第一題：用系統功能調用實現簡單輸入輸出
利用系統功能調用從鍵盤輸入，轉換後在屏幕上顯示，具體要求如下：
(1) 如果輸入的是字母（A~Z，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屏幕上顯示，對應關係見下表
(2) 若輸入的不是字母或數字，則在屏幕上輸出字符“*”，
(3) 每輸入一個字符，即時轉換並在屏幕上顯示，
(4) 支持反覆輸入，直到按“?”鍵結束程序。
.data
u_word: .asciiz
"Alpha ","Bravo ","China ","Delta ","Echo ","Foxtrot ",
"Golf ","Hotel ","India ","Juliet ","Kilo ","Lima ",
"Mary ","November ","Oscar ","Paper ","Quebec ","Research ",
"Sierra ","Tango ","Uniform ","Victor ","Whisky ","X-ray ",
"Yankee ","Zulu "
uw_offset: .word
0,7,14,21,28,34,43,49,56,63,71,
77,83,89,99,106,113,121,131,
139,146,155,163,171,178,186
l_word: .asciiz
"alpha ","bravo ","china ","delta ","echo ","foxtrot ",
"golf ","hotel ","india ","juliet ","kilo ","lima ",
"mary ","november ","oscar ","paper ","quebec ","research ",
"sierra ","tango ","uniform ","victor ","whisky ","x-ray ",
"yankee ","zulu "
lw_offset: .word
0,7,14,21,28,34,43,49,56,63,71,
77,83,89,99,106,113,121,131,
139,146,155,163,171,178,186
number: .asciiz
"zero ", "First ", "Second ", "Third ", "Fourth ",
"Fifth ", "Sixth ", "Seventh ","Eighth ","Ninth "
n_offset: .word
0,6,13,21,28,36,43,50,59,67
.text
.globl main
main: li $v0, 12 # read character
syscall
sub $t1, $v0, 63 # '?'
beqz $t1, exit
sub $t1, $v0, 48 # '0'
slt $s0, $t1, $0 # if t1 < 0 then s0 = 1
bnez $s0, others
# is number?
sub $t2, $t1, 10 # number
slt $s1, $t2, $0 # if t2 < 0 then s1 = 1
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, getuword
# 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, getlword
j others
getnum: add $t2, $t2, 10
sll $t2, $t2, 2
la $s0, n_offset
add $s0, $s0, $t2
lw $s1, ($s0)
la $a0, number
add $a0, $a0, $s1
li $v0, 4
syscall
j main
# upper case word
getuword: sub $t3, $t3, 1
sll $t3, $t3, 2
la $s0, uw_offset
add $s0, $s0, $t3
lw $s1, ($s0)
la $a0, u_word
add $a0, $s1, $a0
li $v0, 4
syscall
j main
# lower case word
getlword: sub $t3, $t3, 1
sll $t3, $t3, 2
la $s0, lw_offset
add $s0, $s0, $t3
lw $s1, ($s0)
la $a0, l_word
add $a0, $s1, $a0
li $v0, 4
syscall
j main
others: and $a0, $0, $0
add $a0, $a0, 42 # '*'
li $v0, 11 # print character
syscall
j main
exit: li $v0, 10 # exit
syscall第二題：字符串查找比較
利用系統功能調用從鍵盤輸入一個字符串，然後輸入單個字符，查找該字符串中是否有該字符（區分大小寫）。具體要求如下：
(1) 如果找到，則在屏幕上顯示：
Success! Location: X
其中，X爲該字符在字符串中第一次出現的位置
(2) 如果沒找到，則在屏幕上顯示：
Fail!
(3) 輸入一個字符串後，可以反覆輸入希望查詢的字符，直到按“?”鍵結束程序
(4) 每個輸入字符獨佔一行，輸出查找結果獨佔一行，位置編碼從1開始。
提示：爲避免歧義，字符串內不包含"?"符號
格式示例如下：
abcdefgh
a
Success! Location: 1
x
Fail!
.data
msg_s: .asciiz "\r\nSuccess! Location: "
msg_f: .asciiz "\r\nFail!\r\n"
s_end: .asciiz "\r\n"
buf: .space 100
.text
.globl main
main: la $a0, buf # address of input buffer
la $a1, 100 # maximum number of characters to read
li $v0, 8 # read string
syscall
inputchar: li $v0, 12 # read character
syscall
addi $t7, $0, 63 # '?'
sub $t6, $t7, $v0
beq $t6, $0, exit
add $t0, $0, $0
la $s1, buf
find_loop: lb $s0, 0($s1)
sub $t1, $v0, $s0
beq $t1, $0, success
addi $t0, $t0, 1
slt $t3, $t0, $a1
beq $t3, $0, fail
addi $s1 $s1, 1
j find_loop
success: la $a0, msg_s
li $v0, 4 # print string
syscall
addi $a0, $t0, 1
li $v0, 1 # print integer
syscall
la $a0, s_end
li $v0, 4
syscall
j inputchar
fail: la $a0, msg_f
li $v0, 4
syscall
j inputchar
exit: li $v0, 10
syscall