匯編語言-求X的階乘

1. 題目：求X的階乘值

2. 要求：輸入一個整型數（不超過10），求出其階乘值后輸出，求階乘的算法用子程序來實現。

3. 提示：可以用遞歸來實現，也可以用簡單的循環來實現。

這里使用循環來實現：

對於匯編新手，最好通過高級語言的編程測試，然后再寫匯編代碼，這樣效果會好一些、

求階乘的C++代碼如下：

//The program is to find the factorial from 1 to 10
//author:Karllen
//Date:  05/21/2014

#include <iostream>

int factorial(int n);

int main()
{
    int n;
    std::cin>>n;
    std::cout<<factorial(n)<<std::endl;

    system("pause");
    return 0;
}

int factorial(int n)
{
    int sum = 1;
    while (n!=1)
    {
        sum*=n;
        --n;
    }
    return sum;
}

匯編代碼如下：

; Example assembly language program -- adds two numbers
; Author:  Karllen
; Date:    revised 05/2014

.386
.MODEL FLAT

ExitProcess PROTO NEAR32 stdcall, dwExitCode:DWORD

INCLUDE io.h            ; header file for input/output

cr      EQU     0dh     ; carriage return character
Lf      EQU     0ah     ; line feed

.STACK  4096            ; reserve 4096-byte stack
        
.DATA                   ; reserve storage for data
        prompt   BYTE "The program is to find the factorial from 1 to 10",cr,Lf,0
        numInput BYTE "Please enter a number from 1 to 10",cr,Lf,0
        answer   BYTE "The number factorial is"
        value    BYTE 11 DUP(?)
                 BYTE cr,Lf,0

PUBLIC _start         
.CODE 
_start:
                                ; start of main program code
        output prompt 
        
        doInput:
           output numInput
           input  value,11
           atod   value
           cmp    eax,1
           jl     doInput
           cmp    eax,10
           jg     doInput
        push   eax
        call   findFactorial
        add    esp,4
        
        dtoa   value,eax
        output answer 
        
        INVOKE  ExitProcess, 0  ; exit with return code 0
                  ; make entry point public
        
 findFactorial  PROC NEAR32
                  push ebp
                  mov  ebp,esp
                  
                  mov  eax,[ebp+8]
                  mov  ebx,eax
                  cmp  eax,1
                  je   endFindWhile     
                  doFindWhile:
                           dec ebx
                           cmp ebx,1
                           je  endFindWhile
                           mul ebx
                           jmp doFindWhile
                  endFindWhile:          
                  pop  ebp
                  ret
   findFactorial  ENDP
END                             ; end of source code

測試結果：