CSCI 515 C/C++ Programming Fall 2002

Dr. Creider

CLab 8 Assignment (In lab class)

Calculating two dimension array subscripts using offsets

Write a program to compare the subscripts used to access an element of a dynamically allocated block of memory manipulated as a two dimension array with the actual location represented as an offset. You will not allocate any memory. The virtual array could represent either a compile time array or a dynamically allocated block of memory used as a two dimension array. In main, write code which has a nested loop structure. The outer loop will be used to enter pairs of values which represent row and column dimension sizes. Be sure to tell the user how to stop this loop when he/she is ready to terminate this program. The inter loop will be used to enter pairs of values which represent a row and column subscript. Terminate this loop when the user enters a value of -1 for both the row and column subscript.

Write a function to take the dimension sizes and subscripts values entered by the user and compute the actual subscripts to which the values entered refer and the offset from the starting address of the block of memory.

Examples

Example 1: If you define an array to have 3 rows and 5 columns, and enter the subscripts of -1 for row and 8 for column, the actual location of the element in the array is row 0 and column 3 with an offset of 3.

Example 2: If you define an array to have 5 rows and 2 columns and enter the subscripts of 2 for row and 5 for column, the actual location of the element in the array is row 4 and column 1 with an offset of 9. If you entered the subscripts of 2 for row and 0 for column, the actual location would be row 2 and column 0 with an offset of 4.

Pass to the function the two dimension sizes (number of rows and columns), the row subscript and column subscripts which are the values entered by the user. The function will compute the offset and the actual location (may be the same or different from the values entered by the user) of the element in the array in the form of two subscripts. If the subscript values passed to the function produce an offset which is less than the beginning of the array, assign a value of -1 to the offset. If the subscript values passed to the function produce an offset which is greater than the end of the array, assign a value of -2 to the offset. Use the following formulas to compute the offset and actual subscripts.

offset = row subscript entered * column dimension size + column subscript entered

// if offset is before beginning of array or after end of array do not compute the following

actual row subscript = offset / column dimension size

actual column subscript = offset % column dimension size

Use the parameter passing mode of “pass by reference” to change the value of the last three arguments used in the call to this function. The function will have a total of 7 arguments.

When the program returns to main, test the value of the offset. If the offset is a -1, output a message explaining that the subscripts entered refer to an element before the beginning of the array. If the offset is a -2 output a message that the subscripts refer to an element after the end of the array. If the offset is positive display the dimension sizes of the array, the input subscripts, the actual subscripts and the offset computed by the function. Write the program so that you can test several different dimension sizes with different pairs of row and column subscripts.

Name the file you create, CLAB8. Do Not Use Any Global Variables. Save both the source (cpp file) and object code (exe) on your disk which is turned in at the end of the lab.