MIPS Address out of range (MARS)

I'm trying to write a simple code which save string and integer input into an array and then prints them (i will also later add another part which sorts them,but i have to get this to work first).

.data
array: .space 40 #10 elements array
in_name: .asciiz "\nInsert name: "
in_date: .asciiz "\nInsert date (mmdd): "
appt: .asciiz "\nList: "
spaz: .asciiz " "
.text
main: la $s0, array #load array in s0 addi $t0, $zero, 0 #t0=0 counter addi $s1, $zero, 0 #s1=0 array size counter j Input
Input: li $v0, 4 la $a0, in_date syscall #ask date li $v0, 5 syscall #read date add $t1, $zero, $t0 #offset in t1 add $t1, $t1, $t1 #t1*2 add $t1, $t1, $t1 #t1*4 add $s2, $t1, $s0 #array with offset in s2 sw $v0, 0($s2) #save date addi $t0, $t0, 1 #t0++ addi $s1, $s1, 1 #array size counter +1 li $v0, 4 la $a0, in_name syscall #ask name li $v0, 8 syscall #read name add $t1, $zero, $t0 #offset in t1 add $t1, $t1, $t1 #t1*2 add $t1, $t1, $t1 #t1*4 add $s2, $t1, $s0 #array with offset in s2 sw $v0, 0($s2) #save name addi $s1, $s1, 1 #array size counter +1 addi $t0, $t0, 1 #t0++ beq $s1, 10, print #if array size=10 go to print j Input #start over until s1=10 print: la $a0, appt li $v0, 4 syscall #print list addi $t0, $zero, 0 #t0=0 counter
res: add $t1, $zero, $t0 #offset in t1 add $t1, $t1, $t1 #t1*2 add $t1, $t1, $t1 #t1*4 add $s2, $t1, $s0 #array with offset in s2 lw $a0, 0($s2) #load date li $v0, 1 syscall #print data addi $t0, $t0, 1 #t0++ la $a0, spaz #load space li $v0, 4 syscall #print space add $t1, $zero, $t0 #offset in t1 add $t1, $t1, $t1 #t1*2 add $t1, $t1, $t1 #t1*4 add $s2, $t1, $s0 #array with offset in s2 lw $a0, 0($s2) #load name li $v0, 4 syscall #print name addi $t0, $t0, 1 #t0++ la $a0, spaz syscall #print space addi $t0, $t0, 1 #t0++ counter bne $t0, $s1, res #start over until t0=s1 j end end: li $v0, 10 syscall #the end

With MARS i get this: line 75: Runtime exception at 0x004000e4: address out of range 0x00000008. The code seems to read correctly, and it prints the first integer i input, and then i get an error when it tries to print the first string. I'm new to mips so the code is probably really bad, and i have some trouble dealing with arrays. What am i doing wrong?

Edit: Thanks to Michael answer i understood what i was doing wrong, but it looks like i don't understand how to do it correctly. I tried adding this code

 li $a0, 4 li $v0, 9 syscall #space for new word (4bytes) move $a0, $v0 li $a1, 4 li $v0, 8 syscall #read name

before the read_string but i still get the same error. How should i do it?

2 Answers

Syscall 8 (read_string) expects a buffer address in $a0 and a buffer length in $a1. It does not return anything.
So what you're doing here:

li $v0, 8
syscall #read name
...
sw $v0, 0($s2) #save name

is store the syscall number (8) in your array. And later when you try to print the string, there will be an attempt to print whatever is at address 8, which is why you get the address out of range 0x00000008 error.

You need to allocate some memory for each string. Either statically, in the .data or .bss section, or dynamically using the sbrk syscall. Then for each string, pass the pointer to the correspoing buffer and its length to the read_string syscall, and store the pointer in your array.

This is your code:

li $a0, 4
li $v0, 9
syscall #space for new word (4bytes)
move $a0, $v0
li $a1, 4
li $v0, 8
syscall #read name

The solution is to replace the first line with la $a0, 4