我可以输入数字并显示我输入的数字。 如果我输入 10，我需要添加 1-10 之间的所有偶数和所有奇数

Question

    .equ READERROR, 0 @Used to check for scanf read error. 

     .global main @ Have to use main because of C library uses. 

     main:


     prompt:


@ Ask the user to enter a number.
 
      ldr r0, =strInputPrompt @ Put the address of my string into the first parameter
      bl  printf              @ Call the C printf to display input prompt. 
  
      ldr r0, =numInputPattern @ Setup to read in one number.
      ldr r1, =intInput        @ load r1 with the address of where the
                            @ input value will be stored. 
      bl  scanf                @ scan the keyboard.
      cmp r0, #READERROR       @ Check for a read error.
      beq readerror            @ If there was a read error go handle it. 
      ldr r1, =intInput        @ Have to reload r1 because it gets wiped out. 
      ldr r1, [r1]             @ Read the contents of intInput and store in r1 so that
                            @ it can be printed
      ldr r0, =strOutputNum
      bl  printf

      ldr r0, =strOutputEven

    loop:
      cmp r1, #101 
      beq end 

   
      cmp r1, #0
      bne odd

      cmp r1, #1
      bne even

   

    odd:
    add r1, r1, LSL #1 /* r1 ← r1 + (r1 << 1) */
    bl printf 
    

    even:
    mov r1, r1, ASR #1     /* r1 ← (r1 >> 1) */
    b end_loop

    end_loop:
    add r2, r2, #1         /* r2 ← r2 + 1 */
    b loop                 /* branch to loop */


@ Print the input out as a number.
@ r1 contains the value input to keyboard. 

  
   


     b   myexit @ leave the code. 


     readerror:

@ Got a read error from the scanf routine. Clear out the input buffer then
@ branch back for the user to enter a value. 
@ Since an invalid entry was made we now have to clear out the input buffer by
@ reading with this format %[^\n] which will read the buffer until the user 
@ presses the CR. 

     ldr r0, =strInputPattern
     ldr r1, =strInputError   @ Put address into r1 for read.
     bl scanf                 @ scan the keyboard.

  

不会对输入做任何事情。 这只是清理输入缓冲区。 输入缓冲区现在应该是清空的，以便获得另一个输入。

    b prompt


    myexit:

我的代码结束。 强制退出并将控制权返回给操作系统

    mov r7, #0x01 @ SVC call to exit
    svc 0         @ Make the system call. 

    .data

声明所需的字符串和数据

    .balign 4
    strInputPrompt: .asciz "Input a number between 1 and 100: \n"

    .balign 4
    strOutputNum: .asciz "You entered: %d \n"

    .balign 4
    strOutputEven: .asciz "The even numbers from 1 to %d are: \n"

scanf 调用的格式模式。

    .balign 4
    numInputPattern: .asciz "%d"  @ integer format for read. 

    .balign 4
    strInputPattern: .asciz "%[^\n]" @ Used to clear the input buffer for invalid input. 

    .balign 4
    strInputError: .skip 100*4  @ User to clear the input buffer for invalid input. 

    .balign 4
    intInput: .word 0   @ Location used to store the user input. 

    .global printf

    .global scanf

无法使偶数和奇数函数工作

Answer 1

第一个问题在这里：

  cmp r1, #0
  bne odd

  cmp r1, #1
  bne even

当您只需要最右边的位时，这实际上将整个数字与 0 或 1 进行比较。 你需要做这样的事情。 我只会列出偶数的情况，我想你可以找出奇数。 我在 ARM 组装方面有点生疏，还没有测试过这个，但它应该可以工作：

tst r1,#1  @ sets the flags as you did "AND r1,r1,#1" but doesn't change r1
bne odd    @ now you will jump to label "odd" if r1 is odd, or keep going if it's even.

@ if it isn't odd, it must be even, so your even code goes here!

push r1-r2   @ technically this is a thumb mode only instruction but if your assembler allows
             @ unified syntax it should get assembled as the correct "STMFD sp!,{r1-r2}"
             @ this saves r1 and r2 on the stack, we get them back with POP.
             @ C functions assume the stack is aligned to 8 bytes so we have to push an 
             @ even number of registers even though we only needed to push R1.

    ldr r0,=strOutputEven   @ r1 still contains intInput
    bl printf               @prints "The even numbers from 1 to %d are,"
pop R1-R2                   @unified syntax for "LDMFD sp!,{r1-r2}"

@ now we'll do the loop:

ldr r0,=numInputPattern
mov r1,#0                   @ we don't need the input anymore
mov r2,#0                   @ the sum goes here

loop_even:
add r1,r1,#2               
cmp r1,#101
bcc exitLoop               @ if R1 is greater than or equal to 101, exit.
PUSH R0-R12                @ I can't remember what printf alters so better safe than sorry.
bl printf
POP R0-R12
add r2,r2,r1               @ add R1 to R2 and store the result in R2.
b loop_even
exitloop:
mov r1,r2                  @put the sum into r1 so we can print it
bl printf

b my_exit

odd: