Difference between revisions of "CSC231 Homework 5 Fall 2017"
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* Submit your program in the '''Homework 5, Problem 2''' section on Moodle. | * Submit your program in the '''Homework 5, Problem 2''' section on Moodle. | ||
+ | <br /> | ||
+ | =Problem 3= | ||
+ | <br /> | ||
+ | Same as with Problem 2, but this time the triangle is reversed: | ||
+ | <br /> | ||
+ | ;Example | ||
+ | |||
+ | cs231a@aurora $ ./hw5c | ||
+ | > Hal-lo-we-en | ||
+ | H | ||
+ | Ha | ||
+ | Hal | ||
+ | Hal- | ||
+ | Hal-l | ||
+ | Hal-lo | ||
+ | Hal-lo- | ||
+ | Hal-lo-w | ||
+ | Hal-lo-we | ||
+ | Hal-lo-we- | ||
+ | Hal-lo-we-e | ||
+ | Hal-lo-we-en | ||
+ | |||
+ | <br /> | ||
+ | * Submit your program to the '''Homework 5, Problem 3''' section on Moodle. | ||
+ | <br /> | ||
+ | =Problem 4= | ||
<br /> | <br /> |
Revision as of 08:49, 30 October 2017
--D. Thiebaut (talk) 09:27, 30 October 2017 (EDT)
Preparation
For this assignment you will need to downloaded an updated version of 231Lib.asm, which has been augmented with a new function for reading strings.
getcopy 231Lib.asm
An example program using the new function, _getString(), is shown below:
;;; ; hw5Prep.asm ;;; ; D. Thiebaut ;;; ; ;;; ; Gets a string from the user and prints it back ;;; ; ;;; ; to assemble and run: ;;; ; ;;; ; nasm -f elf hw5Prep.asm ;;; ; nasm -f elf 231Lib.asm ;;; ; ld -melf_i386 -o hw5Prep hw5Prep.o 231Lib.o ;;; ; ./hw5Prep ;;; ; ------------------------------------------------------------------- ;;; ------------------------------------------------------------ ;;; data areas ;;; ------------------------------------------------------------ section .data prompt db "> " ;;; ------------------------------------------------------------ ;;; code area ;;; ------------------------------------------------------------ section .text global _start extern _getString extern _printString extern _println _start: ;; prompt the user mov ecx, prompt mov edx, 2 call _printString ;; get a string from the user ;; _getString returns the address of the string read in ecx, ;; and the number of chars read in edx call _getString ;; since ecx and edx already contain the address and number ;; of chars, we can directly call _printString, which needs ;; the string and number of chars in the same registers call _printString ;; print a line-feed char. call _println ;;; exit() mov eax,1 mov ebx,0 int 0x80 ; final system call
Create a version of this program in your account, and play with it. Verify that it gets a string from you and prints it back.
Notes
- _getString saves the string in an array declared inside 231Lib.asm. This array contains at most 1000 bytes.
- when _getString returns to your main program, it will set ecx to the address of the array containing the string, and it will set edx to contain the number of characters the user typed at the keyboard.
- the user indicates the end of the string by pressing the ENTER key. The string does not contain the ENTER character (line-feed).
- although I didn't do that here because the program is so simple and short, it is a good idea, just after returning from a call to _getString, to save ecx and edx into two different variables in memory that will hold the address of the string and the number of chars entered at the keyboard.
Problem 1
Write a program called hw5a.asm that prompts the user for a string, and prints it back several times. The number of times the string is printed is the same as the number of characters in the string.
- Examples
cs231a@aurora ~ $ ./hw5a > B B
cs231a@aurora ~ $ ./hw5a > a a
cs231a@aurora ~ $ ./hw5a > hello hello hello hello hello hello
cs231a@aurora $ ./hw5a > chocolate chocolate chocolate chocolate chocolate chocolate chocolate chocolate chocolate chocolate
cs231a@aurora $ ./hw5a > Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween Hall o ween
- Submit your program in the Homework 5, Problem 1 section on Moodle.
Problem 2
Modify your solution program for Problem 1 so that it removes the last character of the previous printed string as it goes through the loop:
- Examples
cs231a@aurora $ ./hw5b > Hall-o-ween Hall-o-ween Hall-o-wee Hall-o-we Hall-o-w Hall-o- Hall-o Hall- Hall Hal Ha H
cs231a@aurora $ ./hw5b > a a
cs231a@aurora ~/HWs/HW5/PB2 $ ./hw5b > 123456789 123456789 12345678 1234567 123456 12345 1234 123 12 1
- Submit your program in the Homework 5, Problem 2 section on Moodle.
Problem 3
Same as with Problem 2, but this time the triangle is reversed:
- Example
cs231a@aurora $ ./hw5c > Hal-lo-we-en H Ha Hal Hal- Hal-l Hal-lo Hal-lo- Hal-lo-w Hal-lo-we Hal-lo-we- Hal-lo-we-e Hal-lo-we-en
- Submit your program to the Homework 5, Problem 3 section on Moodle.
Problem 4