IS1200 Solution

IS1200/IS1500
Lab2 – C Programming
Introduction
Welcome to the second lab in the course. In this lab, you will learn the basics of the C programming language. More specifically, after finishing this lab, you will be able to
1. construct shorter C programs that includes for-loops, if-statements, arrays, and pointers.
2. analyze C programs and understand how a compiled program is laid out in memory.
Preparations
You must do the lab work in advance, except for a few specific tasks. The teachers will examine your skills and knowledge at the lab session.
Assignments 1 through 5 must be prepared completely before the start of your lab session.
Assignments 6 (the surprise assignment) will be performed during your lab session.
NOTE: In this exercise, you must explicitly declare in the code if you or your lab partner wrote the code. That is, you should explicitly state who actually typed on the computer. It is NOT allowed to copy ANY code from anyone else or from the Internet. Out of the four first assignments, each of you (lab partners) should author two assignments each. This means that it is not allowed that just one of you are sitting and actually typing the code for all assignments. You should still sit together and discuss all the problems and the solutions and the lab partner who is not typing should still be able to analyze the program and explain all the details of the solution. It is also allowed that both of you are creating your own solutions, for all exercises. This is actually the best alternative. It is OK if your solutions are similar, as long as you have written them individually.
Lab Environment
For assignment 5, you will use the MCB32 Tool together with the ChipKit Uno32 board that you received in lab 1.
Reading Guidelines
Review the following course material while you are preparing your solutions.
• Lectures 1 and 4.
• The online C programming tutorial links that are available on the course webpage under “Literature”.
Examination
Examination is grouped into parts. Each part is usually a group of several assignments. Examining one part takes 5–15 minutes. Make sure to call the teacher immediately when you are done with an assignment.
Part 1 – Assignments 1 to 3.
Part 2 – Assignments 4.
Part 3 – Assignment 5 and 6.
The teacher checks that your program behaves correctly, and that your code follows all coding requirements and is easily readable. The teacher will also ask you to compile your program. If there are any errors or warnings, the teacher will ask you to solve these problems before the actual examination can begin.
The teacher will also ask questions, to check that your knowledge of the design and implementation of your program is deep, detailed, and complete. When you write code, make detailed notes on your choices of algorithms, data-structures, and implementation details. With these notes, you can quickly refresh your memory during examination, if some particular detail has slipped your mind.
Assignments
Assignment 1: Basic Control-Flow
The purpose of this assignment is to learn how to write a simple C program that includes basic control structures, including if-statements and for-loops.
Download file prime.c from the course web page. Assuming that you are using gcc as your compiler, compile and run the file as follows.
gcc prime.c -o prime ./prime
The program prints number 0 three times.
Task: Your task is to implement the body of function is_prime(), so that it returns value 1 if parameter n is a prime number, and 0 if it is not. The function must behave correctly for all positive integer numbers. The function should not use any data structures, only simple loops and conditional if-statements.
Assignment 2: Functions and Side Effects
The purpose of this assignment is to learn the concepts of functions, arguments, global variables, and side effects.
Download file print-primes.c from the course web page. Function print_primes includes example code that shows how a list of prime numbers should be printed to the standard output.
Task: You should now do the following:
1. Create a new function called print_number that should have one integer parameter value representing the number that should be printed. If the function is called several times in a row, the output should be printed in several columns, as shown in the example template code. The number of columns is defined by the define COLUMNS. The function should not return any value.
2. Insert function is_prime from the previous exercise. Create a new body for the function print_primes.The function should print all prime numbers from 2 to n by calling functions print_number and is_prime.
If you execute the program as follows:
./print-primes 105
the output should be all prime numbers up to and including 105. That is, the output should be as follows:
2 3 5 7 11 13
17 19 23 29 31 37
41 43 47 53 59 61
67 71 73 79 83 89
97 101 103
Questions for assignment 2
Before the oral exam, you should prepare the answers to the following questions. You will need to be able to answer these questions to pass the assignment.
• What does it mean when a function does not return a value? How do you state that in a program? How can then the function (or more precisely, the procedure) perform anything useful?
• How did you implement the side effect that is needed to make print_number behave correctly?
Assignment 3: Arrays
The purpose of this assignment is to learn how to use arrays in a program.
Task 1: Your task is now to create a new program called sieves.c. This program file should use the main function and the print_number function from the previous exercise. However, instead of using the print_prime function, a new function called print_sieves should be implemented. This function should have one parameter that states the max prime number values. This program should give the same output for a given input as in Assignment 2, but the print_sieves function should implement the algorithm Sieve of Eratosthenes. See the Wikipedia page for an explanation of this old and simple, yet powerful algorithm: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes.
In task 1, you should allocate all data on the stack, using a local array declaration. You must not allocate more memory than necessary. In this case, the memory consumption should not be more than n bytes, where n is the parameter value in function print_sieves.
Task 2: Copy the content of sieves.c to a new file sieves-heap.c. Now, allocate the array data on the heap instead of the stack. Do not forget to release the memory when you do not need to use it anymore.
Questions for assignment 3
Before the oral exam, you should prepare the answers to the following questions. You will need to be able to answer these questions to pass the assignment.
• How did you represent the marking of 'prime' and 'not a prime' in the memory array?
• Which are the main steps in the algorithm? How have you implemented these steps?
• What is the largest prime number that you can print within 2 seconds of computation? What is the largest number you can print within 10 seconds? Is it the same for print_prime.c, sieves.c, and sieves-heap.c? Why or why not?
Assignment 4: Pointers
The purpose of this exercise is to get a detailed understand of pointers and pointer concepts such as dereferencing and pointer arithmetics.
Note: your two C functions (work and copycodes) have to be interchangeable with the assembly language versions. Parameters and results must match, so that the code to call your function is the same as the code to call the corresponding assembly-language function.
If your program is implemented correctly, the following should be printed when executing the program pointers.c:
list1: ASCII codes and corresponding characters.
0x054 'T' 0x068 'h' 0x069 'i' 0x073 's' 0x020 ' ' 0x069 'i' 0x073 's'
0x020 ' ' 0x061 'a' 0x020 ' ' 0x073 's' 0x074 't' 0x072 'r' 0x069 'i'
0x06E 'n' 0x067 'g' 0x02E '.'
list2: ASCII codes and corresponding characters.
0x059 'Y' 0x065 'e' 0x074 't' 0x020 ' ' 0x061 'a' 0x06E 'n' 0x06F 'o'
0x074 't' 0x068 'h' 0x065 'e' 0x072 'r' 0x020 ' ' 0x074 't' 0x068 'h'
0x069 'i' 0x06E 'n' 0x067 'g' 0x02E '.'
Count = 35 Endian experiment: 0x23,0x00,0x00,0x00
Questions for assignment 4
Before the oral exam, you should prepare the answers to the following questions. You will need to be able to answer these questions to pass the assignment.
• Explain how you get the pointer addresses to the two char arrays (text1 and text2) and the counter variable (count) in function work().
• What does it mean to increment a pointer? What is the difference between incrementing the pointer that points to the ASCII text string, and incrementing the pointer that points to the integer array? In what way is the assembler code and the C code different?
• What is the difference between incrementing a pointer and incrementing a variable that a pointer points to? Explain how your code is incrementing the count variable.
• Explain a statement in your code where you are dereferencing a pointer. What does this mean? Explain by comparing with the corresponding assembler code.
• Is your computer using big-endian or little-endian? How did you come to your conclusion?
Is there any benefit of using either of the two alternatives?
Assignment 5: Memory Layout
The purpose of this task is to get a good understanding of how data and code are allocated in the memory. This includes local variables, global variables, pointers, and arrays.
Download and unzip file uno32tests.zip from the course website. This assignment uses the MCB32 tool chain and the ChipKIT board. Please run make and make install to upload the program on the board. As part of the exercise, consider the memory map for PIC32, described in the PIC32 Family Reference Manual, Section 3, page 12: http://ww1.microchip.com/downloads/en/DeviceDoc/60001115H.pdf. The virtual memory map is includes addresses that are visible to the programmer and the processor. In the figure, addresses for different memory sections are given.
Task: Your task is to inspect the file main.c and to browse through the information that is shown on the ChipKIT display. In the main function, a function saveword(string, addr)is called 20 times. This help function saves a string name str and displays this as a separate page on on the ChipKIT display. Together with the text, the address addr (parameter two of saveword) is also displayed, together with the data word (32 bits) that the address addr points to. You can switch pages on the ChipKIT board by clicking the buttons. You should now go through all the 20 different items that are displayed, inspect the code, and be ready to answer the following questions:
Questions for assignment 5
Before the oral exam, you should prepare the answers to the following questions. You will need to be able to answer these questions to pass the assignment.
• Consider AM18, AM19, and AF1. Explain why gv ends up with the incremented value, but m does not.
• Pointer cp is a character pointer that points to a sequence of bytes. What is the size of the cp pointer itself?
• Explain how a C string is laid out in memory. Why does the character string that cp points to have to be 9 bytes?
• Which addresses have fun and main? Which sections are they located in? What kind of memory are they stored in? What is the meaning of the data that these symbols points to?
Before the examination, you should also try to answer the following. When the lab-assistant performs the examination, he/she can also clarify anything that you did not understand with the following questions:
• Which addresses are variables in and gv located at? Which memory sections according to the PIC32 memory map? Why?
• Variables p and m are not global variables. Where are they allocated? Which memory section is used for these variables? Why are the address numbers for p and m much larger than for in and gv?
• At print statement AM5, what is the address of pointer p, what is the value of pointer p, and what value is pointer p pointing to?
• At print statement AM7, what is the address of pointer p, what is the value of pointer p, and what value is pointer p pointing to?
• Consider AM14 to AM17. Is the PIC32 processor using big-endian or little-endian? Why?
Assignment 6: Surprise assignment
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