c++ - Multiple definition, not in a header? Why does floor return a double? -

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i tried program merge sort function using static arrays , of course have incomprehensible error.

so first question when compile program gives me multiple definition error on line 9 of code:

#include <cmath> #include "include\sort.h"   /* theses fonctions accept arrays of unsigned short int length in unsigned int */  unsigned short int* sortbyfusion(unsigned short int arr[]) { // here !!!!!!!!     const unsigned int arrsize = sizeof(arr)/sizeof(unsigned short int);     if (arrsize <= 1) {return arr;}      /*     declarations , initializations of 2 half array     */     const unsigned int arrleftsize = static_cast<unsigned int>(floor(arrsize/2));     const unsigned int arrrightsize = static_cast<unsigned int>(arrsize - arrleftsize);      unsigned short int arrleft[arrleftsize];     unsigned short int arrright[arrrightsize];      (unsigned int = 0; < arrleftsize; ++)         arrleft[i] = arr[i];     (unsigned int = 0; < arrrightsize; ++)         arrright[i] = arr[i + arrleftsize];      /*     sort 2 arrays     */     (unsigned int = 0; < arrleftsize; ++)         arrleft[i] = *(sortbyfusion(arrleft) + i);     (unsigned int = 0; < arrrightsize; ++)         arrright[i] = *(sortbyfusion(arrright) + i);      /*     , fusion them     */     unsigned int i(0), j(0);     (unsigned int k = 0; k < arrsize; k ++) {         if (i >= arrleftsize)           {arr[k] = arrright[j]; j ++;} //that line         else if (j >= arrrightsize)     {arr[k] = arrleft[i]; ++;}  //and line here avoid segmentation fault         else {             if (arrleft[i] <= arrright[j]) {arr[k] = arrleft[i]; ++;}             else {arr[k] = arrright[j]; j ++;}         }     } return arr; }

what did wrong? tried put ifndef define endif did nothing more. seems has problem multiple definition bit different on forum.

secondly, used static_cast why floor return double when pass double argument? logically, should give integer (the floor of number integer ...)?

for compiler, gnu gcc, don't know how find version. , work code::blocks.

and header file :

#ifndef sort_h_included #define sort_h_included  unsigned short int* sortbyfusion(unsigned short int arr[]);  #endif // sort_h_included 

 const unsigned int arrsize = sizeof(arr)/sizeof(unsigned short int);

this line not working expected, because c++ doesn't keep information length of array runtime array - pointer array, sizeof(arr) returns sizeof(unsigned short int*) size of pointer.

as why there error in line 9, can't without seeing header sort.h.

//static_cast<unsigned int>(floor(arrsize/2)); // wrong arrsize/2; // right, c++ floor integer divisions. 
unsigned short int arrleft[arrleftsize]; unsigned short int arrright[arrrightsize];

these 2 lines aren't valid c++ because length of declared arrays can not determined @ compile time.


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