How to print a minus (-) whenever a double consonant occurs in a string through Assembly (RISC-V)?

Question

I have a program exercise that need assistance with. This program was created through RARS 1.3. So far, this is the code I created to read and input one string at a time. The program needs to put a (-) between all double consonants in the string. To do this, I would need to loop through the string to search for double consonants and have a second string to print the result in. Any suggestions?

.global _start      # Provide program starting address to linker

_start: 
   la t1,sourcestring
   li t2,10 #enter
   loop:
   addi a7,x0,12 #readchar
   ecall
   # input is in a0
   sb a0,0(t1)
   addi t1,t1,1
   bne a0,t2,loop
   sb x0,0(t1)
   
.data
sourcestring:      .word 30 #30
targetstring:      .word 40 #40

Answer 1

There is a little modification of your code.

    .global _start      # Provide program starting address to linker

_start: 
    la t1,sourcestring
    li t2,10 #enter
    li t3,65 #A
    li t4,45 #-
    li t5,0xffff #initilaize t5 to something readchar is not supposed to return.
    j label1
loop:
    mv t5,a0 #put old a0 value in t5
label1: 
    addi a7,x0,12 #readchar
    ecall
    # input is in a0
    sb a0,0(t1)
    addi t1,t1,1
    beq a0,t3,loop
    bne a0,t5,label2 #if a0 is different from old a0 value dont add -
    sb  t4,0(t1)
    addi t1,t1,1
label2: 
    bne a0,t2,loop
    sb x0,0(t1)
   
    .data   
sourcestring:      .word 30 #30
targetstring:      .word 40 #40

In this example if we found two times the same char (except A) we add -. and the modification is made directly in sourcestring. If you want you can modify it to write in targetstring.

Be careful, tagetstring and sourcesring are only one word in your example (4 bytes), depending on your string you can exceed this size and overwrite data that you did not want to overwrite.

Good luck with your modifications.