QtSpim not responding when I load my own file and throws errors when loading other files - mips

Question

I'm trying to load this file but QtSpim stops responding when doing so
# Description : This program reads two user inserted integers and asks the
# user which is their greatest common divisor.
# If the user answers correctly the program congratulates the user, if
# not, the user is asked to try again.
.text
.globl _start
_start:
la $a0, str1 # loads str1 address to $a0
li $v0, 4 # loads $v0 with the contents of $a0 to print it
syscall # prints str1
li $v0, 5 # reads the first user inserted integer from the console and
# stores it to $v0
add $a1, $v0, $zero # stores the first integer from $v0 to $a1
syscall # executes the previous commands
la $a0, str2 # loads str2 address to $a0
li $v1, 4 # loads $v1 with the contents of $a0 to print it
syscall # prints str2
li $v1, 5 # reads the second user inserted integer from the console
# and stores it to $v1
add $a2, $v1, $zero # stores the second integer from $v1 to $a2
syscall # executes the previous commands
la $a0, str3 # loads str3 address to $a0
li $v0, 4 # loads $v0 with the contents of $a0 to print it
syscall # prints str3
jal gcd # calls the method named gcd
syscall
gcd:
# y = a % b;
rem $a3, $a1, $a2 # stores the remainder of the division of the
# first integer with the second to $a3
# while (y != 0) {
# a = b;
# b = y;
# y = a % b;
# }
again:
# y = 0; break;
beq $a3, $zero goto exit # if the contents of $a3 equal zero,
# go to exit
syscall
# a = b;
add $a1, $a2, $zero # stores the contents of the 2nd integer to
# the register of the 1st
syscall
# b = y;
add $a2, $a3, $zero # stores the contentnts of y to the register
# of the 2nd integer
syscall
# y = a % b;
rem $a3, $a1, $a2 # stores the remainder of the division of
# the first integer with the second to $a3
j again # jumps to again to do the next iteration of the
# loop
syscall
exit:
jal printQuestion # calls the method named printQuestion
syscall
printQuestion:
loop:
li $v0, 5 # reads the user's answer from the console and
# stores it to $v0
add $s0, $v0, $zero # stores the user's answer from $v0 to $s0
syscall #executes the previous commands
# s = b;
beq $s0, $a2 goto end # if the contents of $s0 are equal with
# the contents of $a2
la $a0, str5 # loads str5 address to $a0
li $v1, 4 # loads $v1 with the contents of $a0 to print it
syscall # prints str5
la $a0, str6 # loads str6 address to $a0
li $v1, 4 # loads $v1 with the contents of $a0 to print it
syscall # prints str6
j loop # jumps to loop
end:
la $a0, str4 # loads str4 address to $a0
li $v1, 4 # loads $v0 with the contents of $a0 to print it
syscall # prints str4
.data
str1: .asciiz "Please insert the first integer : \n"
str2: .asciiz "Please insert the second integer : \n"
str3: .asciiz "Which is the GCD of the first and second integer? \n"
str4: .asciiz "Congratulations! \n"
str5: .asciiz "Wrong answer. Please try again. \n"
str6: .asciiz "Which is the GCD? \n"
However, when a different file (that I copy pasted to see if it works) does load and I try to run it, I'll get these errors:
Exception occurred at PC=0x00000000
Bad address in text read: 0x00000000
Attempt to execute non-instruction at 0x80000180
Is it my code's fault or is something else wrong?
Edit: I'm using the Simple Machine setting.

Answer 1

Spim expects the user code to start at label main, so without it, it will error when running the code.
So you need to change the _start to main in the label and .global.
The beq $a3, $zero goto exit used in two places in invalid as the beq command expects a comma after the $zeroo, and the label to go to - not 'goto label'
You also have a number of syscall statements, but don't set the values v0 value - you are assuming its still the same, or forgot to do it ? Also in some places it looks like you are seeting v1 when you probally meant to set v0 for the syscall.
For example:
la $a0, str1 # loads str1 address to $a0
li $v0, 4 # loads $v0 with the contents of $a0 to print it
syscall # prints str1
Is setting v0 to 4, getting ready for the print string system, which expects the string it will print in a0 (which you set up)
The next lines:
li $v0, 5 # reads the first user inserted integer from the console and
# stores it to $v0
add $a1, $v0, $zero # stores the first integer from $v0 to $a1
syscall # executes the previous commands
Setting v0 to 5 is getting ready for the reading systecall - not sure what add a1, v0 is supposed to be doing, but after the syscall,, v0 will hold the read value. that now needs be stored somewhere.
Next lines:
la $a0, str2 # loads str2 address to $a0
li $v1, 4 # loads $v1 with the contents of $a0 to print it
syscall # prints str2
You want to print str2 similar to how you printed atr1, so a0 is set to the address str2 (which toy did), v0 needs to be 4 (Not v1)
There are repeated instances of that throught the code, as well as places where you do a syscall without setting v0 at all.