如何获得 int (C#) 中的第一个数字？
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How can you get the first digit in an int (C#)?
提问by Dinah
In C#, what's the best way to get the 1st digit in an int? The method I came up with is to turn the int into a string, find the 1st char of the string, then turn it back to an int.
在 C# 中，获取 int 中第一个数字的最佳方法是什么？我想出的方法是将 int 转换为字符串，找到字符串的第一个字符，然后将其转换回 int。
int start = Convert.ToInt32(curr.ToString().Substring(0, 1));
While this does the job, it feels like there is probably a good, simple, math-based solution to such a problem. String manipulation feels clunky.
虽然这样做可以解决问题，但感觉可能有一个很好的、简单的、基于数学的解决方案来解决这样的问题。字符串操作感觉很笨重。
Edit:irrespective of speed differences, mystring[0] instead of Substring() is still just string manipulation
编辑：无论速度差异如何， mystring[0] 而不是 Substring() 仍然只是字符串操作
采纳答案by Anton Gogolev
Here's how
就是这样
int i = Math.Abs(386792);
while(i >= 10)
i /= 10;
and iwill contain what you need
并且i将包含你所需要的
回答by Keltex
Very simple (and probably quite fast because it only involves comparisons and one division):
非常简单（而且可能相当快，因为它只涉及比较和一个除法）：
if(i<10)
firstdigit = i;
else if (i<100)
firstdigit = i/10;
else if (i<1000)
firstdigit = i/100;
else if (i<10000)
firstdigit = i/1000;
else if (i<100000)
firstdigit = i/10000;
else (etc... all the way up to 1000000000)
回答by jgauffin
int myNumber = 8383;
char firstDigit = myNumber.ToString()[0];
// char = '8'
回答by JaredPar
Try this
尝试这个
public int GetFirstDigit(int number) {
if ( number < 10 ) {
return number;
}
return GetFirstDigit ( (number - (number % 10)) / 10);
}
EDIT
编辑
Several people have requested the loop version
有几个人要求循环版本
public static int GetFirstDigitLoop(int number)
{
while (number >= 10)
{
number = (number - (number % 10)) / 10;
}
return number;
}
回答by Lennaert
The best I can come up with is:
我能想到的最好的是：
int numberOfDigits = Convert.ToInt32(Math.Floor( Math.Log10( value ) ) );
int firstDigit = value / Math.Pow( 10, numberOfDigits );
...
...
Not very pretty :)
不是很漂亮:)
[Edited: first answer was really bad :) ]
[编辑：第一个答案真的很糟糕:)]
[Edit 2: I would probably advise the string manipulating solutions, though]
[编辑 2：不过，我可能会建议字符串操作解决方案]
[Edit 3: code formatting isnice :) ]
[编辑3：码格式是好:)]
回答by Douglas Leeder
int temp = i;
while (temp >= 10)
{
temp /= 10;
}
Result in temp
导致 temp
回答by JoshJordan
Just to give you an alternative, you could repeatedly divide the integer by 10, and then rollback one value once you reach zero. Since string operations are generally slow, this may be faster than string manipulation, but is by no means elegant.
只是给您一个替代方案，您可以重复将整数除以 10，然后在达到零时回滚一个值。由于字符串操作通常很慢，这可能比字符串操作快，但绝不优雅。
Something like this:
像这样的东西：
while(curr>=10)
curr /= 10;
回答by cjk
while (i > 10)
{
i = (Int32)Math.Floor((Decimal)i / 10);
}
// i is now the first int
回答by sdellysse
start = getFirstDigit(start);
public int getFirstDigit(final int start){
int number = Math.abs(start);
while(number > 10){
number /= 10;
}
return number;
}
or
或者
public int getFirstDigit(final int start){
return getFirstDigit(Math.abs(start), true);
}
private int getFirstDigit(final int start, final boolean recurse){
if(start < 10){
return start;
}
return getFirstDigit(start / 10, recurse);
}
回答by MartinStettner
int start = curr;
while (start >= 10)
start /= 10;
This is more efficient than a ToString() approach which internally must implement a similar loop and has to construct (and parse) a string object on the way ...
这比 ToString() 方法更有效，后者必须在内部实现类似的循环，并且必须在途中构造（并解析）一个字符串对象......
