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Question about arrays

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Join Date: Oct 2009

Posts: 2

Reputation: zmwg is an unknown quantity at this point

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zmwg

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Newbie Poster

Question about arrays

Oct 18th, 2009

I'm writing a program that takes input for an an array. It then uses a loop to replace the values in another array that has preset values with the values from the array that received input.

When I try to move the values though...well let's say arrayA is the one with the preset values and arrayB is the one that has the inputted values. lw $t3, arrayB($t0) - yields an error, but lw $t3, arrayA($0) works. Is there another command that needs to be used when getting the value from an array that doesn't have preset content?

 Help with Code Tags 
 assembly Syntax (Toggle Plain Text) 
.data
strOutput: .asciiz "Input: "
arrayA: .word 1,2,3,4
arrayB: .space 16
.text		
	.globl main
main:
 
        li	$v0, 4
	la	$a0, strOutput
	syscall		
 
        la 	$t1,arrayB
	li	$v0, 8
	la	$a0, 0($t1)
	syscall
 
	li	$v0, 8
	la	$a0, 4($t1)
	syscall
 
	li	$v0, 8
	la	$a0, 8($t1)
	syscall
 
	li	$v0, 8
	la	$a0, 12($t1)
	syscall
 
        li 	$t0, 0
	lw 	$t3, arrayB($t0)
.data
strOutput: .asciiz "Input: "
arrayA: .word 1,2,3,4
arrayB: .space 16
.text		
	.globl main
main:

        li	$v0, 4
	la	$a0, strOutput
	syscall		

        la 	$t1,arrayB
	li	$v0, 8
	la	$a0, 0($t1)
	syscall

	li	$v0, 8
	la	$a0, 4($t1)
	syscall

	li	$v0, 8
	la	$a0, 8($t1)
	syscall

	li	$v0, 8
	la	$a0, 12($t1)
	syscall

        li 	$t0, 0
	lw 	$t3, arrayB($t0)

I know it's very basic, but I don't know if I'm missing a command or something. Using PCSpim.

And also the number replacement will be done with a loop hence why I'm using arrayB($t0) instead of something else...if that makes any sense at all.

Last edited by zmwg; Oct 18th, 2009 at 9:00 pm.

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Join Date: Jun 2009

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wildgoose

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Practically a Posting Shark

Oct 19th, 2009

I think you misunderstand the syscall function. It doesn't return a four byte integer. It returns a string!
You also aren't setting $a1 to maximum number of characters to read - 1. The function returns the string with a NULL terminaton.

$a0 = buffer
$a1 = sizeof buffer - 1
$v0 = 8 Function read string.

think you meant $v0 = 5 ? Upon return $v0 contains integer read!

Last edited by wildgoose; Oct 19th, 2009 at 12:35 am.

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Join Date: Oct 2009

Posts: 2

Reputation: zmwg is an unknown quantity at this point

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zmwg

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Newbie Poster

Oct 19th, 2009

Ahh...I was copy pasting that part from a previous program. We just started assembly. Staring at the code feels kind of like mind screw compared to other stuff like C++.

I see what you're talking about though, I got it to work now. Thanks.