Two-dimensional arrays in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a two-dimensional array in C?

A two-dimensional array in C is like a table with rows and columns. It stores data in a grid format, where each element is accessed by two indexes: one for the row and one for the column.

beginner

How do you declare a two-dimensional array of integers with 3 rows and 4 columns in C?

You declare it like this: int arr[3][4]; This means the array has 3 rows and 4 columns.

beginner

How do you access the element in the 2nd row and 3rd column of a 2D array named arr?

You use arr[1][2]. Remember, counting starts at 0, so the 2nd row is index 1 and the 3rd column is index 2.

intermediate

How can you initialize a 2D array with values at the time of declaration?

You can write: int arr[2][3] = {{1, 2, 3}, {4, 5, 6}}; This sets the first row to 1, 2, 3 and the second row to 4, 5, 6.

intermediate

What happens if you try to access an element outside the declared size of a 2D array?

Accessing outside the declared size causes undefined behavior. This means the program might crash, show wrong data, or behave unpredictably. Always stay within the array bounds.

How do you declare a 2D array with 5 rows and 2 columns in C?

A int arr[5][2];

B int arr[2][5];

C int arr(5,2);

D int arr[5,2];

The correct syntax uses square brackets for each dimension: int arr[5][2];.

What is the index of the first element in a 2D array in C?

A [0][0]

B [1][1]

C [0][1]

D [1][0]

C arrays start at index 0, so the first element is at [0][0].

How do you access the element in the 3rd row and 1st column of arr?

A arr[0][1]

B arr[2][0]

C arr[1][2]

D arr[3][1]

Indexing starts at 0, so 3rd row is index 2 and 1st column is index 0.

Which of these initializes a 2x2 array with all zeros?

A int arr[2][2] = {{0, 0}, {0, 0}};

B int arr[2][2] = {1};

C int arr[2][2] = 0;

D int arr[2][2] = {0};

Using {0} initializes all elements to zero.

What is the risk of accessing arr[4][5] if arr is declared as int arr[3][4]?

A It returns zero

B No risk, it's valid

C Undefined behavior, possible crash

D It automatically resizes the array

Accessing outside the declared size causes undefined behavior and can crash the program.

Explain how to declare, initialize, and access elements in a two-dimensional array in C.

Think of a table with rows and columns.

What are the dangers of accessing elements outside the bounds of a two-dimensional array in C?

Imagine trying to open a door that doesn't exist.