Two-Dimensional Data Class of 5 students Each student has 3 test scores Store this information in a two- dimensional array First dimension: which student 0, 1, 2, 3 or 4 Second dimension: which test score 0, 1, or 2

Declaring a 2D Array Give a second pair of square brackets to tell C++ you want a 2D array Example: int grades[5][3];

Creating a 2D Array Create array elements by telling how many ROWS and COLUMNS Example: int grades[5][3]; grades is a two-dimensional array, with 5 rows and 3 columns. One row for each student. One column for each test. C++ arrays are row major, which means that we always refer to the row first.

Initializing Elements // First student scores grades[0][0] = 78; grades[0][1] = 83; grades[0][2] = 82; Write assignment statements to fill-in the rest of the array.

Declare & Create & Initialize Short Cut Example: int grades[5][3] = { { 78, 83, 82 }, { 90, 88, 94 }, { 71, 73, 78 }, { 97, 96, 95 }, { 89, 93, 90 } }; A Two-D Array is an array of arrays. Each row is itself a One-D array.

Row, Column Indices Give both the ROW and COLUMN indices to pick out an individual element. The fourth student’s third test score is at ROW 3, COLUMN

What are the elements of the array table ? int table[3][4]; x = 1; for (row = 0; row < 3; row++) for (col = 0; col < 4; col++) { table[row][col] = x; x++; } //for col column row

Exercise: Average Overall Find the average test score of all students’ test scores. Use rows to tell you how many rows in the 2D array. Use cols to tell you how many columns in the 2D array.

Exercise: Average Overall int sum = 0; for(int r = 0; r < rows; r++) for(int c = 0; c < cols; c++) sum = sum + grades[r][c]; int avg = sum / (rows*cols);

Write a function that prints out the elements in a 2-D array (as they appear in the matrix)

Exercise: print 2-D array void printArray(int matrix[][]) { for(int i = 0; i < matrix.length; i++) { for(int j = 0; j < matrix[0].length; j++) cout << (matrix[i][j] << ” “); cout << endl; }

Write a function that returns the maximum element in a 2-D array. Things work pretty much the same way with 3-D arrays (and 4-D and …)

Exercise: find maximum in a 2D array int findMax(int matrix[][COLS], int r, int c) { int max = matrix[0][0]; for(int i = 0; i < r; i++) for(int j = 0; j < c; j++) if ( matrix[i][j] > max) max = matrix[i][j]; return max; }