c - 二进制打印在 C 中不起作用

Question

我正在尝试使用 c 中的 32 位位掩码打印二进制，但二进制表示没有在 if 语句中打印。

unsigned int bit_mask = 2147483648;
int decimal = 2;
printf("\nBinary representation of 2: \n");
while(bit_mask > 0){
    if((decimal & bit_mask) == 0)
        printf("0");
    else
        printf("1");
    bit_mask = bit_mask >> 1;
}

decimal = 255;
printf("\n\nBinary representation of 255: \n");
while(bit_mask > 0){
    if((decimal & bit_mask) == 0)
        printf("0");
    else
        printf("1");
    bit_mask = bit_mask >> 1;
}

decimal = 32;
printf("\n\nBinary representation of 32: \n");
while(bit_mask > 0){
    if((decimal & bit_mask) == 0)
        printf("0");
    else
        printf("1");
    bit_mask = bit_mask >> 1;
}

decimal = -1;
printf("\n\nBinary representation of -1: \n");
while(bit_mask > 0){
    if((decimal & bit_mask) == 0)
        printf("0");
    else
        printf("1");
    bit_mask = bit_mask >> 1;
}

decimal = -255;
printf("\n\nBinary representation of -255: \n");
while(bit_mask > 0){
    if((decimal & bit_mask) == 0)
        printf("0");
    else
        printf("1");
    bit_mask = bit_mask >> 1;
}

int random_number =  (rand() % INT_MAX) + (rand() % INT_MIN);
printf("\n\nBinary representation of %d: \n", random_number);
while(bit_mask > 0){
    if((random_number & bit_mask) == 0)
        printf("0");
    else
        printf("1");
    bit_mask = bit_mask >> 1;
}

PS:该程序现在仅适用于 2，但仍未打印其他值(255、32、-1、-255)

Answer 1

如果按照 BLUEPIXY 和我自己的建议进行修正，代码将生成位序列正确的答案。

#include <stdio.h>

int main(void)
{
    for (unsigned value = 2; value < 1024; value = value * 3 + 1)
    {
        unsigned bit_mask = 0x80000000;  // 2147483648

        printf("Binary representation of %3u: ", value);
        while (bit_mask > 0)
        {
            if ((value & bit_mask) == 0)
                printf("0");
            else
                printf("1");
            bit_mask >>= 1;
        }
        putchar('\n');
    }
    return 0;
}

输出:

Binary representation of   2: 00000000000000000000000000000010
Binary representation of   7: 00000000000000000000000000000111
Binary representation of  22: 00000000000000000000000000010110
Binary representation of  67: 00000000000000000000000001000011
Binary representation of 202: 00000000000000000000000011001010
Binary representation of 607: 00000000000000000000001001011111

不管BLUEPIXY如何，输出都没有反转在 comments 中说.

---

循环体可以被转换成一个函数，例如 void print_binary(unsigned value) 以最小的努力，然后从循环中调用它。带有或多或少相同循环的编辑问题被写了六次(!) 是一种讽刺——不要写那样的代码。当您像那样复制'n'粘贴代码时，就会有一个函数等待编写。

#include <stdio.h>

void print_binary(unsigned value)
{
    unsigned bit_mask = 0x80000000;  // 2147483648

    while (bit_mask > 0)
    {
        if ((value & bit_mask) == 0)
            printf("0");
        else
            printf("1");
        bit_mask >>= 1;
    }
}

此函数可用于打印 unsigned int 的二进制表示而不添加任何修饰。一般都能合理使用。在这个特定的上下文中，您可以编写一个包装函数处理其他格式:

void fmt_binary(int value)
{
    printf("Binary representation of %3d: ", value);
    print_binary((unsigned)value);
    putchar('\n');
}

只要范围内有 print_binary() 的原型(prototype)，就不需要强制转换。从 C99 开始，您必须有一个函数声明，但不一定是原型(prototype)。然而，在没有原型(prototype)的情况下进行编译是愚蠢的。你应该找到确保你的编译器在你试图跳过时提示的选项。对于 GCC，您可以使用:

gcc -std=c11 -O3 -g -Wall -Wextra -Werror -Wmissing-prototypes -Wstrict-prototypes …

您可能会或可能不会添加 -Wold-style-declaration 或 -Wold-style-definition 取决于您处理的代码库和您正在使用 GCC(以及您在编写代码时有多粗心)。您还可以考虑其他选项，例如 -Wshadow，但如果您的代码可以按照显示的内容进行干净地编译，则不太可能遇到许多不是逻辑问题的问题。

定义了fmt_binary()，你可以这样写main():

#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

// … declarations or definitions of fmt_binary and print_binary

int main(void)
{
    for (int value = 2; value < 1024; value = value * 3 + 1)
        fmt_binary(value);
    fmt_binary(2);
    fmt_binary(255);
    fmt_binary(32);
    fmt_binary(-1);
    fmt_binary(-255);
    srand(time(0));     // Better than no call to srand()
    int random_number =  (rand() % INT_MAX) + (rand() % INT_MIN);
    fmt_binary(random_number);
    return 0;
}

示例输出可能是:

Binary representation of   2: 00000000000000000000000000000010
Binary representation of   7: 00000000000000000000000000000111
Binary representation of  22: 00000000000000000000000000010110
Binary representation of  67: 00000000000000000000000001000011
Binary representation of 202: 00000000000000000000000011001010
Binary representation of 607: 00000000000000000000001001011111
Binary representation of   2: 00000000000000000000000000000010
Binary representation of 255: 00000000000000000000000011111111
Binary representation of  32: 00000000000000000000000000100000
Binary representation of  -1: 11111111111111111111111111111111
Binary representation of -255: 11111111111111111111111100000001
Binary representation of -1758826555: 10010111001010100110111111000101