Example

int main(int argc, char* argv[])
{
int array[] = {0,1,2};
int index = 1;

array[index] = ++index;

return 0;
}

Solution
Do not modify the index variable when using it to access an array.

int main(int argc, char* argv[])
{
int array[] = {0,1,2};
int index = 1;

array[index] = index + 1;
index ++;

return 0;
}