computers and programming the 6 th lecture jiří Šebesta
TRANSCRIPT
Computers and programming
The 6th lecture
Jiří Šebesta
TOPIC
1. Structures2. Unions 3. Enumerative type4. Dynamic variables - introduction5. Example
Structures (1/4)
• Structure: an array consisting of items of different types embedding into superior type
typedef struct friends // my girlfriend{ char fname[20]; // her first name
char sname[20]; // her surrname int age; // her age char phone[20]; // her phone number
} T_friend;
• Declaration
type identifier
Structures (2/4)
int main(void){ T_friend baby;
strcpy(baby.fname, "Anna\0"); strcpy(baby.sname, "Novakova\0"); baby.age = 16; strcpy(baby.phone, "+420776151443\0");
printf(" %s %s - %d let - tel.: %s", baby.fname, baby.sname, baby.age, baby.phone);
getchar(); return 0;}
• Access to item of structure:
Source code: Ex59.c variable item
Structures (3/4)
typedef struct date // date{ int year; // year
int month; // month int day; // day} T_date;typedef struct drivelog // drive log book{ char driver[20]; // name
char in_city[20];// initial citychar en_city[20];// ending city
T_date in_date; // initial dateT_date en_date; // ending dtaint dist; // distanceint in_tacho; // initial st. of tacho.int en_tacho; // ending st. of tacho.
} T_drivelog;
• Structure in structure:
Structures (4/4)
T_drivelog toyota020, toyota021;
strcpy(toyota020.driver, "John");toyota020.in_date.year = 2011;toyota020.in_tacho = 53210;toyota020.en_tacho = 53372;toyota020.dist = toyota020.en_tacho-toyota020.in_tacho;
strcpy(toyota021.driver, "Judith");strcpy(toyota021.in_city, toyota020.en_city);toyota021.in_tacho = toyota020.en_tacho;toyota021.en_tacho = 53712;toyota021.dist = toyota021.en_tacho-toyota021.in_tacho;
• Manipulation with items of structure:
Source code: Ex60.c
Unions (1/3)
• Union: it enables to save values of different types to a single variable (allocated common space in memory)
union u1 {int i; double d; char c;} U = {'u'};
name ofunion
list of union items
variable of declared type of unie
• Memory size allocated for the union is given by the size of the largest element
• STRUCTURE: int and double and char • UNION: int or double or char
Unions (2/3)
typedef union id // ID of item{ int id_num; // numerical ID char id_str[10]; // textual ID} T_id;
int main(void){ char input_id[10];
int n, t;
printf("\n\nInsert ID: ");gets(input_id); // get string from stdin…
• Declaration
type identifier variable of declared type
Unions (3/3)
t=0; // test if at least char is not digitfor(n=0; input_id[n]!='\0'; n++)
if (input_id[n]<'0' || input_id[n]>'9')t=1;
// t=0 input_id is a number, t=1 input_id is a stringif (t==0) // input_id is a number{
item.id_num=atol(input_id);printf("ID contents a number: %d\n", item.id_num);
}else // input_id is a string{
strcpy(item.id_str, input_id);printf("ID contents a string: %s\n", item.id_str);
}
S. code: Ex61.c
Enumerative type (1/3)
• Enumerative type: a set of symbolic constants with strictly defined values
enum cards {seven, eight, nine, face_card, ace} set_1, set_2;
enum cards {seven=7, eight, nine, face_card=20, ace=30} set_1, set_2;
• Declaration:
type identifier variable of declared type
0 1 2
3 4
7 8 9
20 30
Enumerative type (2/3)
• Operator for enumerative type:– only assignment
enum cards {seven=7, eight, nine, face_card=20, ace=30} set_1, set_2;
set_1 = nine;
set_2 = 8; //not possible, 8 isn’t enumerator
set_1 -=2; //not possible
int num = seven //type cast of enumerator seven to int
Enumerative type (3/3)
enum zodiac {aries,taurus,gemini,cancer,leo,virgo, libra, scorpio, sagittarius, capricorn, …} eva;eva = virgo;
switch(eva){ case aries: printf(”She is hard-headed”); break; case taurus: printf(”She is reserved”); break; case gemini: printf(”She is friendly”); break; case cancer: printf(”She is anxious”); break; case leo: printf(”She is bossy”); break; case virgo: printf(”She is trusty”); break; case libra: printf(”She is shaky”); break; … }
Source code: Ex62.c
Dynamic variables – intro (1/3)
• Static variable: – memory space allocation when program is starting– memory space release when program is closing
• Dynamic variable: – controlled memory space allocation when program is running by function malloc() in C– controlled memory space release when program is running by function free() in C
Dynamic variables – intro (2/3)
• Application of dynamic variables: – a memory space can be allocated and released if program is running any time– suited for large blocks of data (e.g. large arrays), which are temporal (e.g. results, which will not be used later)– if we work with unknown size of array, if we use a static variable, we have to allocate the space for the worst case (max. size), e.g. double x[10000] , this space is permanently blocked (in given function)
Dynamic variables – intro (3/3)
#include <stdio.h>#include <stdlib.h>
int main( void){ double *x, y; x = (double*)malloc(sizeof(double)); *x = 3.14; y = *x; free(x); printf("Ludolf's number: %f", y); printf("Ludolf's number: %f", *x); //free(x); getchar(); return 0;}
free address
free variable
void *malloc(size_t size)
type cast
space release in memory pointed by x
this space in a memory is pointed by x
allocation of space in a memory with size of double
Source code: Ex63.c
Example (1/5)
• Create a program working as a car database. Each car is described by a type and a year of production. Data of cars are saved in dynamic variables, pointers are stored in an array. Adding a car is activated by pressing the key A, deleting by pressing D, and the program is stopped by pressing Q. In the database, at least one car has to be left.
#include <stdio.h>#include <stdlib.h>#include <string.h>typedef struct car // car record{ char type[10]; int year;} T_car; T_car *my_cars[20]; // ptrs. to cars - globalint cnt=0; // recorded cars - global
void addcar(char *atype, int ayear){ T_car *car; // pointer to a car
car = (T_car*)malloc(sizeof(T_car)); strcpy(car->type, atype); // notation 1 (*car).year = ayear; // notation 2 my_cars[cnt++] = car;}
Example (2/5)
void showdelcar(void){ printf("type: %s\n", my_cars[cnt]->type); printf("year: %d\n", my_cars[cnt]->year);}
Function which adds a car
Function which displays erased car
void erasecar(void){ if(cnt>1) // if at least two cars { cnt--; // one car to be removed showdelcar(); // print the removed car free(my_cars[cnt]); // delete last } else printf("All cars can’t be deleted");}
Example (3/5)
Function which deletes a car
int main(void){ char cmd, my_type[12]; int my_year;
printf("\nA: Add, D: Delete, Q: Quit\n"); scanf("%c", &cmd); fflush( stdin); while(!(cmd == 'Q' || cmd == 'q')) { if(cmd=='A' || cmd=='a') { printf("\ntype : "); scanf("%s", &my_type); fflush(stdin); printf("\nyear : "); scanf("%d", &my_year); fflush(stdin); add(my_type, my_year); }
Example (4/5)
Main function - beginning
if( cmd=='D' || cmd=='d') erasecar();
printf("\nA: Add, D: Delete, Q: Quit"); scanf("%c", &cmd); fflush(stdin); } return 0;}
Example (5/5)
Main function - conclusion
Source code: Ex64.c
TOPIC OF THE NEXT LECTURE
Programming with files
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