所以我现在正在做一个项目，我们必须接受一个字符串并将其转换为所有大写字母，然后如果 toUpper 或 toLower 字节不是 0，则转换为小写字母。现在我仍在处理大写字母部分（猜测小写字母几乎相同），但是当我遍历字符串查找大写字母时或者当我调用系统调用进行打印时，我遇到了困难。任何帮助都会很棒。这是我到目前为止所拥有的：
.data
toUpper: .byte 1
toLower: .byte 0
string:
.asciiz " A long time ago in a Galaxy far, far away...."
# Your code goes below this line
origString:
.asciiz "Original string:\n"
toUpForwardStr:
.asciiz "\nConverted to upper-case:\nForward:\n"
toLowerForwardStr:
.asciiz "\nConverted to lower-case:\nForward:\n"
backwardStr:
.asciiz "Backward:"
.text
main:
# Function prologue
subu $sp, $sp, 24 # allocate stack space -- default of 24 here
sw $fp, 0($sp) # save caller's frame pointer
sw $ra, 4($sp) # save return address
addiu $fp, $sp, 20 # setup main's frame pointer
la $a0, origString #Print "Original String:"
addi $v0, $zero, 4
syscall
la $a0, string #Print string
addi $v0, $zero, 4
syscall
la $s0, toUpper
sb $s1, 0($s0) #toUpper stored in $s1
la $s0, toLower
sb $s2, 0($s0) #toLower stored in $s2
bne $s1, $zero, toUpperCase #Jump toUpperCase if toUpper ≠ 0
toUpperCase:
la $a0, toUpForwardStr #Print "Converted to upper-case:"
addi $v0, $zero, 4 # "Forward:"
syscall
la $s3, string #$s3 holds address to string
addi $s1, $zero, 0 #$s1 = i = 0
j upperCaseLoop #Goto upperCaseLoop
upperCaseLoop:
# Compute address of string[i]
add $t2, $s3, $s1 # $t2 = address of string[i]
lb $t3, 8($t2) # $t3 = elements[i]
beq $t3, $zero, upperDone # test if for loop is done
addi $t6, $zero, 96 #$t6 = 96 (lowercase letters)
bgt $t3, $t6, isLowercase1#If letter is lowercase goto isLowercase1
comeBackFromLowercaseIfs:
move $t3, $a0
addi $v0, $zero, 11
syscall
addi $s1, $s1, 1 # i++
j upperCaseLoop
upperDone:
bne $s2, $zero, toLowerCase #Jump toLowerCase if toLower ≠ 0
toLowerCase:
la $a0, toLowerForwardStr #Print "Converted to lower-case:"
addi $v0, $zero, 4 # "Forward:"
syscall
j done #The END!!
isLowercase1:
addi $t7, $zero, 123 #$t7 = 123
blt $t3, $t7, isLowercase2 #Goto isLowercase2
j comeBackFromLowercaseIfs #Go back to uppercaseLoop
isLowercase2:
addi $t3, $zero, -30 #changes letter to lowercase
j comeBackFromLowercaseIfs #Go back to uppercaseLoop
done:
# Epilogue for main -- restore stack & frame pointers and return
lw $ra, 4($sp) # get return address from stack
lw $fp, 0($sp) # restore the caller's frame pointer
addiu $sp, $sp, 24 # restore the caller's stack pointer
jr $ra # return to caller's code
