# Unit 4C - Code Practice with 2D Arrays

Each coding exercise has its own folder. Open its `.java` file and press **Run** to try it. **Run Tests** checks every graded exercise in this lesson at once.

## Exercise 1

Replace the “ADD CODE HERE” below with the code to declare and create a 3 by 3 two-dimensional int array named `table`. The finished code will print the values 0 to 8.

> Open the `01-arrays2dpractice1` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 2

Replace the “ADD CODE HERE” below with the code to declare and initialize a two-dimensional String array called `students` with the names “Brice, Marvin, Anna” in the first row and “Kamal, Maria, Elissa” in the second. The finished code will print all the names in the array starting with all in the first row followed by all in the second row.

> Open the `02-arrays2dpractice2` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 3

Print the values 47, 51, and 20 by accessing them in the given two-dimensional array.

> Open the `03-arrays2dpractice3` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (3 tests). Its tests check your code, not what it prints: “using arr to access 47”, “using arr to access 51”, “using arr to access 20”.

## Exercise 4

Print the values 8, 3, 87, and 34 by accessing them from the given two-dimensional array.

> Open the `04-arrays2dpractice4` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (5 tests).

## Exercise 5

Print the number of rows in the given two-dimensional array, or the length of the outer array. Then print the number of columns, or the length of each inner array.

> Open the `05-arrays2dpractice5` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (3 tests).

## Exercise 6

Loop through the given two-dimensional array, printing out the values in the first row followed by those in the second row and so on.

> Open the `06-arrays2dpractice6` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 7

Declare and create a two-dimensional array of strings named `colors`. Put the colors (“red”, “yellow”, “blue”) in the first row, and the colors (“orange”, “green”, “purple”) in the second row. Then print every value in the array.

> Open the `07-arrays2dpractice7` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 8

Replace the “ADD CODE HERE” below with the code to count and print the number of 7’s that are in the 2d array. It should print 2.

> Open the `08-arrays2dpractice8` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (3 tests).

## Exercise 9

Replace the “ADD CODE HERE” below with the code to print out the sum of the numbers in the second row of the “table” array. It should print 18.

> Open the `09-arrays2dpractice9` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 10

Replace the “ADD CODE HERE” below with the code to find the sum of the values on the diagonal from [0][0] to [num rows - 1][num rows - 1]. Print the sum. It should print 5.

> Open the `10-arrays2dpractice10` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).

## Exercise 11

Replace the “ADD CODE HERE” below with the code to declare and create a two-dimensional array of integers `numbers` with the numbers (1,2,3) in the first row, and the numbers (4,5,6) in the second row. Then loop through the two-dimensional array, printing out the values in the first row followed by those in the second row.

> Open the `11-arrays2dpractice11` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (3 tests).

## Exercise 12

Replace the “ADD CODE HERE” below with the code to declare and create a two-dimensional array of integers `numbers` with the numbers (1,2,3) in the first row, the numbers (4,5,6) in the second row, and the numbers (7,8,9) in the third row. Then loop through the two-dimensional array, printing out the values in the first row followed by those in the second row and so on.

> Open the `12-arrays2dpractice12` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (3 tests).

## Exercise 13

Given the following array, replace the “ADD CODE HERE” below with 1 line of code to replace the word “purple” with “yellow” using the correct array location.

> Open the `13-arrays2dpractice13` folder and edit `Test1.java`. Press **Run** to try it; **Run Tests** checks it (2 tests).