Thread: Function arguments

Can someone explain to me why this bit of code works and the commented version of double functest doesnt. dont understand functions very well it seems...
insert

Code:

/*****START**/

#include<stdio.h>
#include<stdlib.h>
typedef struct
{
    //
    double test1;
    double test2;
}t;
t tab;
t * q = &tab;
double functest(void);
int main()
{
    //
    printf("enter test1\t");
    scanf("%lg",&q->test1);
    printf("\nenter test2\t");
    scanf("%lg",&q->test2);
/*    printf("hence function returns %lg",functest(q->test1,q->test2));*/
    printf("hence function returns %lg\n",functest());
    return 0;
}


/*double functest(double q->test1,double q->test2)*/
/*{*/
/*    return q->test1 * q->test2;*/
/*}*/


double functest(void)
{
    double res;
    res=q->test1*q->test2;
    printf("answer is%lg",res);
    return res;


}
/****END***/

How do you provide arguments to a function where the variable is in a struct???

Thanks for your help