How to apply arraylist with variables in an Object, inside a method using a for loop in c #

Question

A hw was given to us to change a previous hw in C# which used 2d arrays and instead of using 2d arrays we use an Array list with variables declared in an object called Students.

I would like to use a method to calculate a student best mark; however, the method is giving me an error and a warning which are the following:

Error:

CS0161 'Form1.Calc_HighestMarkOutput(int)': not all code paths return a value.

Warning:

CS0162 Unreachable code detected.

Inside the arraylist the user inputed (through use of an overload constructor):

Student Name, Maths Mark, English Mark, Maltese Mark, Email Address.

and since in the method I am returning 3 highest marks in 3 subjects attained by all students, I decided to return an array. which will be accessed by a temporary array inside the main program by selectedindex.

Please help me find the problem.

And thanks in advance.

    public int[] Calc_HighestMarkOutput(int HighestMarkIndex)
    {
        int[] HighestMarkOutput = new int[3];

        int HighestMarkMaths = 0;
        int HighestMarkEnglish = 0;
        int HighestMarkMaltese = 0;
        int TMPHighestMarkMaths = 0;
        int TMPHighestMarkEnglish = 0;
        int TMPHighestMarkMaltese = 0;

        for (int i = 0; i < myStudents.Count; i++) //a loop through an array list.
        {
            if (myStudents[HighestMarkIndex].Maths_Result > HighestMarkMaths)
            {
                TMPHighestMarkMaths = myStudents[HighestMarkIndex].Maths_Result;

                HighestMarkMaths = TMPHighestMarkMaths;
            }
            if (myStudents[HighestMarkIndex].English_Result > HighestMarkEnglish)
            {
                TMPHighestMarkEnglish = myStudents[HighestMarkIndex].English_Result;

                HighestMarkEnglish = TMPHighestMarkEnglish;
            }
            if (myStudents[HighestMarkIndex].Maltese_Result > HighestMarkMaltese)
            {
                TMPHighestMarkMaltese = myStudents[HighestMarkIndex].Maltese_Result;

                HighestMarkMaltese = TMPHighestMarkMaltese;
            }

            HighestMarkOutput[0] = HighestMarkMaths;
            HighestMarkOutput[1] = HighestMarkEnglish;
            HighestMarkOutput[2] = HighestMarkMaltese;

            return HighestMarkOutput;
        }

Unrelated FYI, you seem to be using a generic list, not an ArrayList (which is a good thing because ArrayList is obsolete). — 41686d6564
– 41686d6564, Commented Jul 7, 2019 at 21:10

Olivier Jacot-Descombes · Accepted Answer · 2019-07-08 12:26:41Z

You are getting an error, because the return-statement is inside the loop. If the list is empty, the return statement will never be executed. Also, you know the result only after the loop has finished. So, place the return-statement after the loop.

Since the purpose of this method is to find the highest marks, it makes no sense to pass such an index into the routine as a parameter.

Using foreach is easier than for because you don't have to deal with indexes.

Instead of returning an array, return an unnamed student containing the results. You can drop useless temporary variables.

public Student Calc_HighestMarkOutput()
{
    var result = new Student(); // You also might have to add a default constructor.

    foreach (Student student in myStudents) {
        if (student.Maths_Result > result.Maths_Result) {
            result.Maths_Result = student.Maths_Result;
        }
        if (student.English_Result > result.English_Result) {
            result.English_Result = student.English_Result;
        }
        if (student.Maltese_Result > result.Maltese_Result) {
            result.Maltese_Result = student.Maltese_Result;
        }
    }
    return result;
}

You could also use Math.Max to simplify finding the maximum value

foreach (Student student in myStudents) {
    result.Maths_Result = Math.Max(result.Maths_Result, student.Maths_Result);
    result.English_Result = Math.Max(result.English_Result, student.English_Result);
    result.Maltese_Result = Math.Max(result.Maltese_Result, student.Maltese_Result);
}

With these refactorings, the method shrinks from 22 lines (not counting empty lines and lines containing only a brace) to 7 lines.

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