CS61C Spring 2012 HW2

Goals

This assignment is designed to give you some practice with C and a bit of review on binary and hexadecimal from section.

Submission

Copy the contents of ~cs61c/hw/sp12/hw2 to a suitable location in your home directory to obtain files you will want for this homework.

	mkdir ~/hw2
	cp -r ~cs61c/hw/sp12/hw2/ ~/hw2	
	

In this directory, there should be files named hw2.txt and bitcount.c. Put your solutions to problems 1 and 2 in hw2.txt, and problem 3 in bitcount.c.
Then run submit hw2. Make sure both files are submitted.

Problem 1

a) Convert 10001001 in binary to decimal (under the unsigned number representation) and hexadecimal.

b) Convert 35 in decimal to binary and hexadecimal.

c) P&H (Revised 4th) exercise 2.33.2 for option b:
Convert this function into pointer-based code.

	  void shift(int a[], int n) {
	     int i;
	     for(i = 0; i != n-1; i++)
	        a[i] = a[i+1];
	  }
	

Problem 2

a) Complete the following setName, getStudentID, and setStudentID functions. You may assume the pointers given are valid and not null.

	#define MAX_NAME_LEN 127
	
	typedef struct {
		char name[MAX_NAME_LEN + 1];
		unsigned long sid;
	} Student;
	
	/* return the name of student s */
	const char* getName (const Student* s) {
		return s->name;
	}
	
	/* set the name of student s
	If name is too long, cut off characters after the maximum number of characters allowed.
	*/
	void setName(Student* s, const char* name) {
		/* fill me in */
	}
	
	/* return the SID of student s */
	unsigned long getStudentID(const Student* s) {
		/* fill me in */
	}
	
	/* set the SID of student s */
	void setStudentID(Student* s, unsigned long sid) {
		/* fill me in */
	}
	

b) What is the logical error in the following function?

	Student* makeAndrew(void) {
		Student s;
		setName(&s, "Andrew");
		setStudentID(&s, 12345678);
		return &s;
	}
	

Problem 3

a) Write a function bitCount() in bitcount.c that returns the number of 1-bits in the binary representation of its unsigned integer argument.
To compile bitcount.c and create an executable named bitcount:

	gcc -std=c99 -o bitcount bitcount.c
	

Remember to fill in the identification information and run the completed program to verify correctness.

	/*
	Name:
	Lab section time:
	*/
	
	#include <stdio.h>
	int bitCount(unsigned int n);
	
	int main(void) {
		printf ("# 1-bits in base 2 representation of %u = %d, should be 0\n", 0, bitCount (0));
		printf ("# 1-bits in base 2 representation of %u = %d, should be 1\n", 1, bitCount (1));
		printf ("# 1-bits in base 2 representation of %u = %d, should be 17\n", 2863377066u, bitCount(2863377066u));
		printf ("# 1-bits in base 2 representation of %u = %d, should be 1\n", 268435456, bitCount(268435456));
		printf ("# 1-bits in base 2 representation of %u = %d, should be 31\n", 4294705151u, bitCount(4294705151u));
		return 0;
	}
	
	int bitCount(unsigned int n) {
		/* your code here */
	}
	

b) You have decided that you want your bitcount program above to work from the command-line (see K&R Section 5.10), as follows:

	# ./bitcount 17
	2
	# ./bitcount 255
	8
	# ./bitcount 10 20
	too many arguments!
	# ./bitcount
	[the same result as from part a]
	

Edit your bitcount.c to include this functionality. You may assume that the single argument will always be an integer in the range from 0 to 2³¹-1. You will find the function atoi helpful.

Extra for experts: Implement this exercise without using the library function atoi (or something comparable). (You don't actually get extra points for this).