mips汇编程序-从字符串中按索引删除字符

Question

I need it for my homework. User inputs a string and index of char he'd like to erase. I should return string without this char and without space. The last thing I've tried it's to copy characters one by one from one string to another and skip the char that I want to delete. Example: received string "asdfghjkl" and I want to delete char No3 so I should print string "asfghjkl" but instead it looks like "ssfggggggggggggggggggggggggggggggggggggggg.......". I tried different combinations and played with counters, tried .space 128 instead of n etc. but with no success. Code runs in QtSpim Thanks

the MIPS code is:

.data
# $s0   str1
# $s7   str2

str1: .space n
str2: .space n
msg1:   .asciiz "Input your string\n\n"
msg2:   .asciiz "\nNumber of character to erase "
err:    .asciiz "error in number"
result: .asciiz "\nthe new string is\n\n"

.text

main:   
    la $a0, str1
add $s0, $a0, $0
la $a0, str2
add $s7, $a0, $0
la $a0, msg1    #Input your string
li $v0, 4
syscall

li $v0, 8   #Read input string to $s0
syscall
move $s0, $a0

la $a0, msg2    #Input your string
li $v0, 4
syscall 

li $v0, 5   #Read Number of character to erase to $s1
syscall
add $s1, $v0, $0    #Number of character to erase $s1==
addi $t0, $s1,-1    #Number of character to erase $t0
addi $t1, $0, 127   #$t1=127 counter

findchar:

ret:
lbu $t5, 0($s0) #copy chars from string1 to string1
sb $t5, 0($s7)

addi $t1, $t1, -1   #counter of whole string1
addi $t0, $t0, -1   #counter of the character we want to erise

addi $s0, $s0, 1    #move to next char
addi $s7, $s0, 1    #move to next char
beqz $t0, shift     #if we at char we want to erise, 
                            #we skip it in string1 and continue
beqz $t1, print     #if string is finished, print result
j findchar



print:  addiu $s7, $s7, -127    #return to first char of new string
la $a0, 0($s7)      #and print it
li $v0, 4
syscall



end:    li $v0, 10
syscall
shift:  addi $s0, $s0, 1    #skip erised char in string1
addi $t1, $t1, -1

j ret           #continue copy chars from string1 to string2

&&&&&&&&&&&&&&&&&&&&

Thank you. After the answer I've changed a code but then the "length" value I get from $a1 is 0x7ffff550. It's my main issue - I'm not succeeding to get the right length.

.data
# $s0   str1
# $s7   str2

    str1: .space n
    str2: .space n
    msg1:   .asciiz "Input your string\n\n"
    msg2:   .asciiz "\nNumber of character to erase "
    err:    .asciiz "error in number"
    result: .asciiz "\nthe new string is\n\n"
.text

main:
    la $a0, str1
    add $s0, $a0, $0
    la $a0, str2
    add $s7, $a0, $0
    la $a0, msg1    #Input your string
    li $v0, 4
    syscall

    li $v0, 8   #Read input string to $s0
    syscall
    move $s0, $a0
    move $s6, $a1

    la $a0, msg2    #Input your Number of character to erase
    li $v0, 4
    syscall 
    li $v0, 5   #Read Number of character to erase to $s1
    syscall
    add $s1, $v0, $0    #Number of character to erase $s1==

    addi $t0, $s1,-1    #Number of character to erase $t0
    add $t1, $s6, $0    #$t1= counter of length

findchar:

ret:
    lb $t5, 0($s0)  #copy chars from string1 to string1
    sb $t5, 0($s7)

    addi $t1, $t1, -1   #counter of whole string1
    addi $t0, $t0, -1   #counter of the character we want to erise

    addi $s0, $s0, 1    #move to next char
    addi $s7, $s0, 1    #move to next char
    beqz $t0, shift     #if we at char we want erise, we skip it in string 1 and continue
    beqz $t1, print     #if string is finished, print result
j findchar

print:  
    la $a0, str2
    #sub $s7, $s7, $s6  #return to first char of new string
    #addi $t1, $t1, -1
    #sub $s7, $s7, $t6
    la $a0, 0($s7)      #and print reult string
    li $v0, 4
    syscall


end:    li $v0, 10
    syscall
shift:  addi $s0, $s0, 1    #skip erised char in string1
    addi $t1, $t1, -1

    j ret           #continue copy chars from string1 to string2

Answer 1

I see a couple of problems with your code.

• The first is that you don't seem to add any NULL terminator to the copied string, which is likely to result in a lot of garbage being printed when you try to print the string.

• The second is that you always loop 127 times, but the input string isn't likely to be 127 characters long. You should stop looping when you reach the end of the input string (the NULL terminator).

• The third is that your implementation would fail if the user wants to remove the very first character, since your skip check is performed after a character has been copied.

Then there's also the issue of unnecessarily complex ways of doing things. I saw a few places in the code where you calculate constant values based on some earlier value, instead of just loading the constant again. For example, addiu $s7, $s7, -127 / la $a0, 0($s7) could have been replaced by a simple la $a0, str2 . This sort of stuff is just going to cause you headaches when your code breaks because it relied on something that no longer is valid because you changed something elsewhere in the code.