Concatenate integers in C#

Question

Is there an inexpensive way to concatenate integers in csharp?

Example: 1039 & 7056 = 10397056

Answer 1

If you can find a situation where this is expensive enough to cause any concern, I'll be very impressed:

int a = 1039; int b = 7056;  int newNumber = int.Parse(a.ToString() + b.ToString()) 

Or, if you want it to be a little more ".NET-ish":

int newNumber = Convert.ToInt32(string.Format("{0}{1}", a, b)); 

int.Parse is not an expensive operation. Spend your time worrying about network I/O and O^N regexes.

Other notes: the overhead of instantiating StringBuilder means there's no point if you're only doing a few concatenations. And very importantly - if you are planning to turn this back into an integer, keep in mind it's limited to ~2,000,000,000. Concatenating numbers gets very large very quickly, and possibly well beyond the capacity of a 32-bit int. (signed of course).

Answer 2

I'm a bit late at the party, but recently I had to concatenate integers. With 0 < a,b < 10^9 it can be done quite fast.

static ulong concat(uint a, uint b) {     if (b < 10U) return 10UL * a + b;     if (b < 100U) return 100UL * a + b;     if (b < 1000U) return 1000UL * a + b;     if (b < 10000U) return 10000UL * a + b;     if (b < 100000U) return 100000UL * a + b;     if (b < 1000000U) return 1000000UL * a + b;     if (b < 10000000U) return 10000000UL * a + b;     if (b < 100000000U) return 100000000UL * a + b;     return 1000000000UL * a + b; } 

Edit: the version below might be interesting (platform target: x64).

static ulong concat(ulong a, uint b) {     const uint c0 = 10, c1 = 100, c2 = 1000, c3 = 10000, c4 = 100000,         c5 = 1000000, c6 = 10000000, c7 = 100000000, c8 = 1000000000;     a *= b < c0 ? c0 : b < c1 ? c1 : b < c2 ? c2 : b < c3 ? c3 :          b < c4 ? c4 : b < c5 ? c5 : b < c6 ? c6 : b < c7 ? c7 : c8;     return a + b; }