C++程序Booths Algorithm 2s Complement using array

Question

我已经包含了我在其中遇到逻辑问题的程序。该程序基于 booth 的算法，我已经放了一个片段。在这个 'working' 片段中，十进制数从用户那里接受，借助数组 (a[0]=1 LSB) 转换为十进制形式，最后计算数组 b[] 的 2s 补码。现在，当我运行程序时：

    #include<iostream>
    using namespace std;
    class booth
    {
    public:
    int n;
    int b[3];
    int comb[3], q[3];              //b=multiplicand q=multiplier
    int bb, qq;                     //bb and qq store actual decimal no.s    
    booth()
    {
        for(int i=0; i<4; i++)
        {
            b[i]=0;                 //b array stores multiplicand in binary
            q[i]=0;                 //q array stores multiplier in binary
            comb[i]=0;              //will store calculated 2s complement in      
                                      binary
        }
        n=4;
        bb=0;
        qq=0;
    }
void acceptMm();
void display();
};

void booth :: acceptMm()     //function to accept value from user and                     
                             //converting it into binary in the form of 
                             //array and then calculating its 2s complement
{
    cout<<"Enter Multiplicand: ";
    cin>>bb;
    cout<<"Enter Multiplier: ";
    cin>>qq;
    //decimal to binary
    int rem1, rem2, i=0, j=0; //rem1 and rem2 are remainders
    while(qq!=0)
    {
        rem2=qq%2;
        qq/=2;
        q[i]=rem2;
        i++;
    }
    cout<<q[3]<<q[2]<<q[1]<<q[0]<<endl;  // to display binary no.
    //again decimal to binary
    while(bb!=0)
    {
        rem1=bb%2;
        bb/=2;
        b[j]=rem1;
        j++;
    }
    cout<<b[3]<<b[2]<<b[1]<<b[0]<<endl;  //to display binary no.
    // 2s complement:
    int ii=0;
    int jj=4;    //4 bit binary number
        while(b[ii]==0 && jj!=0)
        {
            comb[ii]=b[ii];
            ii++;
            jj--;
        }
        comb[ii]=b[ii];
        cout<<b[3]<<b[2]<<b[1]<<b[0]<<endl;   //displayed value (problem)
        ii++;
        jj--;
        if(jj==0)
        {
            return;
        }
        while(jj!=0)
        {
        if(b[ii]==0)
        {
            comb[ii]=1;
            ii++;
            jj--;   }
        else
        {
            comb[ii]=0;
            ii++;
            jj--;
        }
        }
}

void booth :: display()
{
    cout<<"multiplicand\n";
    for(int x=3; x>=0; x--)
        {
            cout<<b[x]<<" ";
        }
    cout<<endl;
    cout<<"multiplier\n";
    for(int j=3; j>(-1); j--)
    {
        cout<<q[j]<<" ";
    }
    cout<<endl;
    cout<<"compliment of multiplicand\n";
    for(int y=3; y>(-1); y--)
    {
        cout<<comb[y]<<" ";
    }
}

int main()
{
booth obj;
cout<<"Booths Algorithm\n";
    obj.acceptMm();
    obj.display();
return 0;
}

Output

Booths Algorithm
Enter Multiplicand: 5
Enter Multiplier: 4
0100
0101
1101
multiplicand
1 1 0 1 
multiplier
0 1 0 0 
compliment of multiplicand
0 0 1 1

在输出中，我希望第 6 行为 0101，但得到的是 1101。为什么数组 b[] 的值会发生变化？第 5 行的数组 b[] 的值是正确的，为什么它会改变？根据代码，该值不应该改变，对吗？我卡住了..请帮忙！！任何建议将不胜感激！！

Answer 1

b、q 和 comb 是 3 个元素的数组，因此 b[3] 是数组溢出（其值未知）。事实上 comb 在 b 之后分配，很可能 b[3] 等于 comb[0].

Answer 2

您正在溢出。像这样做。简单.

class booth {
public:
    int n;
    int b[4];
    int comb[4], q[4];              //b=multiplicand q=multiplier
    int bb, qq;                     //bb and qq store actual decimal no.s
    booth() {
        for (int i = 0; i < 4; i++) {
            b[i] = 0;                 //b array stores multiplicand in binary
            q[i] = 0;                 //q array stores multiplier in binary
            comb[i] = 0;       //will store calculated 2s complement in        }
            n = 4;
            bb = 0;
            qq = 0;
        }
    }

C++程序Booths Algorithm 2s Complement using array

C++ program Booths Algorithm 2s Complement using array

c++

arrays

complement