typedef struct mystruct {
int* a;
float** b;
} mystruct;


mystruct* s = (mystruct*) calloc(1, sizeof(mystruct));
s->a  = (int*) calloc(100, sizeof(int));
s->b  = (float**) calloc(100, sizeof(float*));

for (int i=0; i<100; i++)
s->b[i]  = (float*) calloc(100, sizeof(float));

#pragma omp parallel for  shared(s) schedule(auto)

int *p;

#pragma omp parallel private(p)
{
   ...
}

#pragma omp parallel
{
   int *p;
   ...
}

int *a = malloc(10 * sizeof(int));

#pragma omp parallel private(a)
{
   a[1] = ... // <--- WRONG - no memory allocated automatically by OpenMP
}

#pragma omp parallel
{
    int *a = malloc(10 * sizeof(int));
    ...
    free(a);
}