c - 输出不会在某个值之后出现

Question

这个问题已经有答案了:

Binary to decimal conversion C code - Problem in satisfying particular test cases (2 个回答)

已关闭 3 年前。

下面编写的代码将十进制转换为二进制。该代码在 1009 之前给出正确的输出。之后，它给出错误的输出。为什么这样？int 保证至少能够存储 -32767 到 32767 范围内的值。

 #include<stdio.h>

int main() {
  int remainder, n = 0;
  long binary = 0;
  int i = 1;
  scanf("%d",&n);
  while (n != 0) 
  {
    remainder = n % 2;

    binary = binary + remainder * i;
    i = i * 10;

    n = n / 2;
  }

  printf("%ld", binary);  // Be sure to use "%ld" with `long`.
  return 0;
}

示例运行:

INPUT:  1100
OUTPUT: 1411066508

Answer 1

After that onwards it gives wrong output. Why so?

以下 2 个中的任何一个溢出。值远超过 32767。

binary=binary+remainder*i;
i=i*10;

尝试使用此代码进行演示。

printf("before: binary %ld, remainder %d, i  %d\n", binary, remainder, i);
binary=binary+remainder*i;
i=i*10;
printf("after:  binary %ld, remainder %d, i  %d\n", binary, remainder, i);

请注意，一旦发生有符号整数溢出，那就是未定义的行为并且任何事情都可能发生。

<小时/>

#include<stdio.h>

int main() {
  int remainder, n = 0;
  long int binary = 0;
  int i = 1;
  n = 1010;
  while (n != 0) {
    remainder = n % 2;
    printf("before: binary %10ld, remainder %d, i  %10d\n", binary, remainder, i);
    binary = binary + remainder * i;
    i = i * 10;
    printf("after:  binary %10ld, remainder %d, i  %10d\n", binary, remainder, i);
    n = n / 2;
  }
  printf("%ld", binary);  // Be sure to use "%ld" with `long`.
  return 0;
}

输出

before: binary          0, remainder 0, i           1
after:  binary          0, remainder 0, i          10
before: binary          0, remainder 1, i          10
after:  binary         10, remainder 1, i         100
before: binary         10, remainder 0, i         100
after:  binary         10, remainder 0, i        1000
before: binary         10, remainder 0, i        1000
after:  binary         10, remainder 0, i       10000
before: binary         10, remainder 1, i       10000
after:  binary      10010, remainder 1, i      100000
before: binary      10010, remainder 1, i      100000
after:  binary     110010, remainder 1, i     1000000
before: binary     110010, remainder 1, i     1000000
after:  binary    1110010, remainder 1, i    10000000
before: binary    1110010, remainder 1, i    10000000
after:  binary   11110010, remainder 1, i   100000000
before: binary   11110010, remainder 1, i   100000000
after:  binary  111110010, remainder 1, i  1000000000
before: binary  111110010, remainder 1, i  1000000000
after:  binary 1111110010, remainder 1, i  1410065408
1111110010

当 i 变为 10,000,000,000 时，其值将超过 INT_MAX。