void func_Add(double *result)
{
    double arg1 = 0;
    double arg2 = 0;

    prepearData(&arg1, &arg2);
    printf("nEntered arguments: %lf and %lfn", arg1, arg2);
    *result = arg1 + arg2;
    printf(">>Addition result: %lf n", *result);
}

void prepearData(double *arg1, double *arg2)
{
        printf(">> Enter FIRST argument:");
        scanf("%lf", &arg1);
        printf(">> Enter SECOND argument:");
        scanf("%lf", &arg2);
        printf("prepearData: %lf and %lfn", arg1, arg2);
}

void prepearData(double *arg1, double *arg2)
{
        printf(">> Enter FIRST argument:");
        scanf("%lf", arg1);
        printf(">> Enter SECOND argument:");
        scanf("%lf", arg2);
        printf("prepearData: %lf and %lfn", *arg1, *arg2);
}

scanf("%lf", arg1);
. . .
printf("prepearData: %lf and %lfn", *arg1, *arg2);