Loop Gets Stuck at Particular Index

I'm using the TM4C1294XL board with CCS. The following code gets stuck at iteration number 255 ( i.e. when TestTempInt = 255).

Array x_frame;
InitNullArray(&x_frame);

for(TestTempInt=n;TestTempInt<=(n+499);TestTempInt++){
AddConsToArr(&x_frame,X[TestTempInt]);
printf("%d\n",TestTempInt);
}

The Array structure and Function declarations are as follows:

InitialArrayValue = -999;

typedef struct ArrayStruct{
    float * array;
    size_t used;
    size_t size;
}Array;

// INITIALIZE NULL ARRAY
void InitNullArray(Array * ArrayPtr){
    ArrayPtr->array=NULL;
    freeArray(ArrayPtr);
    ArrayPtr->array = (float *)malloc(1 * sizeof(float));
    ArrayPtr->used = 0;
    ArrayPtr->size = 1;
    ArrayPtr->array[0] = InitialArrayValue;
}

// ADD CONSTANT TO ARRAY ( A=[A;C] )
void AddConsToArr(Array * InitialArray, float NewValue){
    insertArray(InitialArray,NewValue);
}

// INSERT ELEMENT INTO ARRAY
void insertArray(Array *a, float element) {
    if (a->used+1 == a->size) {
        a->size *= 2;
        a->array = (float *)realloc(a->array, a->size * sizeof(float));
    }
    a->array[(a->used)+1] = element;
    a->used=a->used+1;
}

Is this a matter of Heap or Stack size ? If so, how much can I allocate to each ? If not, what other thing should I be looking at. Please advise. Thank you.

P.S: The Array Structure itself is made so that it mimics the array indexing used in MATLAB.