Error cs1520 class struct or interface method must have a return type

It needs a return type, even if that type is void. This method declares no such type:

public SetGrade(float score)

It does, however, try to return something:

return grade;

That something appears to be a char, so make that the return type:

public char SetGrade(float score)

Though, semantically, it doesn’t seem like this should return anything. The method advertises itself as a setter, and indeed should otherwise be a normal property setter were it not for the fact that it takes a parameter. So just set the value with no return:

public void SetGrade(float score)
{
    if (score>=90.0f)
        grade='A';
    else if (score>=80.0f)
        grade='B';
    else if (score>=70.0f)
        grade='C';
    else if (score>=60.0f)
        grade='D';
    else
        grade='F';
}

(Note also that I replaced your strings like "A" with chars like 'A'. In C# you use single-quotes to make a char literal, which is very different from a string literal.)

Now, there are other issues here as well. I’ve never seen this syntax before:

private int id ();
private string name ();
private char grade ();

If those should just be variables then you don’t want parentheses:

private int id;
private string name;
private char grade;

Also, your constructor isn’t actually doing anything with the values you pass it, it just declares variables within its scope and never sets them:

public Student(int ID, string Name)
{
    int id;
    string name;
}

What you probably wanted to do there was set the class’ private variables:

public Student(int ID, string Name)
{
    id = ID;
    name = Name;
}

Though honestly you could simplify your properties using auto-generated properties. The bulk of the class would then look something like this:

class Student
{
    public int ID { get; private set; }
    public string Name { get; set; }
    public char Grade { get; private set; }

    public Student(int id, string name)
    {
        ID = id;
        Name = name;
    }

    public void SetGrade(float score)
    {
        if (score>=90.0f)
            Grade='A';
        else if (score>=80.0f)
            Grade ='B';
        else if (score>=70.0f)
            Grade ='C';
        else if (score>=60.0f)
            Grade ='D';
        else
            Grade ='F';
    }
}

This is more in keeping with C# naming conventions, reduces a lot of code, and really cleans up the overall look and feel of the class. There’s still more fixes and improvements to be made, both structurally and semantically, but I’ll leave that as an exercise for your study.

Привет, форумчане!
Хотел сделать так что бы окно при запуске появлялось в углу экрана, но столкнулся с ошибкой CS1520 «Метод должен иметь тип возвращаемого значения». Пытался найти решение в интернете, но ничего не нашёл (возможно плохо искал), поэтому хотел спросить у вас. Надеюсь на вашу помощь)
код:

using System;
using System.Drawing;
using System.Windows.Forms;
class MyButtonClass : Form
{

    private TextBox FirstText, SecondText, ThirdText;


    private void InitializeComponent()
    {
        this.SuspendLayout();
        // 
        // MyButtonClass
        // 
        this.ClientSize = new System.Drawing.Size(284, 261);
        this.Name = "MyButtonClass";
        this.StartPosition = System.Windows.Forms.FormStartPosition.Manual;
        this.ResumeLayout(false);

    }

    int n, k, res, v;

    public MyButtonClass()
    {
        v = 0;

        this.Width = 296;
        this.Height = 525;

        FirstText = new TextBox();
        FirstText.Top = 10;
        FirstText.Left = 0;
        FirstText.Height = 50;
        FirstText.Width = 210;
        this.Controls.Add(FirstText);
        //Declare, properties and call a TextBox

        SecondText = new TextBox();
        SecondText.Text = $"";
        SecondText.Top = 50;
        SecondText.Left = 0;
        SecondText.Height = 50;
        SecondText.Width = 210;
        this.Controls.Add(SecondText);
        //Declare, properties and call a TextBox

        ThirdText = new TextBox();
        ThirdText.Text = $"0";
        ThirdText.Top = 100;
        ThirdText.Left = 0;
        ThirdText.Height = 50;
        ThirdText.Width = 210;
        this.Controls.Add(ThirdText);
        //Declare, properties and call a TextBox

    }
    public Form()
    {
        InitializeComponent();
        this.StartPosition = FormStartPosition.Manual;
        this.Location = new Point(0, 0);
    }
    static void Main()
    {
        Application.Run(new MyButtonClass());
        //starting objects of class MyButtonClass
    }
}

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C# error, when trying to execute the code as below

using System;
namespace Examples {
 class Program {
  public static void Main(string[] args) {
   Laptop Lenovo = new Laptop("Lenovo");
   Price("$");
   Processor("i");
   Ram(2);
   HDD(500);
   Laptop Dell = new Laptop("Dell");
   Price("$");
   Processor("i");
   Ram(4);
   HDD(1);
   Laptop Sony = new Laptop("Sony");
   Price("$");
   Processor("i");
   Ram(8);
   HDD(1);
  }
 }
 class Laptop: LaptopBase {
  public LaptopBase(String LaptopName): base(LaptopName) {
   this.LaptopBase = LaptopName;
  }
  class LaptopBase {
   public LaptopBase(String LaptopName) {
    WriteLine(" " + LaptopName);
   }
   public void Price() {
    WriteLine("$" + 1000, "$" + 2000, "$" + 3000);
   }
   public void Processor() {
    WriteLine("i" + 3, "i" + 5, "i" + 7);
   }
   public void Ram() {
    WriteLine(2 + "GB", 4 + "GB", 8 + "GB");
   }
   public void HDD() {
    WriteLine(500 + "GB", 1 + "TB", 1 + "TB");
   }
  }
 }
}

main.cs(31,10): error CS1520: Class, struct, or interface method must have a return type

1 Answers

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        public static void Main(string[] args)
        {
            //Create insatce of Class with Name as "Lenove"
            Laptop Lenovo = new Laptop("Lenovo");
           
            //Using the above instance called the Price Method of Lenovo class, it will print $1000
            Lenovo.Price();
            //Using the above instance called the Price Method of Lenovo class, it will print i3
            Lenovo.Processor();
        


        }
    }
    //Laptop Class inherited from LaptopBase class
    public class Laptop : LaptopBase
    {
        public Laptop(string LaptopName) : base(LaptopName)
        {
            //this is used to set value of constructor
            this.LaptopBase = LaptopName;
        }

        public string LaptopBase { get; }
    }
    //Laptop Base class
    public class LaptopBase
    {
        public LaptopBase(String LaptopName)
        {
            //use Console.WriteLine to print data
            Console.WriteLine(" " + LaptopName);
        }

        public void Price()
        {
            Console.WriteLine("$" + 1000, "$" + 2000, "$" + 3000);
        }
        public void Processor()
        {
            Console.WriteLine("i" + 3, "i" + 5, "i" + 7);
        }
        public void Ram()
        {
            Console.WriteLine(2 + "GB", 4 + "GB", 8 + "GB");
        }
        public void HDD()
        {
            Console.WriteLine(500 + "GB", 1 + "TB", 1 + "TB");
        }
    }
}