CS 610: Intermediate Programming: C/C++ Making Programs General An Introduction to Linked Lists

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1 ... 1/17 CS 610: Intermediate Programming: C/C++ Making Programs General An Introduction to Linked Lists Alice E. Fischer Spring 2016

2 ... 2/17 Outline Generic Functions Command Line Arguments Review for Final Exam

3 ... 3/17 Generic Functions I. Generic Functions

4 ... 4/17 Generic Functions C s Generic Functions Work on any Type qsort() and bsearch() Sorting and searching operations are independent of the type of data being processed. You can sort an array of any base type. However, an ordinary program must be edited and recompiled to change the base type of the array. OO languages overcome this limitation by using classes. We can achieve part of this goal by using type void*. These generic functions depend on a specific comparison function to define the meaning of the idea sorted. We can sort in ascending or descending order, and we can sort on a whole data object or one field of a structure.

5 ... 5/17 Generic Functions qsort() and bsearch() These functions are defined in <stdlib.h>. They let you sort or search an array of any base type. qsort() performs a quicksort. bsearch() performs a binary search. The arguments to qsort() are A pointer to the array to sort. Cast the pointer to type void*. The number of items to sort, an int. The size of the base type of the array. A comparison function that defines the sort order. bsearch() has another parameter at the beginning of the list, the key value to search for.

6 ... 6/17 Generic Functions Comparison Functions A qsort comparison function has two const void* parameters. Each one is a pointer to an array element. The two array elements will be compared. The result returned will be 0 if they are equal, negative if the first should sort before the second, and positive if the second should sort before the first. This function is for sorting an array of doubles into ascending order: int ascend ( const void* ap, const void* bp ) { double a = *(double*)ap; double b = *(double*)bp; return a-b; }

7 ... 7/17 Generic Functions Comparing Two Structs If you are sorting an array of structs, the comparison function must select one member of the struct to compare. Here is a function that will compare two CardT values based on the ranks of the two cards. typedef struct {SuitT suit; char rank; int pts;} CardT; int ascend ( const void* ap, const void* bp ) { CardT a = *(CardT*)ap; CardT b = *(CardT*)bp; return a.rank - b.rank; }

8 ... 8/17 Generic Functions Example: Calling qsort() and bsearch() // Sort the array in ascending order. qsort( (void*)data, n, sizeof(double), ascend ); // Search for 12.4 in the sorted array. bsearch(12.4, (void*)data, n, sizeof(double), ascend);

9 ... 9/17 Command Line Arguments II. Command Line Arguments

10 ... 10/17 Command Line Arguments Command Lines A command line is a line of text that you type into a command shell to cause a program to be executed. This method of executing a program is important when you are working through an internet connection to a remote computer. Even on your local machine, sometimes it is just easier to use the command line than to create a project. A command line starts with the name of the program to execute, followed by zero or more arguments. Arguments can include switches, numbers, and file names, in varying combinations. Some arguments are optional. These are normally given before the required arguments. File names are normally last.

11 ... 11/17 Command Line Arguments Command lines in your program: argv and argc When you use the full standard prototype for main: int main ( int argc, char* argv[] ); The operating system will accept information on the command line and deliver it to you through argc and argv. argc tells you how many strings are in the array. argv is an array of whitespace-delimited fields that you typed on your command line, where each field has become a separate null-terminated string. Your job is to analyze these strings and set up your program s internal environment appropriately.

12 ... 12/17 Command Line Arguments Example: argc and argv This is the Unix command that I would use to compile my shuffle program and link it with the tools: gcc -o shuffle -Wall -std=c99 shuffle.c tools.c argc argv 7 gcc -o shuffle -Wall -std=c99 shuffle.c tools.c

13 ... 13/17 Command Line Arguments Example: sorting.c A Command-Line Program to Sort doubles Usage: sorting [-r] maxitems inname outname The arguments to the sorting program are: Optional: -r if you want the numbers in reverse (descending) order An integer, the # of doubles to read from the file and sorted. The name of a file that contains the unsorted data. The name of an output file for sorted data. When a command line is given that does not satisfy the requirements of a program, it is customary to display a usage comment and quit.

14 ... 14/17 Command Line Arguments sorting.c: Interpreting the command line. If the number of arguments is wrong, display a usage comment. Set argp to point at the first argument. If argc is 5, the optional parameter is present. If so, check to be sure it is actually -r. If so, set the boolean variable to indicate we are sorting in reverse (descending) order. Incrememt the argument pointer past the optional argument. Next is the number of doubles to read from the file and sort. Use strtol() to convert this string to an integer. Open the input file (and test). Display an error comment and quit if the output file already exists. Otherwise, open it.

15 ... 15/17 Review for Final Exam V. Review for Final Exam

16 ... 16/17 Review for Final Exam Review for Final Exam 1. Bitwise operators. 2. Two dimensional arrays and subscript functions. 3. Dynamic allocation. (new, delete, and delete[]), (malloc, calloc, realloc, and free). 4. Arrays of pointers to objects. 5. Arrays that can grow by reallocation. (vectors) 6. Using pointers to process arrays. 7. Pointers to functions. Comparison functions, qsort(), and bsearch(). 8. Command-line arguments: concepts, purpose, and code. 9. Recursion on arrays

17 ... 17/17 Review for Final Exam Instructions for Final Exam TBA

Kurt Schmidt. October 30, 2018

Kurt Schmidt. October 30, 2018 to Structs Dept. of Computer Science, Drexel University October 30, 2018 Array Objectives to Structs Intended audience: Student who has working knowledge of Python To gain some experience with a statically-typed