C#•8mo ago

Hi I Need Help In Two Dimensional Arrays

How do I check the values below and above the main diagonal in a square array?

78 Replies

Kringe•8mo ago

        int[,] arr =
        {
            { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
            { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 },
            { 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 },
            { 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 }, 
            { 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 }
        };

        Console.WriteLine(arr[0, 4]); //prints out 4
        Console.WriteLine(arr[2, 1]); //prints out 21
        Console.WriteLine(arr[3, 3]); //prints out 33

        int[,] arr =
        {
            { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
            { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 },
            { 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 },
            { 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 }, 
            { 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 }
        };

        Console.WriteLine(arr[0, 4]); //prints out 4
        Console.WriteLine(arr[2, 1]); //prints out 21
        Console.WriteLine(arr[3, 3]); //prints out 33

Does this snippet explain it for you?

AhmadHijaOP•8mo ago

I Didnt Mean It Like That if i want for example to check if all the values below the main diagonal are 0 how im i supposd to do this Can i get some help

SpReeD•8mo ago

Talking about main-diagnal I think you mean a matrix. First off, you need to determine it and next create a method for checking below and above. You need for loops for this; looping through a 2D Array is done by nesting a for loop into another, first loop will iterate through the row and the inner loop through column, like so

int[,] arr =
{
    { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
    { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 },
    { 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 },
    { 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 },
    { 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 }
};

for (int x = 0; x < arr.GetLength(0); x++)
{
    for (int y = 0; y < arr.GetLength(1); y++)
    {
        Debug.Print(arr[x, y].ToString());
    }
}

int[,] arr =
{
    { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
    { 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 },
    { 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 },
    { 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 },
    { 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 }
};

for (int x = 0; x < arr.GetLength(0); x++)
{
    for (int y = 0; y < arr.GetLength(1); y++)
    {
        Debug.Print(arr[x, y].ToString());
    }
}

Kringe•8mo ago

        var size = 10;
        var squareArray = new int[size, size];
        var count = 1;

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                squareArray[i, j] = count;
                count++;
            }
        }

        for (int i = 0; i < size; i++)
        {
            Console.WriteLine($"Diagonal: {squareArray[i, i]}");
            Console.WriteLine($"Above the diagonal: {(i - 1 < 0 ? "out of bounds" : squareArray[i - 1, i])}");
            Console.WriteLine($"Under the diagonal: {(i + 1 >= size ? "out of bounds" : squareArray[i + 1, i])}");
            Console.WriteLine();
        }

        var size = 10;
        var squareArray = new int[size, size];
        var count = 1;

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                squareArray[i, j] = count;
                count++;
            }
        }

        for (int i = 0; i < size; i++)
        {
            Console.WriteLine($"Diagonal: {squareArray[i, i]}");
            Console.WriteLine($"Above the diagonal: {(i - 1 < 0 ? "out of bounds" : squareArray[i - 1, i])}");
            Console.WriteLine($"Under the diagonal: {(i + 1 >= size ? "out of bounds" : squareArray[i + 1, i])}");
            Console.WriteLine();
        }

Is this it?

AhmadHijaOP•8mo ago

bro its like school type of somethhin what is var

Pobiega•8mo ago

Type inference Don't worry about it, tbh

Kringe•8mo ago

mb idk why halve is var and halve is int

AhmadHijaOP•8mo ago

the Question is you need to code a method that returns a true of false if: all the values below the main diagonal are 0 and all the values in the main diagonal and above it need 2 be and number other than 0

SpReeD•8mo ago

Now, that you know how to iterate through a matrix, the rest is up to you, to do the calculations and iterate through the main diagonal. I won't provide you the solution to your homework ¯\_(ツ)_/¯

Kringe•8mo ago

this is what you mean by diagonal right

AhmadHijaOP•8mo ago

bro its like a 30 Q homework i solved everything execpt this thing yea when the row and col are equal

Pobiega•8mo ago

So what exactly are you stuck on? Accessing the array? Figuring out the main diagonal?

AhmadHijaOP•8mo ago

no my problem is how to get the values below and above the main diagonal how the structure of the for is going to be

Pobiega•8mo ago

Well, if the matrix has a cube shape and a side length of... 5 We know the diagonal is 0,0 to 5,5 right?

AhmadHijaOP•8mo ago

yes row = col

Pobiega•8mo ago

If you visualize this array, you quite quickly see a pattern for what is below the diagonal and what is above it

AhmadHijaOP•8mo ago

yea

Kringe•8mo ago

or am I spoiling

Pobiega•8mo ago

A little 🙂

Kringe•8mo ago

he didnt have time to copy 😆

AhmadHijaOP•8mo ago

below the main diagonal the row > col and above the row <col

Pobiega•8mo ago

Okay

AhmadHijaOP•8mo ago

@Kringe

AhmadHijaOP•8mo ago

Kringe•8mo ago

Damn

AhmadHijaOP•8mo ago

i dont want it like that i want to understand bruv

Pobiega•8mo ago

So now you know how to differentiate it What's stopping you from understanding?

Kringe•8mo ago

thats the spirit

AhmadHijaOP•8mo ago

idk what to do tbh

Pobiega•8mo ago

I'm unfortunately on a phone atm, otherwise id write a program that prints the matrix and uses colors to show above/on/below. You know exactly what to do thou

Kringe•8mo ago

Ill do it

AhmadHijaOP•8mo ago

you mean somethin like that

AhmadHijaOP•8mo ago

Pobiega•8mo ago

Sure.

Kringe•8mo ago

do you also have to do something with the second diagonal or only the red one

AhmadHijaOP•8mo ago

i know what i need 2 do but not how to do it only the red one

Pobiega•8mo ago

Combine some loops with an if statement? And then you are more or less done...

AhmadHijaOP•8mo ago

the problem is with the loops

Kringe•8mo ago

Do you know how to use breakpoints?

AhmadHijaOP•8mo ago

like yea but why

Pobiega•8mo ago

Why are the loops a problem? Look at the picture you posted

Kringe•8mo ago

csharp 
        var size = 5;
        var squareArray = new int[size, size];
        var count = 1;

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                squareArray[i, j] = count;
                count++;
            }
        }

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                Console.Write(squareArray[i, j] + "\t");
            }
            Console.WriteLine();
        }

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                if (j > i)
                {
                    Console.WriteLine("Above");
                    Console.WriteLine(squareArray[i, j]);
                }
                else if (j < i)
                {
                    Console.WriteLine("under");
                    Console.WriteLine(squareArray[i, j]);
                }
                else
                {
                    Console.WriteLine("Diagonal");
                    Console.WriteLine(squareArray[i, j]);
                }
            }
        }

csharp 
        var size = 5;
        var squareArray = new int[size, size];
        var count = 1;

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                squareArray[i, j] = count;
                count++;
            }
        }

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                Console.Write(squareArray[i, j] + "\t");
            }
            Console.WriteLine();
        }

        for (int i = 0; i < size; i++)
        {
            for (int j = 0; j < size; j++)
            {
                if (j > i)
                {
                    Console.WriteLine("Above");
                    Console.WriteLine(squareArray[i, j]);
                }
                else if (j < i)
                {
                    Console.WriteLine("under");
                    Console.WriteLine(squareArray[i, j]);
                }
                else
                {
                    Console.WriteLine("Diagonal");
                    Console.WriteLine(squareArray[i, j]);
                }
            }
        }

Set your breakpoint at the inner for loop and just loop through it I think you will understand how it works

AhmadHijaOP•8mo ago

i dont know how to form them

Pobiega•8mo ago

Well you have two options

AhmadHijaOP•8mo ago

im already lost my guy

Pobiega•8mo ago

Either loop through everything and use an if to decide if you want to continue or not Or write your loops cleverly to only target above or below the diagonal The second is better, but might be harder

SpReeD•8mo ago

Try using x and y as variable names, like I did in my example, not i (increment) or j, makes things clearer. Also, if using VS, set a breakpoint with F9, run the code and step through it with F10. Do it, you'll understand that way.

AhmadHijaOP•8mo ago

the second one is the one im supposd to do i will do it just going to eat rn

Kringe•8mo ago

Is that because we talking about squares in this context?

SpReeD•8mo ago

Because we have coordinates in a 2d matrix, like Vector2, representing a single point of data.

Pobiega•8mo ago

X/y are the standard coordinate names

Kringe•8mo ago

y thats what I meant will do thanks

 int size = 5;
 int[,] squareArray = new int[size, size];
 int count = 1;
  
 //populate array
 for (int x = 0; x < size; x++)
 {
     for (int y = 0; y < size; y++)
     {
         squareArray[x, y] = count;
         count++;
     }
 }

 //loop through array 
 for (int y = 0; y < size; y++)
 {
     for (int x = 0; x < size; x++)
     {
         if (x > y)
         {
             Console.WriteLine("Above");
             Console.WriteLine(squareArray[y, x]);
         }
         else if (x < y)
         {
             Console.WriteLine("Under");
             Console.WriteLine(squareArray[y, x]);
         }
         else
         {
             Console.WriteLine("Diagonal");
             Console.WriteLine(squareArray[y, x]);
         }
     }
 }

 int size = 5;
 int[,] squareArray = new int[size, size];
 int count = 1;
  
 //populate array
 for (int x = 0; x < size; x++)
 {
     for (int y = 0; y < size; y++)
     {
         squareArray[x, y] = count;
         count++;
     }
 }

 //loop through array 
 for (int y = 0; y < size; y++)
 {
     for (int x = 0; x < size; x++)
     {
         if (x > y)
         {
             Console.WriteLine("Above");
             Console.WriteLine(squareArray[y, x]);
         }
         else if (x < y)
         {
             Console.WriteLine("Under");
             Console.WriteLine(squareArray[y, x]);
         }
         else
         {
             Console.WriteLine("Diagonal");
             Console.WriteLine(squareArray[y, x]);
         }
     }
 }

changed var to int and added coordinates for clarity

AhmadHijaOP•8mo ago

i will see it when i comeback ty or i will try to solve it when i comeback and if i need it ill look at it i understand it now soo if i want to check if all the values under are 0 i just loop the array and if(row > col) thats it ?

Kringe•8mo ago

Yes nice!

AhmadHijaOP•8mo ago

wait ima show you the solution its wrong bro how am i supposd to do it

Kringe•8mo ago

Could you paste the code

AhmadHijaOP•8mo ago

static bool Q4P141(int[,] mat) { for (int i = 0; i < mat.GetLength(0); i++) for (int j = 0; j < mat.GetLength(1); j++) { if (i > j && mat[i, j] != 0) return false; if (i < j && mat[i, j] == 0) return false; } return true;
} the purpose of the method is to check of all the values below are 0 and above and in the main diagonal are different from 0 aka any other number

Kringe•8mo ago

you are returning after checking the first value

AhmadHijaOP•8mo ago

all the values need to be 0 soo if one value is not 0 you can return false you can say if(i>j) if(ma[i,j]!=0) return false

Kringe•8mo ago

wait that was wrong so to clarify you only are checking the vals under the daigonal right

AhmadHijaOP•8mo ago

under and above

Kringe•8mo ago

and the above condition is

AhmadHijaOP•8mo ago

all the values in the main diagonal and above need to be any number but 0

Kringe•8mo ago

ow mb but i think you turned it around

AhmadHijaOP•8mo ago

can u check it for me

Kringe•8mo ago

okay il make it a bit clearer

            for (int y = 0; y < mat.GetLength(0); y++)
            for (int x = 0; x < mat.GetLength(1); x++)
            {
                Console.WriteLine($"cord {mat[y, x]}");

                if (x > y)
                {
                    Console.WriteLine("Above");
                    if (mat[x, y] == 0)
                        return false;
                }
                else if (x < y)
                {
                    Console.WriteLine("Under");
                    if (mat[x, y] != 0)
                        return false;
                }
            }

            for (int y = 0; y < mat.GetLength(0); y++)
            for (int x = 0; x < mat.GetLength(1); x++)
            {
                Console.WriteLine($"cord {mat[y, x]}");

                if (x > y)
                {
                    Console.WriteLine("Above");
                    if (mat[x, y] == 0)
                        return false;
                }
                else if (x < y)
                {
                    Console.WriteLine("Under");
                    if (mat[x, y] != 0)
                        return false;
                }
            }

I also learned you should x an y for this

AhmadHijaOP•8mo ago

ill try it

Kringe•8mo ago

                if (x >= y)
                {
                    if (x == y)
                        Console.WriteLine("Diagonal");
                    else
                      Console.WriteLine("Above");

                    if (mat[x, y] == 0)
                        return false;
                }

                if (x >= y)
                {
                    if (x == y)
                        Console.WriteLine("Diagonal");
                    else
                      Console.WriteLine("Above");

                    if (mat[x, y] == 0)
                        return false;
                }

if you want to include the diagonal

        static bool Q4P141(int[,] mat)
        {
            for (int y = 0; y < mat.GetLength(0); y++)
            for (int x = 0; x < mat.GetLength(1); x++)
            {
                if (x < y && mat[y, x] != 0)
                    return false;
                if (x >= y && mat[y, x] == 0)
                    return false;
            }

            return true;
        }

        static bool Q4P141(int[,] mat)
        {
            for (int y = 0; y < mat.GetLength(0); y++)
            for (int x = 0; x < mat.GetLength(1); x++)
            {
                if (x < y && mat[y, x] != 0)
                    return false;
                if (x >= y && mat[y, x] == 0)
                    return false;
            }

            return true;
        }

without the comments @ahmadhija🌵 Im gonna go did you figure it out?

AhmadHijaOP•8mo ago

nah its still wrong

Kringe•8mo ago

past the code and the array for me plz

AhmadHijaOP•8mo ago

array code is that

Kringe•8mo ago

it should return true right

        int[,] squareArray = 
        {
            { 1, 1, 1, 1, 1},
            { 0, 1, 1, 1, 1},
            { 0, 0, 1, 1, 1},
            { 0, 0, 0, 1, 1},
            { 0, 0, 0, 0, 1}
        };

        int[,] squareArray2 =
        {
            { 1, 1, 1, 1, 1},
            { 0, 1, 1, 1, 1},
            { 0, 0, 1, 1, 1},
            { 0, 99, 0, 1, 1},
            { 0, 0, 0, 0, 1}
        };

        int[,] squareArray3 =
        {
            { 1, 1, 1, 1, 1},
            { 0, 1, 1, 0, 1},
            { 0, 0, 1, 1, 1},
            { 0, 0, 0, 1, 1},
            { 0, 0, 0, 0, 1}
        };

        Console.WriteLine(Q4P141(squareArray)); //true
        Console.WriteLine(Q4P141(squareArray2)); //false
        Console.WriteLine(Q4P141(squareArray3)); //false

        static bool Q4P141(int[,] mat)
        {
            for (int y = 0; y < mat.GetLength(0); y++)
            for (int x = 0; x < mat.GetLength(1); x++)
            {
                    if (x < y && mat[y, x] != 0)
                        return false;
                    if (x >= y && mat[y, x] == 0)
                        return false;
            }

            return true;
        }

        int[,] squareArray = 
        {
            { 1, 1, 1, 1, 1},
            { 0, 1, 1, 1, 1},
            { 0, 0, 1, 1, 1},
            { 0, 0, 0, 1, 1},
            { 0, 0, 0, 0, 1}
        };

        int[,] squareArray2 =
        {
            { 1, 1, 1, 1, 1},
            { 0, 1, 1, 1, 1},
            { 0, 0, 1, 1, 1},
            { 0, 99, 0, 1, 1},
            { 0, 0, 0, 0, 1}
        };

        int[,] squareArray3 =
        {
            { 1, 1, 1, 1, 1},
            { 0, 1, 1, 0, 1},
            { 0, 0, 1, 1, 1},
            { 0, 0, 0, 1, 1},
            { 0, 0, 0, 0, 1}
        };

        Console.WriteLine(Q4P141(squareArray)); //true
        Console.WriteLine(Q4P141(squareArray2)); //false
        Console.WriteLine(Q4P141(squareArray3)); //false

        static bool Q4P141(int[,] mat)
        {
            for (int y = 0; y < mat.GetLength(0); y++)
            for (int x = 0; x < mat.GetLength(1); x++)
            {
                    if (x < y && mat[y, x] != 0)
                        return false;
                    if (x >= y && mat[y, x] == 0)
                        return false;
            }

            return true;
        }

looks good to me

AhmadHijaOP•8mo ago

let me try it sooo im the one who cant check ty soo if any q i can solve it with this pattern Loop if and then what i want to do

Kringe•8mo ago

depends on the question I guess but everything working now?

AhmadHijaOP•8mo ago

yea

Kringe•8mo ago

nice finally

AhmadHijaOP•8mo ago

luv u man last thing y is row and x is col soo when y>x you are talking below and x is the opposite

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Hi I Need Help In Two Dimensional Arrays