CODEWITHSUNDEEP
assemblymips
Nick Gilbert
Nick Gilbert

Reputation: 4240

Storing a user's input in MIPS

I'm trying to write a program in MIPS assembly that simply prompts a user for their name and then prints their name back to them. So far my code is

#Program that fulfills the requirements of COS250 lab 1
#Nick Gilbert

.data #Section that declares variables for program
firstPromptString:  .asciiz     "What is your name: "
secondPromptString: .asciiz     "Enter width: "
thirdPromptString:  .asciiz     "Enter length: "

name:           .space      20

firstOutString:     .asciiz     "Hi ______, how are you?"
secondOutString:        .asciiz     "The perimeter is ____"
thirdOutString:     .asciiz     "The area is _____"

.text #Section that declares methods for program
main:
    #Printing string asking for a name
    la $a0, firstPromptString #address of the string to print
    li $v0, 4 #Loads system call code for printing a string into $v0 so syscall can execute it
    syscall #call to print the prompt. register $v0 will have what syscall is, $a0-$a3 contain args for syscall if needed

    #Prompting user for response and storing response
    li $v0, 8 #System call code for reading a string
    syscall
    sw $v0, name


    li $v0, 4 #System call code for printing a string
    la $a0, ($v0) #address of the string to print
    syscall

It prompts the user for their name but as soon as you type one character the code blows up. I'm editing and executing using the MARS IDE for MIPS

Upvotes: 0

Views: 32052

Answers (2)

peaker
peaker

Reputation: 11

our lecturer suggested us to write the code in a high-level language as explicit as possible first, and then convert it to MIPS.

Python example:

prompt = "Enter your name: "
hello_str = "Hello "
name = None

print(prompt)
name = input()
print(hello_str)
print(name)

MIPS assembly code:

.data

prompt: .asciiz "Enter name: (max 60 chars)" 
hello_str: .asciiz "Hello "
name: .space 61 # including '\0'

.text

# Print prompt
la $a0, prompt # address of string to print
li $v0, 4
syscall

# Input name
la $a0, name # address to store string at
li $a1, 61 # maximum number of chars (including '\0')
li $v0, 8
syscall

# Print hello
la $a0, hello_str # address of string to print
li $v0, 4
syscall

# Print name
la $a0, name # address of string to print
li $v0, 4
syscall

# Exit
li $v0, 10
syscall

Hope it helps:)

Upvotes: 0

Jester
Jester

Reputation: 58762

You are not using the read string system call correctly. I suspect you haven't actually looked at the documentation on how to use it. You have to pass two arguments:

$a0 = address of input buffer
$a1 = maximum number of characters to read

So you should do something like:

la $a0, name
li $a1, 20

Nevertheless, this shouldn't cause a crash since $a0 should still hold the address of firstPromptString that you set up for the printing, earlier, and that is valid writable memory.

Upvotes: 2

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