I am starting with assembly language and I want to print a message in the console if the user inputs a negative number.
My code:
.globl main
.data
# program output text constants
prompt:
.asciiz "Please enter a positive integer: "
.text
main:
li $v0, 4 # issue prompt
la $a0, prompt
syscall
li $v0, 5 # get input from the user
syscall
blt $v0, $zero, main # input must be positive
# rest of the code that's executed when the input is positive
From what I know, I can compare between two values and go to a specific target in my code, which in this case, I used blt: "branch less than", which checks if the input by the user $v0 is less than 0 or not, if it is less than 0, the code starts reading from main again.
The output of this code:
Please enter a positive integer: -2
Please enter a positive integer: -3
Please enter a positive integer:
I was able to achieve the looping of the input prompt whenever the user inputs a negative value but I also want to print an error message to the console. How can I do that?
Thanks to Peter's first comment, this does ring a bell. I would like to print the error prompt only when the input is less than zero. The second comment is a bit difficult to understand at my current knowledge of assembly language, but I came up with a solution of using a function for this. Simplifying my question, I want to perform two tasks, first one is printing an error message to the console and the second one is starting the code from main. I put the code to do both of them inside a function
func:
li $v0, 4
la $a0, "Error: Invalid input"
syscall
b main
and call it whenever the user inputs a negative number
main:
li $v0, 4 # issue prompt
la $a0, prompt
syscall
li $v0, 5 # get n from user
syscall
blez $v0, func # n must be positive
Also thanks again for your third comment, I did realize now a mistake I was making, I wasn't checking if the user inputs 0 or not.