第2章 编程问题 2.2节 3

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第2章 编程问题 2.2节 3

编写一个程序，读取包含一个位运算符的输入行——&、|、^、<<或>>，位运算符的后面跟着整数操作数，接着输出这些整数操作数、位运算符以及将位运算符应用到操作数所得的结果。将这些数字同时以十进制形式和32位的二进制形式显示，使用问题1中的printBinary()函数。例如，输入
& 13 27
将产生输出
Applying the bitwise AND operator & to the following
13 = 0000 0000 0000 0000 0000 0000 0000 1101
27 = 0000 0000 0000 0000 0000 0000 0001 1011
produces
9 = 0000 0000 0000 0000 0000 0000 0000 1001
而输入
~ 1
产生输出
Applying the bitwise NOT operator ~ to the following
1 = 0000 0000 0000 0000 0000 0000 0000 0001
produces
-2 = 1111 1111 1111 1111 1111 1111 1111 1110
注意：实际输出二进制形式时没有空格，这里是为了让各位看清位数

C++实现：

#include <iostream>
using namespace std;

void printBinary(int value);
void bitOperation();

void main() {
    bitOperation();
    system("pause");
}

void bitOperation() {
    char operate_text[][11] = { "NOT", "AND", "OR", "XOR", "LEFTSHIFT", "RIGHTSHIFT" };
    int index = 0;//每个操作符所对应的文本描述在数组中的序号（以0开始）
    char operate[100] = { 0 };//操作符，申请了一块较长的内存，防止用户的非法输入
    int operand1, operand2;//两个操作数
    int result = 0;//操作数运算的结果

    cin >> operate;
    if (strcmp(operate,"~") == 0) {//用strcmp函数判断用户输入的操作符是否合法
        cin >> operand1;
        index = 0;
        result = ~operand1;
    }
    else {
        cin >> operand1 >> operand2;
        if (strcmp(operate, "&") == 0) {
            index = 1;
            result = operand1 & operand2;
        }
        else if (strcmp(operate, "|") == 0) {
            index = 2;
            result = operand1 | operand2;
        }
        else if (strcmp(operate, "^") == 0) {
            index = 3;
            result = operand1 ^ operand2;
        }
        else if (strcmp(operate, "<<") == 0) {
            index = 4;
            result = operand1 << operand2;
        }
        else if (strcmp(operate, ">>") == 0) {
            index = 5;
            result = operand1 >> operand2;
        }
        else {//如果用户输入的操作符不是位运算符，将输出错误提示
            cout << "INPUT ERROR!" << endl;
            cout << "The operator " << "\"" << operate << "\"" << " is invalid." << endl;
            return;
        }
    }

    cout << "Applying the bitwise " << operate_text[index] << " operator " << operate << " to the follwing" << endl;
    cout << "\t" << operand1 << " = ";
    printBinary(operand1);
    cout << endl;
    if (index != 0) {
        cout << "\t" << operand2 << " = ";
        printBinary(operand2);
        cout << endl;
    }
    cout << "produces" << endl;
    cout << "\t" << result << " = ";
    printBinary(result);
    cout << endl;
}

//这是上一篇中使用的函数，这里用来输出操作数和运算结果的二进制形式
void printBinary(int value) {
    int bitOfBinary = sizeof(value) * 8;//sieof运算符获取value占几个字节，一个字节是8位
    unsigned int mask = 1 << (bitOfBinary - 1);//假设bitOfBinary是32，将1左移31位得到10000000000000000000000000000000
    for (int i = 1; i <= bitOfBinary; i++) {
        int temp = mask & value;
        if (temp == 0) {
            cout << 0;
        }
        else {
            cout << 1;
        }
        mask >>= 1;//每次将mask右移一位
    }
}