Values displayed after realloc are weird - c

Question

I called malloc and then I want to cut size in half using realloc when i display values of relocated malloc few numbers shows as 0, is that normal or I messed something up?
double main()
{
double *test;
int size = 10;
int sizes;
int i = 0;
double value;
test = (double*)malloc(size*sizeof(double));
if(test == NULL)
{
printf("ERROR");
return 0;
}
else
{
printf("\nInsert values : \n");
for(i=0;i<=size;)
{
scanf("%lf",&*(test+i));
if(*(test+i)==0.0)
{
break;
}
if(i>=size)
{
size=size+2;
test = realloc(test, size*sizeof(double));
}
i++;
}
}
sizes=size/2;
test = realloc(test, sizes*sizeof(double));
printf("\nSaved values : \n");
for(i=0;i<size;i++)
{
printf("%lf\n",*(test+i));
}
}
I want to learn some coding so please tell me if and what I am doing wrong.

Answer 1

If I well understand you stop to read value at EOF or when the read value is 0, and 0 is not memorized, and when the read is done you want to reduce the allocates vector to the minimal size, in that case :
#include <stdlib.h>
#include <stdio.h>
int main()
{
int size = 10;
double *test = malloc(size*sizeof(double));
if(test == NULL)
{
printf("ERROR");
return 0;
}
else
{
int i = 0;
double value;
printf("\nInsert values : \n");
while ((scanf("%lf",&value) == 1) && (value != 0))
{
if (i >= size) /* == is enough */
{
size += 2; /* I add 2 entries as you */
test = realloc(test, size*sizeof(double));
}
test[i++] = value;
}
/* remove possible extra entry at the end */
if (i != size)
test = realloc(test, i*sizeof(double));
size = i;
printf("\nSaved values : \n");
for(i=0 ;i<size; ++i)
{
printf("%lf\n",test[i]);
}
free(test);
}
return 0;
}

Answer 2

Two issues here:
This
for(i=0;i<=size;)
makes this
scanf("%lf",&*(test+i));
scan into memory one element beyond the allocated memory on the last iteration before reallocating. Doing so invokes undefined behaviour. Already from now on anything may happen.
Those two lines
sizes=size/2;
test = realloc(test, sizes*sizeof(double));
shrink the valid memory to the half of its size, and then this loop
for(i=0;i<size;i++)
{
printf("%lf\n",*(test+i));
}
tries to read out the second half's value which just had been shrinked away. This half's memory is not valid any more. Trying to read it invokes undefined behaviour as well.
So to answer your question:
or i messed something up
Yes you did, namely by invoking undefined behaviour. Do not do that.