Using the student$\_$inputC.s Download student$\_$inputC.sARM code provided in the Files $-->$ ARM Programs on Canvas and discussed in class expand the code to do all the following:

$1.$ Prompt the user for an input number $($integer$).[$Already in program$]$

$2.$ Print the input number back to the screen. $[$Already in program$]$

$3.$ Prompt the user for an input character. $[$New function$].$ Use $"\%$c$"$ instead of $"\%$d$"$ for the input. This will keep from reading the CR from the previous input.

$4.$ Print the input character back to the screen. $[$New function$].$ Use $"\%$c$"$ for the output.

$5.$ Return control back to the operating system. $[$Already in program$]$

Also modify the code comments to include:

CS$309-01$

Use the Raspberry Pi computer assemble, link and run your program. Once you have it working upload the $.$s as your submission. Name your program yourlastname$2.$s$.$

Here is the code: $($Please add the answer to where it works with this code$)$

@ Filename: student$\_$inputC.s

@ Author: Kevin Preston

@ Purpose: Show CS$309$ and CS$413$ students how to read user inputs from

@ the keyboard. Students are expected to learn ARM assembly in

@ these courses not obscure details about C printf and scanf.

@ In most cases it should be assumed the user provided a valid

@ input.

@

@ History:

@ Date Purpose of change

@ $---------------------$

@ $4-$Jul$-2019$ Changed this code from using the stack pointer to a

@ locally declared variable.

@ $15-$Sep$-2019$ Moved some code around to make it clearer on how to

@ get the input value into a register.

@ $1-$Oct$-2019$ Added code to check for user input errors from the

@ scanf call.

@ $21-$Feb$-2019$ Added comments about $"\%$c$"$ vs $"\%$c$"$ related to scanf.

@

@ Use these commands to assemble, link, run and debug this program:

@ as $-$o student$\_$inputC.o student$\_$inputC.s

@ gcc $-$o student$\_$inputC student$\_$inputC.o

@ $./$student$\_$inputC ;echo $$?$

@ gdb $--$args $./$student$\_$inputC

@ $***********************************************************************$

@ The $=($equal sign$)$ is used in the ARM Assembler to get the address of a

@ label declared in the $.$data section. This takes the place of the ADR

@ instruction used in the textbook.

@ $***********************************************************************$

$.$equ READERROR, $0$ @Used to check for scanf read error.

$.$global main @ Have to use main because of C library uses.

main:

@$*******************$

prompt:

@$*******************$

@ Ask the user to enter a number.

ldr r$0,=$strInputPrompt @ Put the address of my string into the first parameter

bl printf @ Call the C printf to display input prompt.

@$*******************$

get$\_$input:

@$*******************$

@ Set up r$0$ with the address of input pattern.

@ scanf puts the input value at the address stored in r$1.$ We are going

@ to use the address for our declared variable in the data section $-$ intInput.

@ After the call to scanf the input is at the address pointed to by r$1$ which

@ in this case will be intInput.

ldr r$0,=$numInputPattern @ Setup to read in one number.

ldr r$1,=$intInput @ load r$1$ with the address of where the

@ input value will be stored.

bl scanf @ scan the keyboard.

cmp r$0,$ #READERROR @ Check for a read error.

beq readerror @ If there was a read error go handle it$.$

ldr r$1,=$intInput @ Have to reload r$1$ because it gets wiped out.

ldr r$1,[$r$1]$ @ Read the contents of intInput and store in r$1$ so that

@ it can be printed.

@ Print the input out as a number.

@ r$1$ contains the value input to keyboard.

ldr r$0,=$strOutputNum

bl printf

b myexit @ leave the code.

@$***********$

readerror:

@$***********$

@ Got a read error from the scanf routine. Clear out the input buffer then

@ branch back for the user to enter a value.

@ Since an invalid entry was made we now have to clear out the input buffer by

@ reading with this format $\%[^$

$]$ which will read the buffer until the user

@ presses the CR$.$

ldr r$0,=$strInputPattern

ldr r$1,=$strInputError @ Put address into r$1$ for read.

bl scanf @ scan the keyboard.

@ Not going to do anything with the input. This just cleans up the input buffer.

@ The input buffer should now be clear so get another input.

b prompt

@$*******************$

myexit:

@$*******************$

@ End of my code. Force the exit and return control to OS

mov r$7,$ #$0$x$01$ @ SVC call to exit

svc $0$ @ Make the system call.

$.$data

@ Declare the strings and data needed

$.$balign $4$

strInputPrompt: $.$asciz "Input the number:

$"$

$.$balign $4$

strOutputNum: $.$asciz "The number value is: $"\%$d $"$

@ Format pattern for scanf call.

$.$balign $4$

numInputPattern: $.$asciz $"\%$d$"$ @ integer format for read.

$.$balign $4$

strInputPattern: $.$asciz $"\%[^$

$]"$ @ Used to clear the input buffer for invalid

input.

$.$balign $4$

strInputError: $.$skip $100*4$ @ User to clear the input buffer for invalid input.

$.$balign $4$

intInput: $.$word $0$ @ Location used to store the user input.

@ Let the assembler know these are the C library functions.

$.$global printf

$.$global scanf