c - Can anyone explain why my Merge Sort is not working? -

can please explain why not working? i'm having trouble getting numbers in array sorted , placed empty b array. i've searched high , low there seems eludes me, fellow cod3rz!

#include <stdio.h> #include <string.h>  void merge(int array[], int low, int mid, int high); void midpoint(int array[], int low, int high);  int main(int argc, const char * argv[]){      int b[100];      int array[] = { 13, 23, 37, 45, 55, 68, 79, 93};     int arraylength = sizeof(array)/sizeof(array[0]);       (int =0 ; < arraylength; i++){         ( int j= 1 + ; j < arraylength; j++){              midpoint(&array[i], ,j );{              }         printf("%d\n", *b);         }     }      return 0; }   void merge(int array[], int low, int mid, int high) {     int b[100];     int b[100];     int = low;     int b[100];     int j = mid + 1;     int b[100];     int k = 0;      while (i <= mid && j <= high) {         if (array[i] <= array[j])             b[k++] = array[i++];         else             b[k++] = array[j++];     }     while (i <= mid)         b[k++] = array[i++];      while (j <= high)         b[k++] = array[j++];      k--;     while (k > 0) {         array[low + k] = b[k];         k --;     }  }  void midpoint(int array[], int low, int high) {     int mid;     if (low < high) {         mid = (high + low)/2;         midpoint(array, low, mid);         midpoint(array, mid + 1, high);         merge(array, low, mid, high);     }  } 

first of all, you're not passing b array recursive calls, there no way it's going populated. furthermore, should able sorting in-place in array, of helper array assists merge operations. so, there no need b @ top level.

your merge() function bit reversed. should copy entire array array temp b array, , merge b array.

that way, when algorithm finished, array sorted @ top level, , have sorted array.

also, remove nested loops. since mergesort recursive divide , conquer algorithm, should start 1 call midpoint(), , recursion take care of rest if implemented correctly.

so this:

 (int =0 ; < arraylength; i++){         ( int j= 1 + ; j < arraylength; j++){              midpoint(&array[i], ,j );{          }         printf("%d\n", *b);     } 

should this:

 midpoint(array, 0 ,arraylength-1 ); 

also, have bracket issue, take out opening bracket line, , clean closing brackets necessary:

midpoint(&array[i], ,j );{

edit: there lot more problems in there aside outlined above. i'm hesitant spoon-feed answer since school assignment, since made effort , general code structure correct, , it's not can't search , find similar solutions online, i'll go ahead , post this.

here working solution implements mergesort algorithm based on code:

#include <stdio.h> #include <string.h>  void merge(int *array, int low, int mid, int high); void midpoint(int *array, int low, int high);  int main(int argc, const char * argv[]){      int array[] = { 100, 13, 44, 23, 22, 37, 3, 45, 2, 55, 68, 1, 79, 93, 4};     int arraylength = sizeof(array)/sizeof(array[0]);      //start recursive calls     midpoint(array, 0 ,arraylength-1 );      int i;     (i = 0; < arraylength; i++ ){         printf("%d\n", array[i]);     }      return 0; }   void merge(int *array, int low, int mid, int high) {     int b[100];      //copy current elements temp array     int v;     (v = low; v <= high; v++){         b[v] = array[v];     }      int = low;     int j = mid + 1;     int k = low;      //merge left side , right side array in sorted order     while (i <= mid && j <= high) {         if (b[i] <= b[j])             array[k++] = b[i++];         else             array[k++] = b[j++];     }      //the left side might have left-over elements     while (i <= mid)         array[k++] = b[i++];   }  void midpoint(int *array, int low, int high) {     int mid;     if (low < high) {         mid = (high + low)/2;         midpoint(array, low, mid);         midpoint(array, mid + 1, high);         merge(array, low, mid, high);     }  } 

output:

1 2 3 4 13 22 23 37 44 45 55 68 79 93 100