Develop Reference

(C#) How can I make all these "else if" statements more condensed and how can I optimize my code better?

Okay, I have a load of else if statements, is there a way to condense them into fewer lines of code? Like make one if statement for all of it? And what ways could I make my code more optimize and easier to read?
int x;
int y;
int time=0;
Random rng = new Random();
int hrand_num = rng.Next(-24000, 24000);
int vrand_num = rng.Next(-24000, 24000);
x = hrand_num;
y = vrand_num;
while (true)
{
ConsoleKey key = Console.ReadKey().Key;
if (key == ConsoleKey.UpArrow)
{
y=y+2000;
}
else if (key == ConsoleKey.DownArrow)
{
y=y-2000;
}
else if (key == ConsoleKey.LeftArrow)
{
x = x-1000;
}
else if (key == ConsoleKey.RightArrow)
{
x = x+1000;
}
// Circumnavigate Players Position.
// North and South
if (y >= 24001)
{
y = -24000;
}
else if (y <= -24001)
{
y = 24000;
}
//West and East
else if (x >= 24001)
{
x = -24000;
}
else if (x <= -24001)
{
x = 24000;
}
// Setting Time Zones
if (x >= -2000 && x <= 0 )
{
time = 0;
}
else if (x >=
1 && x <= 2000)
{
time = 1;
}
else if (x >= 2001 && x <=4000)
{
time = 2;
}
else if (x >= 4001 && x <= 6000)
{
time = 3;
}
else if (x >= 6001 && x <= 8000)
{
time = 4;
}
else if (x >= 8001 && x <= 10000)
{
time = 5;
}
else if (x >= 10001 && x <= 12000)
{
time = 6;
}
else if (x >= 12001 && x <= 14000)
{
time = 7;
}
else if (x >= 14001 && x <= 16000)
{
time = 8;
}
else if (x >= 16001 && x <= 18000)
{
time = 9;
}
else if (x >= 18001 && x <= 20000)
{
time = 10;
}
else if (x >= 20001 && x <= 22000)
{
time = 11;
}
else if (x >= 22001 && x <= 24000)
{
time = 12;
}
else if (x == -24000 && x <= -22001)
{
time = 13;
}
else if (x >= -22000 && x <= -20001 )
{
time = 14;
}
else if (x >= -20000 && x <= -18001)
{
time = 15;
}
else if (x >= -18000 && x <= -16001)
{
time = 16;
}
else if (x >= -16000 && x <= -14001)
{
time = 17;
}
else if (x >= -14000 && x <= -12001)
{
time = 18;
}
else if (x >= -12000 && x <= -10001)
{
time = 19;
}
else if (x >= -10000 && x <= -8001)
{
time = 20;
}
else if (x >= -8000 && x <= -6001)
{
time = 21;
}
else if (x >= -6000 && x <= -4001)
{
time = 22;
}
else if (x >= -4000 && x <= -2001)
{
time = 23;
}
Console.WriteLine($"X: {x,6} Y: {y,6} Time: {time,3}");
}
```

Assuming that you are using C# 8.0 you may have a look at the switch statement and switch expressions: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/switch-expression (additionaly the patterns documentation is also helpful: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/patterns)
So you could write something like:
switch (key)
{
case ConsoleKey.UpArrow:
y=y+2000;
break;
// [...]
}
time = x switch
{
>= -2000 and <= 0 => 0,
>= 1 and <= 2000 => 1
// [...]
};

I would suggest that you take advantage of:
a switch statement for interpreting the arrow key
comparing the switch statement to an if loop, you can think of the first case as being the if condition and the remaning cases as being the else if conditions
Math.Abs( ) and Math.Sign( ) for circumnavigating the player's position
Math.Abs( ) returns the absolute value of the variable; e.g. will Math.Abs(x) return 5 both for x = 5 and x = -5
Math.Sign( ) returns the sign of the value; if the value is a negative number, it returns -1; if it's a positive number, it returns 1; if it's neither (0), it returns 0. This helps us determine the wanted sign of the updated value.
a switch expression for setting the time
seeing as the time value alone is determined by x in the end, you can use a switch expression rather than a switch statement to determine its value. The switch expression says that you want to determine the value of time based on the value of x; and each following condition is compared to x (<= -22001 is computed as x <= -22001). If the condition evaluates to true, the provided value is set as the value of time (=> 13 then sets time = 13).
It could be implemented like this:
int x;
int y;
Random rng = new Random();
int hrand_num = rng.Next(-24000, 24000);
int vrand_num = rng.Next(-24000, 24000);
x = hrand_num;
y = vrand_num;
while (true)
{
switch (Console.ReadKey().Key)
{
case ConsoleKey.UpArrow:
y += 2000;
break;
case ConsoleKey.DownArrow:
y -= 2000;
break;
case ConsoleKey.LeftArrow:
x -= 1000;
break;
case ConsoleKey.RightArrow:
x += 1000;
break;
}
// Circumnavigate Players Position.
// North and South
if (Math.Abs(y) > 24000)
{
y = -(Math.Sign(y) * 24000);
}
//West and East
else if (Math.Abs(x) > 24000)
{
x = -(Math.Sign(x) * 24000);
}
// Setting Time Zones
var time = x switch
{
<= -22001 => 13,
<= -20001 => 14,
<= -18001 => 15,
<= -16001 => 16,
<= -14001 => 17,
<= -12001 => 18,
<= -10001 => 19,
<= -8001 => 20,
<= -6001 => 21,
<= -4001 => 22,
<= -2001 => 23,
<= 0 => 0,
<= 2000 => 1,
<= 4000 => 2,
<= 6000 => 3,
<= 8000 => 4,
<= 10000 => 5,
<= 12000 => 6,
<= 14000 => 7,
<= 16000 => 8,
<= 18000 => 9,
<= 20000 => 10,
<= 22000 => 11,
<= 24000 => 12,
_ => 0
};
Console.WriteLine($"X: {x,6} Y: {y,6} Time: {time,3}");
I would also suggest introducing some constants; particularily for the value 24000.

You can use the following to cover all time cases
var time = x <= 24000
? x / 2000 + 1;
: (24000 - x) / 2000 + 13;

find common substrings in 2 string in c#

I have strings like:
1) Cookie:ystat_tw_ss376223=9_16940400_234398;
2) Cookie:zynga_toolbar_fb_uid=1018132522
3) GET /2009/visuels/Metaboli_120x600_UK.gif HTTP/1.1
4) GET /2010/07/15/ipad-3hk-smv-price-hk/ HTTP/1.1
1 ad 2 have common substtring{cookie:}
3 and 4 have common substtring{GET /20, HTTP/1.1}
I want to find all common substrings that have the length more than three characters(contain space character) between 2 strings.(like 1 and 2)
i want to code in c#. i have a program but it has some problems.
Could anyone help me?
public static string[] MyMCS2(string a, string b)
{
string[] st = new string[100];
// List<string> st = new List<string>();
List<char> f = new List<char>();
int ctr = 0;
char[] str1 = a.ToCharArray();
char[] str2 = b.ToCharArray();
int m = 0;
int n = 0;
while (m < str1.Length)
{
for (n = 0; n < str2.Length; n++)
{
if (m < str1.Length)
{
if (str1[m] == str2[n])
{
if ((m > 1) && (n > 1) &&(str1[m - 1] == str2[n - 1]) && (str1[m - 2] == str2[n - 2]))
{
//f[m]= str1[m];
f.Add(str1[m]);
char[] ff = f.ToArray();
string aaa = new string(ff);
if (aaa.Length >= 3)
{
st[ctr] = aaa + "()";
//st.Add(aaa);
ctr++;
}
kk = m;
m++;
}
else if ((n == 0) ||(n == 1))
{
f.Add(str1[m]);
kk = m;
m++;
}
else
f.Clear();
}
//else if ((str1[m] == str2[n]) && (m == str1.Length - 1) && (n == str2.Length - 1))
//{
// f.Add(str1[m]);
// char[] ff = f.ToArray();
// string aaa = new string(ff);
// if (aaa.Length >= 3)
// {
// st[ctr] = aaa;
// ctr++;
// }
// // m++;
//}
else if ((str1[m] != str2[n]) && (n == (str2.Length - 1)))
{
m++;
}
else if ((m > 1) && (n > 1) && (str1[m] != str2[n]) && (str1[m - 1] == str2[n - 1]) && (str1[m - 2] == str2[n - 2]) && (str1[m - 3] == str2[n - 3]))
{
//
char[] ff = f.ToArray();
string aaa = new string(ff);
if (aaa.Length >= 3)
{
st[ctr] = aaa + "()" ;
//st.Add(aaa);
ctr++;
f.Clear();
}
//f.Clear();
//for (int h = 0; h < ff.Length; h++)
//{
// f[h] = '\0';
//}
}
else if (str1[m] != str2[n])
continue;
}
}
}
//int gb = st.Length;
return st;
}

This is an exact matching problem not a substring. You can solve it with aho-corasick algorithm. Use the first string and compute a finite state machine. Then process the search string. You can extend the aho-corasick algorithm to use a wildcard and search also for substrings. You can try this animated example: http://blog.ivank.net/aho-corasick-algorithm-in-as3.html

C# Check for neighbours

I have a function to check neighbors of an array and if that element is equal with 1. X is for each neighbor found and v[l] is the position for each 0. I have a problem with this code each time gives me "Index was outside the bounds of the array" and i don't know what to do else.
public int modificari(int i,int j,int n,int m)
{
int x = 0;
v = new int[n];
l=0;
if (mat[i, j] == 1)
{
if (j++ < m)
{
if (mat[i, j++] == 1)
x++;
else
{
v[l] = i * n + j + 2;
l++;
}
}
if (j++ < m && i++ < n)
{
if (mat[i++, j++] == 1)
x++;
else
{
v[l] = (i + 1) * n + j + 2;
l++;
}
}
if (i++ < n)
{
if (mat[i++, j] == 1)
x++;
else
{
v[l] = (i + 1) * n + j + 1;
l++;
}
}
if (j-- >= 0 && i++ < n)
{
if (mat[i++, j--] == 1)
x++;
else
{
v[l] = (i + 1) * n + j;
l++;
}
}
if (j-- >= 0)
{
if (mat[i, j--] == 1)
x++;
else
{
v[l] = i * n + j;
l++;
}
}
if (j-- >= 0 && i-- >= 0)
{
if (mat[i--, j--] == 1)
x++;
else
{
v[l] = (i - 1) * n + j;
l++;
}
}
if (i-- >= 0)
{
if (mat[i--, j] == 1)
x++;
else
{
v[l] = (i - 1) * n + j + 1;
l++;
}
}
if (j < n && i-- >= 0)
{
if (mat[i--, j++] == 1)
x++;
else
{
v[l] = (i - 1) * n + j + 2;
l++;
}
}
if (x < 2 && x > 3)
return 1;
else
return random();
}
return x;
}

That is a total mess. It is very hard to follow, even for an experienced coder. Use of one letter variable names and inline ++ operators is usually discouraged for the sake of readability.
I've quickly tried to rewrite your function from my best guess of what you're trying to achieve. I'm hoping you can see a different way to approach the problem that suits you better.
NOTE: I did not test this code at all, it probably has compile errors.
public struct Point
{
public int X;
public int Y;
public Point( int x, int y )
{
X = x;
Y = y;
}
}
public class Whatever
{
// ...
// Here is a list of the positions of all the neighbours whose values are
// zero.
List<Point> zeroPositions = new List<Point>();
// ...
public int Modificari(int pointX, int pointY)
{
// Determine dimensions of array.
int height = mat.GetLength(0);
int width = mat.GetLength(1);
// Find the minimum and maximum positions bounded by array size. (So we
// don't try to look at cell (-1, -1) when considering the neighbours of
// cell (0, 0) for instance.
int left = Math.Max( pointX - 1, 0 );
int right = Math.Min( pointX + 1, width );
int top = Math.Max( pointY - 1, 0 );
int bottom = Math.Min( pointY + 1, height );
// This is the number of neighbours whose value is 1.
int oneCount = 0;
zeroPositions.Clear();
for( int y = top; y <= bottom; y++ )
{
for( int x = left; x <= right; x++ )
{
if( mat[x, y] == 1 )
{
oneCount++;
}
else if( mat[x, y] == 0 )
{
zeroPositions.Add( new Point( x, y ) );
}
}
}
return oneCount;
}
//...
}
Also I'd really advise you to try not to do too many things in a function. Try making a different function for getting positions of ones and for returning the number of zeros.

dragging issue in chess table

I have chess table and my elements are now moving according to rules .But when I drag out of rules my button is disappearing...How I can solve it ???
(red buttons are showing where can I go my elements)
for example knight is moving as rules now (if I don't pass over the red buttons there is no problem)but when I pass over the red places and if I drop there the knight disappears and red places turns back to their original color ( no more red places which indicates where my knight can go ). i tried to make debug but since i am new in c# and debugging i haven't solved the problem. i will be happy if u enlighten my way. how can i solve it? thanks
void btn_DragEnter(object sender, DragEventArgs e)
{
Button button = (Button)sender;
e.Effect = DragDropEffects.Move;
for (int x = 0; x <= 7; x++)
{
for (int y = 0; y <= 7; y++)
{
btn[x, y].Image = null;
if ((x + y) % 2 == 0)
btn[x, y].BackColor = Color.Black;
else
btn[x, y].BackColor = Color.White;
}
}
}
void btn_DragDrop(object sender, DragEventArgs e)
{
Button button = (Button)sender;
button.Image = (Bitmap)e.Data.GetData(DataFormats.Bitmap);
int[] dizi = (int[])button.Tag;
int x = dizi[0];
int y = dizi[1];
for (int a = 0; a <= 7; a++)
{
for (int b = 0; b <= 7; b++)
{
btn[a, b].AllowDrop = false;
}
}
if ((x + 1 >= 0 && y + 2 <= 7) && (y + 2 >= 0 && x + 1 <= 7))
{
btn[x + 1, y + 2].BackColor = Color.Red;
btn[x + 1, y + 2].AllowDrop = true;
}
if ((x + 1 >= 0 && y - 2 <= 7) && (y - 2 >= 0 && x + 1 <= 7))
{
btn[x + 1, y - 2].BackColor = Color.Red;
btn[x + 1, y - 2].AllowDrop = true;
}
if ((x - 1 >= 0 && y + 2 <= 7) && (y + 2 >= 0 && x - 1 <= 7))
{
btn[x - 1, y + 2].BackColor = Color.Red;
btn[x - 1, y + 2].AllowDrop = true;
}
if ((x - 1 >= 0 && y - 2 <= 7) && (y - 2 >= 0 && x - 1 <= 7))
{
btn[x - 1, y - 2].BackColor = Color.Red;
btn[x - 1, y - 2].AllowDrop = true;
}
if ((x + 2 >= 0 && y + 1 <= 7) && (y + 1 >= 0 && x + 2 <= 7))
{
btn[x + 2, y + 1].BackColor = Color.Red;
btn[x + 2, y + 1].AllowDrop = true;
}
if ((x + 2 >= 0 && y - 1 <= 7) && (y - 1 >= 0 && x + 2 <= 7))
{
btn[x + 2, y - 1].BackColor = Color.Red;
btn[x + 2, y - 1].AllowDrop = true;
}
if ((x - 2 >= 0 && y + 1 <= 7) && (y + 1 >= 0 && x - 2 <= 7))
{
btn[x - 2, y + 1].BackColor = Color.Red;
btn[x - 2, y + 1].AllowDrop = true;
}
if ((x - 2 >= 0 && y - 1 <= 7) && (y - 1 >= 0 && x - 2 <= 7))
{
btn[x - 2, y - 1].BackColor = Color.Red;
btn[x - 2, y - 1].AllowDrop = true;
}
}

DoDragDrop is called only when actually dropping the piece. Your logic for determining where the piece can be dropped should be run when starting the drag, in MouseDown or MouseMove, before the call to DoDragDrop. It also seems you are clearing the red buttons in the DragEnter function. That also should be done in the MouseDown/MouseMove function, after the call to DoDragDrop.

Faster parsing of numbers on .NET

I have written two functions that convert a string of whitespace-separated integers into an int array. The first function uses Substring and then applies System.Int32.Parse to convert the substring into an int value:
let intsOfString (s: string) =
let ints = ResizeArray()
let rec inside i j =
if j = s.Length then
ints.Add(s.Substring(i, j-i) |> System.Int32.Parse)
else
let c = s.[j]
if '0' <= c && c <= '9' then
inside i (j+1)
else
ints.Add(s.Substring(i, j-i) |> System.Int32.Parse)
outside (j+1)
and outside i =
if i < s.Length then
let c = s.[i]
if '0' <= c && c <= '9' then
inside i (i+1)
else
outside (i+1)
outside 0
ints.ToArray()
The second function traverses the characters of the string in-place accumulating the integer without creating a temporary substring:
let intsOfString (s: string) =
let ints = ResizeArray()
let rec inside n i =
if i = s.Length then
ints.Add n
else
let c = s.[i]
if '0' <= c && c <= '9' then
inside (10*n + int c - 48) (i+1)
else
ints.Add n
outside(i+1)
and outside i =
if i < s.Length then
let c = s.[i]
if '0' <= c && c <= '9' then
inside (int c - 48) (i+1)
else
outside (i+1)
outside 0
ints.ToArray()
Benchmarking on space-separated integers 1 to 1,000,000, the first version takes 1.5s whereas the second version takes 0.3s.
Parsing such values can be performance critical so leaving 5x performance on the table by using temporary substrings can be undesirable. Parsing integers is easy but parsing other values such as floating point numbers, decimals and dates is considerably harder.
So, are there built-in functions to parse directly from a substring within a string (i.e. using the given start and length of a string) in order to avoid generating a temporary string? If not, are there any libraries that provide efficient functions to do this?

System.Int32.Parse is slowlest, because it used CultureInfo, FormatInfo and etc; and performance reason is not in the temporary strings.
Code from reflection:
private unsafe static bool ParseNumber(ref char* str, NumberStyles options, ref Number.NumberBuffer number, NumberFormatInfo numfmt, bool parseDecimal)
{
number.scale = 0;
number.sign = false;
string text = null;
string text2 = null;
string str2 = null;
string str3 = null;
bool flag = false;
string str4;
string str5;
if ((options & NumberStyles.AllowCurrencySymbol) != NumberStyles.None)
{
text = numfmt.CurrencySymbol;
if (numfmt.ansiCurrencySymbol != null)
{
text2 = numfmt.ansiCurrencySymbol;
}
str2 = numfmt.NumberDecimalSeparator;
str3 = numfmt.NumberGroupSeparator;
str4 = numfmt.CurrencyDecimalSeparator;
str5 = numfmt.CurrencyGroupSeparator;
flag = true;
}
else
{
str4 = numfmt.NumberDecimalSeparator;
str5 = numfmt.NumberGroupSeparator;
}
int num = 0;
char* ptr = str;
char c = *ptr;
while (true)
{
if (!Number.IsWhite(c) || (options & NumberStyles.AllowLeadingWhite) == NumberStyles.None || ((num & 1) != 0 && ((num & 1) == 0 || ((num & 32) == 0 && numfmt.numberNegativePattern != 2))))
{
bool flag2;
char* ptr2;
if ((flag2 = (((options & NumberStyles.AllowLeadingSign) == NumberStyles.None) ? false : ((num & 1) == 0))) && (ptr2 = Number.MatchChars(ptr, numfmt.positiveSign)) != null)
{
num |= 1;
ptr = ptr2 - (IntPtr)2 / 2;
}
else
{
if (flag2 && (ptr2 = Number.MatchChars(ptr, numfmt.negativeSign)) != null)
{
num |= 1;
number.sign = true;
ptr = ptr2 - (IntPtr)2 / 2;
}
else
{
if (c == '(' && (options & NumberStyles.AllowParentheses) != NumberStyles.None && (num & 1) == 0)
{
num |= 3;
number.sign = true;
}
else
{
if ((text == null || (ptr2 = Number.MatchChars(ptr, text)) == null) && (text2 == null || (ptr2 = Number.MatchChars(ptr, text2)) == null))
{
break;
}
num |= 32;
text = null;
text2 = null;
ptr = ptr2 - (IntPtr)2 / 2;
}
}
}
}
c = *(ptr += (IntPtr)2 / 2);
}
int num2 = 0;
int num3 = 0;
while (true)
{
if ((c >= '0' && c <= '9') || ((options & NumberStyles.AllowHexSpecifier) != NumberStyles.None && ((c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F'))))
{
num |= 4;
if (c != '0' || (num & 8) != 0)
{
if (num2 < 50)
{
number.digits[(IntPtr)(num2++)] = c;
if (c != '0' || parseDecimal)
{
num3 = num2;
}
}
if ((num & 16) == 0)
{
number.scale++;
}
num |= 8;
}
else
{
if ((num & 16) != 0)
{
number.scale--;
}
}
}
else
{
char* ptr2;
if ((options & NumberStyles.AllowDecimalPoint) != NumberStyles.None && (num & 16) == 0 && ((ptr2 = Number.MatchChars(ptr, str4)) != null || (flag && (num & 32) == 0 && (ptr2 = Number.MatchChars(ptr, str2)) != null)))
{
num |= 16;
ptr = ptr2 - (IntPtr)2 / 2;
}
else
{
if ((options & NumberStyles.AllowThousands) == NumberStyles.None || (num & 4) == 0 || (num & 16) != 0 || ((ptr2 = Number.MatchChars(ptr, str5)) == null && (!flag || (num & 32) != 0 || (ptr2 = Number.MatchChars(ptr, str3)) == null)))
{
break;
}
ptr = ptr2 - (IntPtr)2 / 2;
}
}
c = *(ptr += (IntPtr)2 / 2);
}
bool flag3 = false;
number.precision = num3;
number.digits[(IntPtr)num3] = '\0';
if ((num & 4) != 0)
{
if ((c == 'E' || c == 'e') && (options & NumberStyles.AllowExponent) != NumberStyles.None)
{
char* ptr3 = ptr;
c = *(ptr += (IntPtr)2 / 2);
char* ptr2;
if ((ptr2 = Number.MatchChars(ptr, numfmt.positiveSign)) != null)
{
c = *(ptr = ptr2);
}
else
{
if ((ptr2 = Number.MatchChars(ptr, numfmt.negativeSign)) != null)
{
c = *(ptr = ptr2);
flag3 = true;
}
}
if (c >= '0' && c <= '9')
{
int num4 = 0;
do
{
num4 = num4 * 10 + (int)(c - '0');
c = *(ptr += (IntPtr)2 / 2);
if (num4 > 1000)
{
num4 = 9999;
while (c >= '0' && c <= '9')
{
c = *(ptr += (IntPtr)2 / 2);
}
}
}
while (c >= '0' && c <= '9');
if (flag3)
{
num4 = -num4;
}
number.scale += num4;
}
else
{
ptr = ptr3;
c = *ptr;
}
}
while (true)
{
if (!Number.IsWhite(c) || (options & NumberStyles.AllowTrailingWhite) == NumberStyles.None)
{
bool flag2;
char* ptr2;
if ((flag2 = (((options & NumberStyles.AllowTrailingSign) == NumberStyles.None) ? false : ((num & 1) == 0))) && (ptr2 = Number.MatchChars(ptr, numfmt.positiveSign)) != null)
{
num |= 1;
ptr = ptr2 - (IntPtr)2 / 2;
}
else
{
if (flag2 && (ptr2 = Number.MatchChars(ptr, numfmt.negativeSign)) != null)
{
num |= 1;
number.sign = true;
ptr = ptr2 - (IntPtr)2 / 2;
}
else
{
if (c == ')' && (num & 2) != 0)
{
num &= -3;
}
else
{
if ((text == null || (ptr2 = Number.MatchChars(ptr, text)) == null) && (text2 == null || (ptr2 = Number.MatchChars(ptr, text2)) == null))
{
break;
}
text = null;
text2 = null;
ptr = ptr2 - (IntPtr)2 / 2;
}
}
}
}
c = *(ptr += (IntPtr)2 / 2);
}
if ((num & 2) == 0)
{
if ((num & 8) == 0)
{
if (!parseDecimal)
{
number.scale = 0;
}
if ((num & 16) == 0)
{
number.sign = false;
}
}
str = ptr;
return true;
}
}
str = ptr;
return false;
}
public static int Parse(string s)
{
return Number.ParseInt32(s, NumberStyles.Integer, NumberFormatInfo.CurrentInfo);
}
internal unsafe static int ParseInt32(string s, NumberStyles style, NumberFormatInfo info)
{
byte* stackBuffer = stackalloc byte[1 * 114 / 1];
Number.NumberBuffer numberBuffer = new Number.NumberBuffer(stackBuffer);
int result = 0;
Number.StringToNumber(s, style, ref numberBuffer, info, false);
if ((style & NumberStyles.AllowHexSpecifier) != NumberStyles.None)
{
if (!Number.HexNumberToInt32(ref numberBuffer, ref result))
{
throw new OverflowException(Environment.GetResourceString("Overflow_Int32"));
}
}
else
{
if (!Number.NumberToInt32(ref numberBuffer, ref result))
{
throw new OverflowException(Environment.GetResourceString("Overflow_Int32"));
}
}
return result;
}
private unsafe static void StringToNumber(string str, NumberStyles options, ref Number.NumberBuffer number, NumberFormatInfo info, bool parseDecimal)
{
if (str == null)
{
throw new ArgumentNullException("String");
}
fixed (char* ptr = str)
{
char* ptr2 = ptr;
if (!Number.ParseNumber(ref ptr2, options, ref number, info, parseDecimal) || ((ptr2 - ptr / 2) / 2 < str.Length && !Number.TrailingZeros(str, (ptr2 - ptr / 2) / 2)))
{
throw new FormatException(Environment.GetResourceString("Format_InvalidString"));
}
}
}

I've written this one for doubles, that doesn't create a temporary substring. It's meant to be used inside a JSON parser so it limits itself to how doubles can be represented in JSON according to http://www.json.org/.
It's not optimal yet because it requires you to know where the number begins and ends (begin and end parameters), so you'll have to traverse the length of the number twice to find out where it ends. It's still around 10-15x faster than double.Parse and it could be fairly easily modified that it finds the end inside the function which is then returned as an out parameter to know where you have to resume parsing the main string.
Used like so:
Parsers.TryParseDoubleFastStream("1", 0, 1, out j);
Parsers.TryParseDoubleFastStream("2.0", 0, 3, out j);
Parsers.TryParseDoubleFastStream("3.5", 0, 3, out j);
Parsers.TryParseDoubleFastStream("-4.5", 0, 4, out j);
Parsers.TryParseDoubleFastStream("50.06", 0, 5, out j);
Parsers.TryParseDoubleFastStream("1000.65", 0, 7, out j);
Parsers.TryParseDoubleFastStream("-10000.8600", 0, 11, out j);
Code can be found here:
https://gist.github.com/3010984 (would be too lengthy to post here).
And StandardFunctions.IgnoreChar is for my purpose as simple as:
public static bool IgnoreChar(char c)
{
return c < 33;
}

Paste all this code into C# and call Test(). This is as close as you can get to operating directly on the string array to parse numbers using C#. It is built for speed, not elegance. The ParseInt and ParseFloat function were created for an OpenGL graphics engine to import vectors from text-based 3d models. Parsing floats is a significant bottleneck in that process. This was as fast as I could make it.
using System.Diagnostics;
private void Test()
{
Stopwatch sw = new Stopwatch();
StringBuilder sb = new StringBuilder();
int iterations = 1000;
// Build a string of 1000000 space separated numbers
for (var n = 0; n < iterations; n++)
{
if (n > 0)
sb.Append(' ');
sb.Append(n.ToString());
}
string numberString = sb.ToString();
// Time the process
sw.Start();
StringToInts(numberString, iterations);
//StringToFloats(numberString, iterations);
sw.Stop();
long proc1 = sw.ElapsedMilliseconds;
Console.WriteLine("iterations: {0} \t {1}ms", iterations, proc1);
}
private unsafe int[] StringToInts(string s, int length)
{
int[] ints = new int[length];
int index = 0;
int startpos = 0;
fixed (char* pStringBuffer = s)
{
fixed (int* pIntBuffer = ints)
{
for (int n = 0; n < s.Length; n++)
{
if (s[n] == ' ' || n == s.Length - 1)
{
if (n == s.Length - 1)
n++;
// pIntBuffer[index++] = int.Parse(new string(pStringBuffer, startpos, n - startpos));
pIntBuffer[index++] = ParseInt((pStringBuffer + startpos), n - startpos);
startpos = n + 1;
}
}
}
}
return ints;
}
private unsafe float[] StringToFloats(string s, int length)
{
float[] floats = new float[length];
int index = 0;
int startpos = 0;
fixed (char* pStringBuffer = s)
{
fixed (float* pFloatBuffer = floats)
{
for (int n = 0; n < s.Length; n++)
{
if (s[n] == ' ' || n == s.Length - 1)
{
if (n == s.Length - 1)
n++;
pFloatBuffer[index++] = ParseFloat((pStringBuffer + startpos), n - startpos); // int.Parse(new string(pStringBuffer, startpos, n - startpos));
startpos = n + 1;
}
}
}
}
return floats;
}
public static unsafe int ParseInt(char* input, int len)
{
int pos = 0; // read pointer position
int part = 0; // the current part (int, float and sci parts of the number)
bool neg = false; // true if part is a negative number
int* ret = stackalloc int[1];
while (pos < len && (*(input + pos) > '9' || *(input + pos) < '0') && *(input + pos) != '-')
pos++;
// sign
if (*(input + pos) == '-')
{
neg = true;
pos++;
}
// integer part
while (pos < len && !(input[pos] > '9' || input[pos] < '0'))
part = part * 10 + (input[pos++] - '0');
*ret = neg ? (part * -1) : part;
return *ret;
}
public static unsafe float ParseFloat(char* input, int len)
{
//float ret = 0f; // return value
int pos = 0; // read pointer position
int part = 0; // the current part (int, float and sci parts of the number)
bool neg = false; // true if part is a negative number
float* ret = stackalloc float[1];
// find start
while (pos < len && (input[pos] < '0' || input[pos] > '9') && input[pos] != '-' && input[pos] != '.')
pos++;
// sign
if (input[pos] == '-')
{
neg = true;
pos++;
}
// integer part
while (pos < len && !(input[pos] > '9' || input[pos] < '0'))
part = part * 10 + (input[pos++] - '0');
*ret = neg ? (float)(part * -1) : (float)part;
// float part
if (pos < len && input[pos] == '.')
{
pos++;
double mul = 1;
part = 0;
while (pos < len && !(input[pos] > '9' || input[pos] < '0'))
{
part = part * 10 + (input[pos] - '0');
mul *= 10;
pos++;
}
if (neg)
*ret -= (float)part / (float)mul;
else
*ret += (float)part / (float)mul;
}
// scientific part
if (pos < len && (input[pos] == 'e' || input[pos] == 'E'))
{
pos++;
neg = (input[pos] == '-'); pos++;
part = 0;
while (pos < len && !(input[pos] > '9' || input[pos] < '0'))
{
part = part * 10 + (input[pos++] - '0');
}
if (neg)
*ret /= (float)Math.Pow(10d, (double)part);
else
*ret *= (float)Math.Pow(10d, (double)part);
}
return (float)*ret;
}

So, are there built-in functions to parse directly from a substring within a string (i.e.
using the given start and length of a string) in order to avoid generating a temporary
string? If not, are there any libraries that provide efficient functions to do this?
It seems that you want to use a lexing buffer and a lexer, similar to what OCaml can provide with ocamllex and the Lexbuf buffer. (I cannot provide references for F#.)
If your benchmark involving a huge string of integers separated by other tokens is your typical case, it will work well. But in other situations, it could be impractical.

Not sure if this is any good, but have you tried something like:
var stringValues = input.split(" ");
var intValues = Array.ConvertAll(stringValues, s => int.Parse(s));