[英]conversion from any base to base 10 c++
I found two ways of conversion from any base to base 10 . 我发现从任何基数到10的两种转换方式。 the first one is the normal one we do in colleges like 521(base-15) ---> (5*15^2)+(2*15^1)+(1*15^0)=1125+30+1 = 1156 (base-10) .
第一个是我们在大学里像521(base-15)这样的普通人--->(5 * 15 ^ 2)+(2 * 15 ^ 1)+(1 * 15 ^ 0)= 1125 + 30 + 1 = 1156(以10为基)。 my problem is that i applied both methods to a number (1023456789ABCDE(Base-15)) but i am getting different result .
我的问题是我将这两种方法都应用于一个数字(1023456789ABCDE(Base-15)),但结果却有所不同。 google code jam accepts the value generated from second method only for this particular number (ie 1023456789ABCDE(Base-15)) .
google code jam仅接受该特定数字(即1023456789ABCDE(Base-15))从第二种方法生成的值。 for all other cases both generates same results .
对于其他所有情况都产生相同的结果。 whats big deal with this special number ??
这个特殊号码有什么大不了的? can anybody suggest ...
有人可以建议...
#include <iostream>
#include <math.h>
using namespace std;
int main()
{ //number in base 15 is 1023456789ABCDE
int value[15]={1,0,2,3,4,5,6,7,8,9,10,11,12,13,14};
int base =15;
unsigned long long sum=0;
for (int i=0;i<15;i++)
{
sum+=(pow(base,i)*value[14-i]);
}
cout << sum << endl;
//this prints 29480883458974408
sum=0;
for (int i=0;i<15;i++)
{
sum=(sum*base)+value[i];
}
cout << sum << endl;
//this prints 29480883458974409
return 0;
}
Consider using std::stol
( ref ) to convert a string into a long. 考虑使用
std::stol
( ref )将字符串转换为long。 It let you choose the base to use, here an example for your number wiuth base 15
. 它允许您选择要使用的基数,这里是使用基数
15
的示例。
int main()
{
std::string s = "1023456789ABCDE";
long n = std::stol(s,0,15);
std::cout<< s<<" in base 15: "<<n<<std::endl;
// -> 1023456789ABCDE in base 15: 29480883458974409
}
pow(base, i)
使用浮点数,因此您会降低某些数字的精度。
Exceeded double
precision. 超过
double
精度。
Precision of double
, the return value from pow()
, is precise for at least DBL_DIG
significant decimal digits. double
精度,即pow()
的返回值,至少对于DBL_DIG
有效的十进制数字是精确的。 DBL_DIG
is at least 10 and typically is 15 IEEE 754 double-precision binary . DBL_DIG
至少为 10,通常为15 IEEE 754双精度二进制文件 。
The desired number 29480883458974409
is 17 digits, so some calculation error should be expected. 所需的数字
29480883458974409
是17位数字,因此应该会出现一些计算错误。
In particular, sum += pow(base,i)*value[14-i]
is done as a long long = long long + (double * long long)
which results in long long = double
. 特别地,
sum += pow(base,i)*value[14-i]
是因为long long = long long + (double * long long)
导致long long = double
。 The nearest double
to 29480883458974409
is 29480883458974408
. 最近
double
到29480883458974409
是29480883458974408
。 So it is not an imprecise value from pow()
that causes the issue here, but an imprecise sum from the addition. 因此,造成此问题的不是
pow()
的不精确值,而是加法的不精确总和。
@Mooing Duck in a comment references code to avoid using pow()
and its double
limitation`. @Mooing Duck在注释中引用了代码,以避免使用
pow()
及其double
限制。 Following is a slight variant. 以下是一个轻微的变体。
unsigned long long ullongpow(unsigned value, unsigned exp) {
unsigned long long result = !!value;
while (exp-- > 0) {
result *= value;
}
return result;
}
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