c# - String format numbers to millions, thousands with rounding -

i'm trying format price display, , want display number million (m) or thousands (k) suffix, ever display @ 3 values, rounded down.

i found this question close want, doesn't handle rounding (specifically, rounding down)

likewise, with question have no control on rounding.

sample input/expected output:

1 = 1 10 = 10 100 = 100 1000 = 1k 100000 = 100k 125000 = 125k 125900 = 125k 1000000 = 1m 1250000 = 1.25m 1258000 = 1.25m 10000000 = 10m 10500000 = 10.5m 100000000 = 100m 100100000 = 100m 

i ever want display 3 values.

i can't see how can use "," custom specifier , specify rounding.

my initial thinking suggests need use combination of above, math.floor , .tostring() formatting magic, i'm not sure start.

can me out?

thanks in advance.

this should help, combined 1 of formatting techniques in other questions you've linked to.

  internal long maxthreesignificantdigits(long x)   {      int = (int)math.log10(x);      = math.max(0, - 2);      = (int)math.pow(10, i);      return x / * i;   } 

edit:

ok, how this?

 console.writeline(so30180672.formatnumber(1));  console.writeline(so30180672.formatnumber(12));  console.writeline(so30180672.formatnumber(123));  console.writeline(so30180672.formatnumber(1234));  console.writeline(so30180672.formatnumber(12345));  console.writeline(so30180672.formatnumber(123456));  console.writeline(so30180672.formatnumber(1234567));  console.writeline(so30180672.formatnumber(12345678));  console.writeline(so30180672.formatnumber(123456789)); 

following partially copied here: https://stackoverflow.com/a/23384710/253938

   internal class so30180672    {       internal static string formatnumber(long num)       {          num = maxthreesignificantdigits(num);           if (num >= 100000000)             return (num / 1000000d).tostring("0.#m");          if (num >= 1000000)             return (num / 1000000d).tostring("0.##m");          if (num >= 100000)             return (num / 1000d).tostring("0k");          if (num >= 100000)             return (num / 1000d).tostring("0.#k");          if (num >= 1000)             return (num / 1000d).tostring("0.##k");          return num.tostring("#,0");       }         internal static long maxthreesignificantdigits(long x)       {          int = (int)math.log10(x);          = math.max(0, - 2);          = (int)math.pow(10, i);          return x / * i;       }    } 

edit 2 - thank @rhexis

   internal class so30180672    {       internal static void runtest()       {          console.writeline(formatnumber(1));          console.writeline(formatnumber(10));          console.writeline(formatnumber(100));          console.writeline(formatnumber(1000));          console.writeline(formatnumber(10000));          console.writeline(formatnumber(100000));          console.writeline(formatnumber(125000));          console.writeline(formatnumber(125900));          console.writeline(formatnumber(1000000));          console.writeline(formatnumber(1250000));          console.writeline(formatnumber(1258000));          console.writeline(formatnumber(10000000));          console.writeline(formatnumber(10500000));          console.writeline(formatnumber(100000000));          console.writeline(formatnumber(100100000));       }        private static string formatnumber(long num)       {          // ensure number has max 3 significant digits (no rounding can happen)          long = (long)math.pow(10, (int)math.max(0, math.log10(num) - 2));          num = num / * i;           if (num >= 1000000000)             return (num / 1000000000d).tostring("0.##") + "b";          if (num >= 1000000)             return (num / 1000000d).tostring("0.##") + "m";          if (num >= 1000)             return (num / 1000d).tostring("0.##") + "k";           return num.tostring("#,0");       }    }