slides.md

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C Prog.

Lec 6

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Problem

• Write a program for cashier of a store.
  • The program should keep the data regarding each customer and reciepts.
  • It should be able find total revenue for any time frame.
  • It should be able to list out chronologically sorted list of reciepts for a particular customer.

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How to store Data?

• Customer has a

  • Phone No.
  • Name

• Reciept has a

  • date time
  • value
  • customer

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How to store a single Customer Data?

typedef struct Customer {
    char name[100];
    int phone_no;
} Customer;

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How to store a single Reciept

Use time_t from time.h https://en.cppreference.com/w/c/chrono/time_t

typedef struct Reciept {
    time_t time;
    float value;
    Customer *customer;
} Reciept;

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How to store of all the customers and reciepts

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typedef struct Database {
    Customer customers[100];
    Reciept reciepts[1000];
} Database;

• Assuming max customers < 100 and reciepts < 1000.

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Problem

• Suppose we need to add a new customer, where should it go?
• How many customers are there currently?

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Solution

typedef struct Database {
    Customer customers[100];
    Reciept reciepts[1000];
    int customer_count;
    int reciept_count;
} Database;

• customer_count stores the current number of customers. New customers are added to the customers[customer_count] and customer_count is incremented.

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Wrong

Customer* add_customer(char *name, 
                        int phone_no, 
                        Database *db) {
    Customer c = db->customers[db->customer_count];
    c.phone_no = phone_no;
    c.name = name;
    db->customer_count++;
    return c;
}

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Right approach

Customer* add_customer(char *name, 
                        int phone_no, 
                        Database *db) {
    Customer *c = 
      &(db->customers[db->customer_count]);
    c->phone_no = phone_no;
    strcpy(c->name, name);
    db->customer_count++;
    return c;
}