c - something wrong with my dynamic array -

while add more 13 element, result seems not correct! code below! when add 12 elements, result

the no.0 0
no.1 1
no.2 2
no.3 3
no.4 4
no.5 5
no.6 6
no.7 7
no.8 8
no.9 9
no.10 10
no.11 11

when add 1 more, result changed lot, have no idea what's going on here:

the no.0 0
no.1 1
no.2 2
no.3 3
no.4 4
no.5 5
no.6 6
no.7 7
no.8 0
no.9 1
no.10 2
no.11 3
no.12 12

#include<stdio.h> #include<stdlib.h>  typedef struct dynarray myarray; struct dynarray {     int size;     int length;     int *array; };  myarray *create(void) {     /* todo: define arrays */     myarray *da;     da = malloc(sizeof(myarray));     da->size = 0;     da->length = 3;     da->array = (int *)malloc(da->length * sizeof(int));     return da; }   void add(myarray *array, int val) {     int i;     int length = array->length;     int size = array->size;     int *temp;     //printf("da->size1 = %d\nda->length1 = %d\n",array->size,array->length);      if (size == length) {         temp = (int *)malloc(length * sizeof(int));         (i = 0; i<size; i++) {             temp[i] = array->array[i];             printf("%d,", array->array[i]);         }           //printf("!@#$@#$=%d\n",array->length);          array->array = (int*)realloc(array->array, sizeof(int)*length);         (i = 0; i<size; i++)             array->array[i] = temp[i];         array->length *= 2;         length *= 2;     }     if (size <length) {         array->array[size] = val;         printf("array[%d]====%d\n", size, array->array[size - 1]);         array->size++;     } }   int main() {     int i;     myarray *da = create();     //printf("da->size = %d\nda->length = %d\n",da->size,da->length);      (i = 0; i<12; i++)         add(da, i);     // printf("a->size = %d\nda->length = %d\n",da->size,da->length);     (i = 0; i<12; i++)         printf("the no.%i %d\n", i, da->array[i]); } 

as said in comments, you're misusing realloc , not editing length correctly. here's add should be:

void add(myarray *array, int val){     int length = array->length;     int size = array->size;      if(size == length){         array->length *= 2;         array->array=(int*)realloc(array->array,sizeof(int)*length);     }     array->array[size] = val;     array->size++; }