what is the maximum combination for generate random string of given length?

[Le rner]

Hi all, char possibles[37] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; i am renerating random string with help of rand function. how can i calculate the maximum combination for generate random string of given length? like if i give length = 4? so how cany maximum string generated of length 4 from given cahr array? please help me for this. thanks in advance.

[Rajesh R Subramanian]

It's known as Permutation[^], and there's formulae on that page that answers your question. By the way, this is not even a programming question, and has nothing to do with C++ or MFC.

"Real men drive manual transmission" - Rajesh.

[T RATHA KRISHNAN]

If order is important you have to use "Permutation". Otherwise you have to use "Combination". You have to select 4 characters out of the 36 characters. 36c4 is what you need. 36!/32!*4! is the way to calculate if my memory is good.

[enhzflep]

Depends on whether or not a character may be repeated in a string. If so, it's very,very,very easy: # combinations = pow(numCharsToChooseFrom, lengthOfGeneratedString) 4 char string - 37^4 = 1,874,161 5 char string - 37^5 = 69,343,957 If a character may not be repeated, it is a little more involved. # combinations = (numCharsToChooseFrom!) / ((numCharsToChooseFrom-lengthOfGeneratedString)!) 4 character string - 37 * 36 * 35 * 34 = 1,585,080 5 char string - 37 * 36 * 35 * 34 * 33 = 52,307,640 or to put it more simply 4 character string - (37! / 33!) = 1,585,080 5 char string - (37! / 32!) = 52,307,640 Where the ! operator means factorial[^].