Pointer
Hi everyone, I am still having a few small problems understanding some of the rules of C. I've successfully converted a program from C++ to C with the help of a book. Unfortunately there is one part that I do not understand. i understand the concept somewhat but does not make much sense. For example
[code]
if ((*Group).Packs.Climb.Num > 4)
{
(*Group).Packs.Climb.Discount = (*Group).Packs.Climb.Charges * .10;
(*Group).Packs.Climb.Charges -= (*Group).Packs.Climb.Discount;
}
else
(*Group).Packs.Climb.Discount = 0;
[\code]
My question is why do I need the paranthesis around pointer group. In C++ I would not need the paranthesis or the pointer but I tried to write it in c using -> but received an error. The way I saw it written in the book was written with the paranthesis but I do not want to complete the program before I completely understand why? I receive an illegal inderection error when I use *Group->Packs.Climb.Charges * .10; or if I remove the paranthesis. Please let me know if it is something simple of if there is a book that goes deep into C programming so that I can understand this better
**I've included more code below just in case you need to see it**
Code:#include<iostream.h> #include <iomanip.h> #include<stdio.h> //The data structures struct Package1 //Climbing package { int Num; //Number in party int Beginners; //Those needing instructions int Advanced; //Those not needing instructions int NeedEquip; //Those renting camping equipments float BaseCharges; //Base charges float Charges; //Total charges float Instruction; //Cost of instruction float Equipment; //Cost of equipment rental float Discount; //Discount float Deposit; //Required deposit }; struct Package2 //Scuba package { int Num; //Number in party int Beginners; //Those needing instructions int Advanced; //Those not needing instructions float BaseCharges; //Base charges float Charges; //Total charges float Instruction; //Cost of instruction float Discount; //Discount float Deposit; //Required deposit }; struct Package3 //Sky Diving Package { int Num; //Number in party int Lodge1; //Number at 1st lodging choice int Lodge2; //Number at 2nd lodging choice float BaseCharges; //Base charges float Charges; //Total charges float Discount; //Discount float Lodging; //Cost of lodging float Deposit; //Required deposit }; struct Package4 //Spelunking Package { int Num; //Number in party int NeedEquip; //Those renting camping equipments float BaseCharges; //Base charges float Charges; //Total charges float Equipment; //Cost of equipment rental float Discount; //Discount float Deposit; //Required deposit }; union Pack //Combines all four structs { struct Package1 Climb; struct Package2 Scuba; struct Package3 Sky; struct Package4 Spel; }; struct Reservation { int PackNum; //Indicates which package is stored union Pack Packs; //All Structs are combined into union Pack and passed on to Packs }; //Constants for the charges const float ClimbRate = 350.0; //Base rate - Devil's Courthouse const float ScubaRate = 1000.0; //Base Rate - Bahamas const float SkyDiveRate = 400.0; //Base Rate - Sky diving const float CaveRate = 700.0; //Base Rate - Spelunking const float ClimbInstruct = 100.0; //Climbing instructions const float ScubaInstruct = 100.0; //Scuba instructions const float DailyCampRental = 40.0; //Daily camping equip. rental const float DayLodge1 = 65.0f; //Lodging option (sky diving) const float DayLodge2 = 120.0f; //Lodging option (sky diving) //Function prototypes void Climbing(struct Reservation*); void Scuba(struct Reservation*); void SkyDive(struct Reservation*); void Spelunk(struct Reservation*); int Menu(void); void DisplayInfo(const struct Reservation*); void DisplayPack1(const struct Reservation*); void DisplayPack2(const struct Reservation*); void DisplayPack3(const struct Reservation*); void DisplayPack4(const struct Reservation*); //Main function main() { int Selection; struct Reservation Group; do { Selection = Menu(); switch (Selection) { case 1: Climbing(& Group); break; case 2: Scuba(& Group); break; case 3: SkyDive(& Group); break; case 4: Spelunk(& Group); break; case 5: printf("Exiting program.\n\n"); //(cout had been changed to printf for c conversion) } if (Selection <5) DisplayInfo(& Group); } while (Selection != 5); return 0; } //Definition of function Menu. //Displays the main menu and asks the user to select an option. //Returns an integer in the range 1 - 5. int Menu(void) { int Choice; do { printf("\nHigh Adventure Travel Agency\n"); printf("------------------------------\n"); printf("1) Devil's Courthouse Adventure Weekend\n"); printf("2) Scuba Bahama\n"); printf("3) Sky Dive Colorado\n"); printf("4) Barron Cliff Spelunk\n"); printf("5) Exit program\n\n"); printf("Enter 1, 2, 3, 4, or 5: "); scanf("%d", &Choice); //(cin has been changed to scanf for c conversion) if (Choice < 1 || Choice > 5) //If choice is less than 1 or greater than 5 printf("Invalid Selection\n"); //Cout/printf "Invalid Selection } while (Choice < 1 || Choice > 5); //????????????? return Choice; } //Definition of Climbing function. // Uses a Reservation reference parameter to hold the vacation // package information. This function calculates the charges for // the Devil's Courthouse Adventure Weekend package. void Climbing(struct Reservation *Group) { (*Group).PackNum= 1; printf("\nDevil's Courthouse Adventure Weekend\n"); printf("--------------------------------------\n"); printf("How many will be going who need an instructor? "); scanf("%d", &(*Group).Packs.Climb.Beginners); printf("How many advanced climbers will be going? "); scanf("%d", &(*Group).Packs.Climb.Advanced); (*Group).Packs.Climb.Num =(*Group).Packs.Climb.Beginners + (*Group).Packs.Climb.Advanced; printf("How many will be rent camping equipment? "); scanf("%d", &(*Group).Packs.Climb.NeedEquip); //Calculate base charges (*Group).Packs.Climb.BaseCharges = (*Group).Packs.Climb.Num * ClimbRate; (*Group).Packs.Climb.Charges = (*Group).Packs.Climb.BaseCharges; //Calculate 10% discount for 5 or more if ((*Group).Packs.Climb.Num > 4) { (*Group).Packs.Climb.Discount = (*Group).Packs.Climb.Charges * .10; (*Group).Packs.Climb.Charges -= (*Group).Packs.Climb.Discount; } else (*Group).Packs.Climb.Discount = 0; }
