#include <stdio.h>

void manipulate(double *a)
{
    printf("before: a = %f\n", *a);
    *a = 9.9;
    printf("after: a = %f\n", *a);
}

int main()
{
    double number = 0.0;

    printf("before minupulate: number = %f\n", number);

    manipulate(&number);

    printf("after minupulate: number = %f\n", number);

    return 0;
}