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Enums

typedef enum Weekday {
    Sunday, 
    Monday, 
    Tuesday, 
    Wednesday, 
    Thursday, 
    Friday, 
    Saturday
} Weekday;
Weekday today = Wednesday;
printf("Day %d",today+1); 
printf("Size of enum variable = %d bytes", 
        sizeof(today));

Enums : Changing default values

typedef enum Weekday {
    Sunday = 1, 
    Monday, 
    Tuesday, 
    Wednesday, 
    Thursday, 
    Friday, 
    Saturday
} Weekday;
Weekday today = Wednesday;
printf("Day %d",today+1);

Enums : interchangable with int

typedef enum Weekday {
    Sunday = 1, 
    Monday, 
    Tuesday, 
    Wednesday, 
    Thursday, 
    Friday, 
    Saturday
} Weekday;
Weekday today = 100;
printf("Day %d",today+1);

Add Payment Mode to Reciept

Payment Mode as int

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

Problem

  • We have to remember that
    • 0 is for cash,
    • 1 is for card,
    • 2 is for upi
  • Code will contain these magic numbers, which might not be obvios to another person.

Enum

typedef enum PayMode {
    Cash = 0,
    Card = 1,
    UPI = 2
} PayMode;

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

Strings in C

  • as a pointer to char
char *p = "abcde";
  • as an array of char
char s[] = "abcde";

print("%d %d", sizeof(p), sizeof(s));

String Functions

#include <string.h>

  • int strlen(char *s): returns the length of the string pointed by s (ie lenth upto the first \0 in memory).
  • char* strcat(char* s1, char* s2): concatenates s1 with s2, stores it in s1 and returns s1.
  • int strcmp(char *s1,char *s2): returns negative int if s1 is lex. smaller than s2, returns 0 if equal, returns positive int if s1 is lex. greater than s2.
  • char* strcpy(char* s1, char* s2): copies s2 in to s1 and returns s1.

Social Network

Name Age Status Friends
Alice 24 Single Diestel, Eve
Bob 28 Maried Alice
Charlie 20 Single Diestel
Diestel 27 Not Mentioned Alice, Eve, Charlie
Eve 25 Engaged Diestel, Alice

Define a Person (Profile)

enum RelStatus {
    NotMentioned,
    Single,
    Engaged,
    Married
};

struct Person {
    char name[100];
    int age;
    enum RelStatus status;
};

How to define the friends list?

Friends List

struct Person {
    char name[100];
    int age;
    enum RelStatus status;
    int count_friends;
    struct Person friends[5];
};
  • Will this work?
  • What is the sizeof(p) where p has type Person?

Recursive Type Definition with Pointers

struct Person {
    char name[100];
    int age;
    enum RelStatus status;
    int count_friends;
    struct Person *friends[5];
};

How to represent a Social Network?

How to represent a Social Network?

typedef struct SocialNet {
    struct Person members[100];
    int size;
} SocialNet;

Build a Social Network

Name Age Friends
Alice 24 Diestel, Earl
Bob 28 Alice
Charlie 20 Diestel
Diestel 27 Alice, Earl, Charlie
Earl 25 Diestel, Alice