COMS Spring Homework 3

Transcription

1 COMS Spring 2011 Homework 3 The main goal of the first homework is to make you familiarize with advanced data types and pointers. There are 6 exercises in this assignment, for a total of 100 points. For each coding Exercise in this assignment you should write a separate file called Exercise_M.c where M stands for the Exercise. For example the file solving Exersise 2 should be named Exercise_2.c. At the top of each file you should put your name and UNI in a comment. Make sure you place comments explaining what your code does. Also, make sure that your code compiles. You will not get any point if your code does not compile. This homework is due on Monday, March 21st at the beginning of class, no exceptions. Put your code (only the source.c files, not the executables) and.txt files in a single folder, name it youruni_hw3 and compress it. For example I would name it mm3233_hw3 because my UNI is mm3233. In order to compress it, go to the directory that contains the youruni_hw2folder and use the following command: tar zcvf youruni_hw3.tar.gz youruni_hw3 Upload the compressed folder to HW3 in CourseWorks. Also, bring a printout of your code and written answers to class. 1. (20 points) Theory questions. Write your answers in a file called youruni_hw3.txt 1.1. Explain all the different usages of the operator * in C Write a program that: Creates four arrays: an array of 10 ints, an array of 10 floats, an array of 10 doubles, and an array of 10 chars Prints the memory addresses of all 10 entries of the array. Use the printf conversion for unsigned integer, "%u" (don t worry about the warnings from gcc) What can you deduce from the numbers printed out about how C stores arrays?

2 1.3. Describe the behavior of the program in Figure 1. What values get printed? Why? 1 #include <stdio.h> 2 3 int main(){ 4 5 int arr[] = { 9, 8, 98, 88, 87, 1, 2, 4, 101, 102, 103, 105 }; 6 int *x = arr+4; 7 int *ptr = &arr[7]; 8 9 arr[*ptr] ++; printf( "First value: %d\n", *ptr ); 12 printf( "Second value: %d\n", *x ); 13 *x = 7; 14 printf( "Third value: %d\n", arr[4] + *ptr); return(0); } Figure 1 2. (20 points) Structs 2.1. Generate a list of cars for an automobile vendor with the entries of Figure 2. Each car entry has a year, make, model, price, and a list of people interested in buying it Each car entry must be represented with a struct 2.3. Each person interested in buying cars must be represented with a struct with two fields: name and amount of money willing to pay to buy a car 2.4. Write a program to determine and print to screen all the information about the cars that can be sold (that is, for which a person is offering to pay at least the price of the car)

3 Figure 2

4 3. (20 points) Booleans. Write code to define Booleans in C You have to create a new type, named bool, that can have only two values, true or false. (this part must be done in one line!) 3.2. Create a function called XNOR that takes two Booleans x and y as input and returns the Boolean result according to Table Write a small main function showing that your function XNOR() works correctly for all the input cases presented in Table1. x y result false false true false true false true false false true tue true Table 1 4. (10 points) Pointers. Write a function named removecharacter() that 4.1. Takes 4 inputs: an integer num, a string tr, a string s and a character c, but does not return anything Finds the number of all the occurrences of c in s (both capital and lower case) and saves it in num 4.3. Copies the trimmed string in tr 4.4. Write in the same file a main() function containing a series of tests to showcase the correct behavior of removecharacter(). Note: you can print only from the main function

5 5. (20 points) Arrays of Pointers. Write the function first_last(), defined as follows, that: void first_last( char *s[], int n, char **first, char **last ) 5.1. given an array s of n strings, finds the first and last string in the array according to alphabetical order the function should work with the main() function (which you also have to complete) in Figure 3. int main ( ) { char *array [ ] = { "hello", "world ", "today", "is", " a ", "very", "nice", "day" } ; int size = 8 ;... mins ;... maxs; first_last( array, size, &min, &maxs ) ; printf ( "The first word is %s and the last is %s \ n ", mins, maxs ) ; } return(0); Figure 3 Figure 3 6. (10 Points) Macros. Implement each of the following functions using macros. Implement them all in the same program. Each macro should be named FUNCNAME_HW4 (for example, your implementation of isalpha() should be called ISALPHA_HW4 ). Showcase their use by invoking them in the main function of your program. You may assume that the input c is a char. isalpha(c) : returns 1 if c is an alphabet character a - z, A - Z, otherwise returns 0 isdigit(c) : returns 1 if c is a digit 0-9,, otherwise returns 0 isalnum(c) : returns isalpha(c) or isdigit(c) iscntrl(c) : returns 1 if c is a control char (i.e. \n, \t, \b), otherwise returns 0 islower(c), isupper(c) : returns 1 if c is lowercase/uppercase, otherwise returns 0