil B";
        else if (idade < 10) texto = "Juvenil A";
        else if (idade < 13) texto = "Juvenil B";
        else if (idade > 17) texto = "Adulto"; //e os que estão entre 13 e 17 não existem?
        else texto = "Não existe categoria";
        WriteLine(texto);
    }
}

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.

A switch would leave even bigger, but in C# 8 has a syntax that can be useful to use the switch, with 9 even better:

using static System.Console;

public class Program {
    public static void Main() {
        Compara(20, 15);
        Compara(20, 14);
        Compara(20, 11);
        Compara(20, 8);
        Compara(20, 2);
    }
    private static void Compara(int aniversario, int ano) => WriteLine((aniversario - ano) switch {
            < 6 => "Infatil A",
            < 7 => "Infantil B",
            < 10 => "Juvenil A",
            < 13 => "Juvenil B",
            > 17 => "Adulto",
            _ =>  "Não existe categoria",
        });
}

Behold working in the .NET Fiddle. Also put on the Github for future reference.

Shorter and more efficient than dictionary option.

Answer 2

Can use a dictionary alternatively:

var idade = 12;

var dic = new Dictionary<int, string>
{
    { 6, "Infatil A" },
    { 7, "Infatil B" },
    { 10, "Juvenil A" },
    { 13, "Juvenil B" },
    { 18, "Não existe categoria" },
    { int.MaxValue, "Adulto" },
};

var result = dic.OrderBy(k => k.Key).FirstOrDefault(e => idade < e.Key).Value;