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I am learning MIPS as a part of my Computer Organization class at school and I am writing a simple program that reads in a positive integer from the user and tells the user whether the number is even or odd. The program works, but the way I had to split the loop and conditionals into different labels concerns me a little bit.

I could not figure out another way to do it, but as loops and conditionals are very common in code, I want to see if there is a way to do it without creating so many labels. If and when I tackle a bigger project in MIPS, I do not want to have to have 10 different loop labels if there is a better way to do it.

.data
        prompt: .asciiz "\nEnter a integer: "
        even_msg: .asciiz "\nThe number is even.\n"
        odd_msg: .asciiz "\nThe number is odd.\n"
        goodbye: .asciiz "\nGoodbye!\n"
.text

main:
        j loop

loop:
        la $a0, prompt
        li $v0, 4
        syscall

        # Read in value
        li $v0, 5
        syscall

        # If number is negative, exit program.
        slt $t0, $v0, $zero
        bne $t0, $zero, exit

        # Call even_or_odd on value
        add $a0, $v0, $zero
        jal even_or_odd
        j loop

even_or_odd:
        addi $t0, $zero, 2 # Set divisor to 2
        div $a0, $t0
        mfhi $t0           # Save remainder
        beq $t0, $zero, even
        j odd

even:
        la $a0, even_msg        
        li $v0, 4
        syscall
        j return
odd:
        la $a0, odd_msg
        li $v0, 4
        syscall
        j return

return:
        lw $t0, 0($sp)  
        addi $sp, $sp, 4
        jr $ra

exit:
        la $a0, goodbye 
        li $v0, 4
        syscall

        li $v0, 10
        syscall
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  • \$\begingroup\$ If you look at the binary representations of the numbers, you'll notice a pattern that holds for all even and odd numbers that makes parity checking very simple. \$\endgroup\$ – kamoroso94 Feb 4 '18 at 21:01

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