我正在尝试运行程序，但它给了我这个错误“第48行：0x00400088处的运行时异常：地址超出范围0x00000000”
toUpperCase:
bgt $t5, $s2, exit_toUpperCase
lb $t1, ($t5) # address out of range in this line
add $t5, $t5, 1
bgt $t1, 96, check_ASCII_number
j toUpperCase