實驗目的：熟悉MIPS的指令，掌握簡單的彙編程式結構。

實驗內容：利用系統功能呼叫從鍵盤輸入，轉換後在螢幕上顯示，具體要求如下：

(1) 如果輸入的是字母（A~Z，不區分大小寫）或數字（0~9），則將其轉換成對應的英文單詞後在螢幕上顯示，對應關係見下表

(2) 若輸入的不是字母或數字，則在螢幕上輸出字元“*”

(3) 每輸入一個字元，即時轉換並在螢幕上顯示，需考慮顯示結果的清晰美觀

(4) 支援反覆輸入，直到按？鍵結束程式

(5) 程式結束時，在螢幕上顯示本人的姓名全拼和學號

例：在鍵盤上輸入“PKU2011/”，對應輸出內容為“Papa Kilo Uniform two zero one one *

      .data
alphabet: .asciiz "Alpha ","Bravo ","Charlie ","Delta ","Echo ","Foxtrot ","Golf ","Hotel ","India ","Juliet ","Kilo ","Lima ","Mike ","November ","Oscar ","Papa ","Quebec ","Romeo ","Sierra ","Tango ","Uniform ","Victor ","Whisky ","X-ray ","Yankee ","Zulu "
al_offset: .word 0,7,14,23,30,36,45,51,58,65,73,79,85,91,101,108,114,122,129,137,144,153,161,169,176,184
number: .asciiz "zero ", "one ", "two ", "three ", "four ", "five ", "six ", "seven ","eight ","nine "
n_offset: .word 0,6,11,16,23,29,35,40,47,54 
myname:	.asciiz "\r\nNAME: Wu Yiting\r\n"
myid:	.asciiz "ID: 1200012875\r\n"

      .text
      .globl main
      #? word length[] = 4
main:	li $v0, 12
	syscall
	sub $t1, $v0, 63	# is '?" ?
	beqz $t1, exit
	sub $t1, $v0, 48 	# 0 ascii
	slt $s0, $t1, $0	# if t1 < 0 then s0 = 1
	bnez $s0, others
	
	sub $t2, $t1, 10
	slt $s1, $t2, $0
	bnez $s1, getnum
	
	# is capital?
	sub $t2, $v0, 91
	slt $s3, $t2, $0	# if v0 <= 'Z' then s3 = 1
	sub $t3, $v0, 64	
	sgt $s4, $t3, $0	# if v0 >='A' then s4 = 1
	and $s0, $s3, $s4	# if s3 == 1 && s4 == 1 
	bnez $s0, getword	
	
	# is lower case?
	sub $t2, $v0, 123
	slt $s3, $t2, $0	# if v0 <= 'z' then s3 = 1
	sub $t3,$v0, 96		
	sgt $s4, $t3, $0	# if v0 >= 'a' then s4 = 1
	and $s0, $s3, $s4
	bnez $s0, getword
	j others
	
getnum: add $t2, $t2, 10
	sll $t2, $t2, 2
	la $s0, n_offset
	add $s0, $s0, $t2
	lw $s1, ($s0)
	#sll $s1, $s1, 1
	la $a0, number
	add $a0, $a0, $s1
	li $v0, 4
	syscall
	j main
	
getword:sub $t3, $t3, 1
	sll $t3, $t3,2
	la $s0, al_offset
	add $s0, $s0, $t3
	lw $s1, ($s0)
	#sll $s1, $s1, 1
	la $a0, alphabet
	add $a0, $s1, $a0
	li $v0, 4
	syscall
	j main
	
others:	and $a0, $0, $0
	add $a0, $a0, 42
	li $v0, 11
	syscall
	j main
	
exit:	la $a0, myname
	li $v0, 4
	syscall
	la $a0, myid
	li $v0, 4
	syscall
	li $v0, 1
	syscall

##problem of offset
 

 1、跟x86這題類似採用了二次定址的思想（偏移量是寫程式碼跑出來的=v=, 機器可以做的事情還是懶得數了）

 2、夾逼確定數字以及大小寫

 3、注意.word偏移量*4（這裡‘，’不會影響），而.ascii偏移量*1（尤其坑的是‘，’也算一位，調了很久才發現）