[英]integer type long and division
I just write a procedure to decompose an unsigned integer to prime numbers. 我只是编写了将无符号整数分解为素数的过程。 it will work normally if I define the data type as " int ", if I change it to " long ", result will be wrong.
如果将数据类型定义为“ int ”,它将正常工作;如果将其更改为“ long ”,则结果将是错误的。 I don't know why.
我不知道为什么
BTW, I used Win-TC as my compiler. 顺便说一句,我使用Win-TC作为编译器。
Code as below: 代码如下:
#include "stdio.h"
#define True 0xff
#define False 0x00
char DividerIsPrime(unsigned long data);
void CheckIfDataCanBeExtracted(unsigned long data);
main()
{
unsigned long data;
printf("please input data:");
scanf("%d",&data);
printf("\n%d=",data);
CheckIfDataCanBeExtracted(data);
// printf("%d",sizeof(short));
getch();
}
void CheckIfDataCanBeExtracted(unsigned long data)
{
unsigned long divider,temp,data1;
data1=data;
for(divider=2;divider<=data;divider++)
{
temp=data1%divider;
if(temp) {continue; }
if(DividerIsPrime(divider)) {
data1 = data1/divider;
printf("%d",divider);
if(data1==1) break;
else {printf("*"); divider--;}
}
}
return;
}
/* Check if this number is a prime number */
char DividerIsPrime(unsigned long data)
{
unsigned long divider;
char status=True;
for(divider=2;divider<data;divider++)
{
if(data%divider) status=True;
else status=False;
}
return status;
}
Thanks for Paul's help, I know where is wrong. 感谢保罗的帮助,我知道哪里出了问题。 %d should be replaced by %ld.
应将%d替换为%ld。
Your function DividerIsPrime
,as currently written, has the defect that logically it must always return True
. 当前编写的函数
DividerIsPrime
具有逻辑上必须始终返回True
的缺陷。
The reason for this is that status is changed at each iteration. 原因是状态在每次迭代时都会更改。 Even if
status=False
is reached (the number is composite because the modulus came out zero for a divider), then the iterations will continue and in every case, status=True
will be reached on the final iteration when divider == (data - 1) . 即使达到
status=False
(数字是复合的,因为除法器的模数为零),迭代仍将继续,并且在每种情况下,当除法器==时,最终迭代将达到status=True
(数据- 1) 。
You can change this as follows: 您可以如下更改:
/* Check if this number is a prime number */
char DividerIsPrime(unsigned long data)
{
unsigned long divider;
for(divider=2;divider<data;divider++)
{
if (0==(data % divider))
return False;
}
return True;
}
You would have found this with some "unit test" such as: 您将通过一些“单元测试”找到它,例如:
assert(DividerIsPrime(5));
assert(!DividerIsPrime(6)); /* This test would fail without corrected code. */
Obviously there are much more efficient algorithms for "primality testing". 显然,有更有效的“素数测试”算法。
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