Engineering Problem Solving with C++, Etter/Ingber Chapter 7 Two-Dimensional Arrays and Matrices Engineering Problem Solving with C++, second edition, J. Ingber

Two Dimensional Arrays Declaration and Initialization Computation and Output Function Arguments Engineering Problem Solving with C++, second edition, J. Ingber

Declaration and initialization Engineering Problem Solving with C++, second edition, J. Ingber

Declaration and Initialization The declaration of a two-dimensional array requires a row size and a column size. A consecutive block of (row size)(*column size) memory locations are allocated. The name of the array holds the address of the first byte of memory. Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Example: //Declaration int data[2][3]; Memory Snapshot data ? ? ? ? ? ? Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Example: //Declaration int data[2][3]; row/column form: col 0 col 1 col 2 ? row 0 row 1 Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Example: //Declaration and Initialization double t[2][2] = { {0.1,0.2}{1.1, 1.2} }; Memory Snapshot t 0.1 0.2 1.1 1.2 row 0 0.1 0.2 1.1 1.2 row 1 col 0 col 1 Engineering Problem Solving with C++, second edition, J. Ingber

Two-Dimensional Arrays A two dimensional array stores data as a collection of rows and columns. Each element of a two-dimensional array has a row position and a column position. To access an element in a two-dimensional array, you must specify the name of the array followed by: a row offset a column offset Engineering Problem Solving with C++, second edition, J. Ingber

Example: Input Using cin Nested for loops are often used when inputting and assigning values to a two-dimensional array. Example: double table[RSIZE][CSIZE]; for (int i=0; i<RSIZE; ++i) //every row for (int j=0; j<CSIZE; ++j )//every col cin >> table[i][j]; Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Example: Assignment Example: int v[RSIZE][CSIZE]; for (int i=0; i<RSIZE; ++i) //every row for (int j=0; j<CSIZE; ++j )//every col v[i][j] = i+j; V 1 2 3 Engineering Problem Solving with C++, second edition, J. Ingber

Computation and output computing an average formatted output function arguments Computation and output Engineering Problem Solving with C++, second edition, J. Ingber

Computation and Output The for statement is useful when performing computations on arrays. The index variable of the for statement can be used as an array offset. Computations can be easily performed on an entire two-dimensional array, or on a sub set of the array. Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Computations Compute the average of an array with n rows and m columns. for(int i=0; i<n; ++i) { for(int j=0; j<m; ++j) sum+=array[i][j]; } average = sum/(n*m); Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Computations Compute the average of the nth row of a two-dimensional array with r rows and c columns. for(int col=0; col < c; ++col) { sum += array[n][col]; } rowAverage = sum/c; Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Modify! Modify the C++ statements on the previous slide to compute the average of the nth column. Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Output Two dimensional arrays are often printed in a row by row format, using nested for statements. When printing the row values of an array, be sure to print: whitespace between the values in a row. a newline character at the end of each row. Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Printing 2-D Array for(int r=0; r<NROWS; ++r) { for(int c=0; c<NCOLS; ++c) cout << twoDArr[r][c] << " "; } cout << endl; Engineering Problem Solving with C++, second edition, J. Ingber

Engineering Problem Solving with C++, second edition, J. Ingber Functions Arguments 2-D arrays are always passed by reference. All dimensions of the array, except the leftmost one (row), must be specified. The leftmost one may be empty [] Function prototype example: int rowAverage(int Arr[][COLSIZE], int whichRow); Array declaration in main: int table [ROWSIZE][COLSIZE]; Function invocation example: avg = rowAverage(table, 3); Engineering Problem Solving with C++, second edition, J. Ingber