Detect Add overflow - overflow

Question

What would be a good loop to check when overflow occurs in the mips code I have bellow? It is a program i've came up with to balance a checkbook by basically adding deposits to the account. I just keep getting incorrect values when overflow occurs. I need a loop that detects that overflow would occur if the value is accepted and then asks for another value without accepting the bad value.
# Functional Description:
# This program can be used to balance your check book.
# <DESCRIBE OVERFLOW FEATURE HERE>
#####################################################################
# Pseudocode:
# Print Header;
# s0 = 0;
# loop: Prompt user for transaction;
# v0 << transaction amount;
# if (v0 = 0) done;
# s0 = s0 + v0;
# PSEUDOCODE FOR OVERFLOW DETECTION ALGORITHM HERE>
# cout << s0
# go to loop
# done:
# cout << "Adios Amigo"
#
######################################################################
# Register Usage:
# $v0: Transaction Amount
# $s0: Current Bank Balance
# <HERE YOU DECLARE ANY ADDITIONAL REGISTERS USED>
######################################################################
.data # Data declaration section
Head: .ascii "\n\tThis program, written by <YOUR NAME>,"
.ascii " can be used to balance your check book."
.asciiz "\n\n\t\t\t\t\t\t\t\t\t Balance"
tabs: .asciiz "\t\t\t\t\t\t\t\t\t"
tran: .asciiz "\nTransaction:"
bye: .asciiz "\n **** Adios Amigo **** "
.text # Executable code follows
main:
li $v0, 4 # system call code for print_string
la $a0, Head # load address of Header message into $a0
syscall # print the Header
move $s0, $zero # Set Bank Balance to zero
loop:
li $v0, 4 # system call code for print_string
la $a0, tran # load address of prompt into $a0
syscall # print the prompt message
li $v0, 5 # system call code for read_integer
syscall # reads the amount of Transaction into $v0
beqz $v0, done # If $v0 equals zero, branch to done
addu $s0, $s0, $v0 # add transaction amount to the Balance
li $v0, 4 # system call code for print_string
la $a0, tabs # load address of tabs into $a0
syscall # used to space over to the Balance column
li $v0, 1 # system call code for print_integer
move $a0, $s0 # move Bank Balance value to $a0
syscall # print Bank Balance
b loop # branch to loop
done: li $v0, 4 # system call code for print_string
la $a0, bye # load address of msg. into $a0
syscall # print the string
li $v0, 10 # terminate program run and
syscall # return control to system
# END OF PROGRAM

Answer 1

If you add two positive numbers together and the result is less than zero, i.e. bit 31 of the result is set, an overflow occurred. If you add two negative numbers together and the result is greater than zero, an overflow occurred. If you add a positive and a negative number, an overflow cannot occur.