CSE 1321L: Programming and Problem Solving I Lab Lab 9 Multi-Dimensional Arrays

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CSE 1321L: Programming and Problem Solving I Lab Lab 9

Multi-Dimensional Arrays

Lab9A: N by N

Now we have moved from 1-D arrays onto 2-D arrays; please keep in mind that while with 1-D arrays we used one for-loop to traverse the array, with 2-D arrays we need to use a nested for-loop to traverse it.

Ideally, a rule of thumb, is that the outer loop (the “i” loop) would be representative of the row number, and the inner loop (the “j” loop) would be representative of the column number. Together the row number and column number decide what cell is being executed on.

Create a simple program that asks the user for a row and column size for a 2-D integer array, have the program then create such an array. At this point this array’s cells should be filled with zeros since nothing has been done to change the cell values.

Next, have that program dynamically adapt to the sizes of the array (that were provided by the user) and fill the array with numbers ascending from 1 → n (n being the number of the nth cell in that 2-D Array depending on the size). Please then print the array out. Remember, you cannot just print an array out, you have to use loops and print each cell individually.

Please refer to the sample output below for visualization and match its style.

As always:

• Remember, the class name should be Lab9A.

• The user input is indicated in bold.

Sample Output #1:

Please enter the number of rows: 4 Please enter the number of columns: 4

I have 4 rows and 4 columns. I need to fill-up 16 spaces.

The 4x4 array:

1|2|3|4|

5|6|7|8|

9|10|11|12|

13|14|15|16|

Sample Output #2:

The 3x2 array:

1|2|

3|4|

5|6|

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Lab9B: Lab9A, but now with more math

For this exercise you will be writing a program that will be building upon the previous program. So please make a new class file, copy, and rename the code you have already written for Lab9A. Please also remember to rename the file and (and in the case of Java and C# students) class name to Lab9B.

For this exercise, please calculate two values from all of the numbers in the two dimensional array. The first value should be the sum of all numbers in the array. This should be stored in a separate “int” variable that is created outside the nested FOR loops. The second value should be the total average of all numbers in the Array. This should be stored in a separate “float” variable, also outside the nested FOR loop structure.

So, in short:

• Display the sum of the values in the array

• Then display the average of the values in the array

As always:

• Remember, the class name should be Lab9B.

Sample Output #1:

The 3x2 array:

1|2|

3|4|

5|6|

The sum of all the numbers in the 3x2 array: 21 The average of all the numbers in the 3x2 array: 3.5 Sample Output #2:

The 4x4 array:

1|2|3|4|

5|6|7|8|

9|10|11|12|

13|14|15|16|

The sum of all the numbers in the 4x4 array: 136 The average of all the numbers in the 4x4 array: 8.5

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Lab9C: 2D or not 2D

For this exercise you will also be writing a program that will be building upon Lab9A. So please make a new class file, copy, and rename the code you have already written for Lab9A. Please also remember to rename the file and (and in the case of Java and C# students) class name to Lab9C.

For this exercise, please take the array that was filled up with values and flatten it i.e., convert the 2-D array to a 1-D array that contains the same values. Please do not just print the 2-D array to look like a 1-D array

Hint: You will have to take the 2-D array’s total amount of cells and make a 1-D array of the same size.

As always:

• Remember, the class name should be Lab9C.

Sample Output #1:

The 4x4 array:

1|2|3|4|

5|6|7|8|

9|10|11|12|

13|14|15|16|

The 4x4 2-D array flattened into a 16 cell 1-D array:

1|2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|

Sample Output #2:

The 3x2 array:

1|2|

3|4|

5|6|

The 3x2 2-D array flattened into a 6 cell 1-D array:

1|2|3|4|5|6|

Instructions:

• Programs must be working correctly.

• Programs must be saved in files with the correct file name.

• If working in Java or C#, class names must be correct.

• Programs must be working and checked by the end of the designated lab session.

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Appendix – Referencing row or column length C# int[][] grid = new

int[4][5];

To get the row length use arrayname.GetLength(0) E.g.: grid.GetLength(0)

To get the column length use arrayname.GetLength(1) E.g.: grid.GetLength(1)

Java:

int[][] grid = new int[4][5];

To get the row length use arrayname.length E.g.: grid.length

To get the column length use arrayname[0].length E.g.: grid[0].length

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Appendix for C++ Students

One of the most common (and simplest) file formats for storing data is “comma separated values” – or .csv files. You can make these in Microsoft Excel or something even simpler like Notepad or TextEdit. They look like this:

1, 2, 3 4, 5, 6 7, 8, 9

Each data element is separated from the others by comma; note that there’s no comma at the end of the line.

You’ve probably used getline a lot now, but there’s a variation of it that you probably haven’t used. If we pass it three parameters instead of two, the third represents the “delimiter” between the data elements which, in this case, is the comma. However, getline gives us a string, not a number – so we have to convert it to a number using “stoi” (or “string to int”). The code below reads from a file called “matrices.csv” which is located in the “Debug” folder of the project (so it can be found). Note: make this file before coding.

#include <iostream>

#include <fstream>

#include <string>

using namespace std;

void main() {

// Create a filestream object – just like last lab.

fstream fs;

// Open the file for reading using “in”.

fs.open("matrices.csv", fstream::in);

// When we read in from a file, it's a string (s). //

We have to convert that string to a number (i).

string s; int i; int sum = 0;

// While we can read a row/string from the file... continue processing each row while (getline(fs, s, ',')) { // Get the first string, reading up until a comma (1^st)

i = stoi(s); sum += i; // Convert it to an int and add to sum cout << i <<"|"; // Print it out

getline(fs, s, ','); // Get the next value, reading until a comma (2^nd) i = stoi(s); sum += i; // Convert it to an int...

cout << i << "|"; // Print it out

getline(fs, s); // Get the remainder of the string (3^rd) i = stoi(s); sum += i;

cout << i << endl;

}

cout << sum << endl;

// Close the file fs.close(); cin >> s;

// Convert it to an int...

}