Assembler Program with Character Strings
Write an assembly language homework that prompts the user to enter whatever they want (line/string of characters) followed by ENTER
Call the function to take the string & pass it by where it starts in memory (put in register to set where the string starts). Count how many characters including spaces person entered. The program returns back the number of characters & spaces in the register to return how long the string was via register "You entered: _____ characters". Concert & print out ASCII characters from a number of characters
Solution:
; Registers used:
; R0 = used as argument for traps and functions, as return value and as a temporary register
; R1 = used to point to string and as return value for function div10
; R2 = used to hold ascii value for '0'
; R3 = used to hold the number of total characters in the string
; R4 = used to hold the number of spaces in the string
; R5 = used to hold the negative of ascii space (-32)
; R6 = used to hold temporary result of comparison
; R7 = holds return address in function calls
.ORIG x3000 ; start address of code
; prompt user to enter string
LEA R0, prompt ; load prompt address
TRAP x22 ; print string
LEA R1, prompt ; load string address
; read the string and count total chars and spaces using a loop
AND R3, R3, #0 ; number of characters, start in zero
AND R4, R4, #0 ; number of spaces, start in zero
LD R5, negspc ; load -space to check for spaces
ReadString
TRAP x20 ; read character
TRAP x21 ; echo character
ADD R0, R0, #-10 ; see if character was an enter
BRz readEnd ; if so, end loop
ADD R0, R0, #10 ; restore char
ADD R3, R3, #1 ; else, increment total count
STR R0, R1, #0 ; save character in string
ADD R6, R0, R5 ; see if it was a space
BRnp countNext ; if not a space,count next
ADD R4, R4, #1 ; else, increment space count
countNext
ADD R1, R1, #1 ; advance to next position in string
BR ReadString ; repeat loop
readEnd
STR R0, R1, #0 ; save ending zero in string
; here R3 has the total number of chars read and R4 has the number of spaces
; Print the result:
LEA R0, result1 ; load address of the first result message
TRAP x22 ; print the string
ADD R0, R3, #0 ; copy number of chars
JSR PrintNum ; print number
LEA R0, result2 ; load address of the second result message
TRAP x22 ; print the string
LD R0, newline ; load newline
TRAP x21 ; jump to next line
; Print the space result:
LEA R0, result3 ; load address of the 3rd result message
TRAP x22 ; print the string
; print number of spaces
ADD R0, R4, #0 ; copy number of spaces
JSR PrintNum ; print number
LEA R0, result4 ; load address of the 4th result message
TRAP x22 ; print the string
; print number of non-spaces
ADD R0, R3, #0 ; copy total number of chars
NOT R4, R4 ; take ones complement of number of spaces
ADD R4, R4, #1 ; add 1 to get the negative
ADD R0, R0, R4 ; subtract number of spaces to get the non-spaces
JSR PrintNum ; print number
; Print the last message:
LEA R0, result5 ; load address of the 5rd result message
TRAP x22 ; print the string
LD R0, newline ; load newline
TRAP x21 ; jump to next line
HALT ; terminate the program
; Function to divide number in R0 by 10, returns quotient in R0, remainder in R1
div10
ADD R1, R0, #0 ; copy number to R1
AND R0, R0, #0 ; initialize quotient to zero
divLoop
ADD R1, R1, #-10 ; compare number with 10
BRn endDiv ; if < 10, end division
ADD R0, R0, #1 ; else, increment quotient
BR divLoop ; repeat loop
endDiv
ADD R1, R1, #10 ; restore remainder
RET ; return
; Function to print number in R0, assumes is <100
PrintNum
ST R7, tempR7 ; save return address
JSR div10 ; divide number by 10
LD R2, ascii0 ; load ascii '0'
ADD R0, R0, #0 ; see if the quotient is zero
BRz printLow ; if so, print just low digit
ADD R0, R0, R2 ; convert digit to ascii
TRAP x21 ; print digit
printLow
ADD R0, R1, R2 ; convert low digit to ascii
TRAP x21 ; print digit
LD R7, tempR7 ; restore return address
RET
tempR7 .FILL 0 ; place to save return address
ascii0 .FILL 48
prompt .STRINGZ "Please enter a string: "
result1 .STRINGZ "You entered: "
result2 .STRINGZ " chars"
result3 .STRINGZ "There were "
result4 .STRINGZ " spaces and "
result5 .STRINGZ " non-space characters "
negspc .FILL -32
newline .FILL 10
string .BLKW 100
.END