Embed Size (px)
DESCRIPTION
Structures
Citation preview
STRUCTURES
INTRODUCTION
oStructures are collection of related variables under one name
oThe variables can be from many data types
oCommonly used to defined records
oDerived data types which are constructed using intrinsic data types
Intrinsic data types
char, int, long,
float, double
Derived
struct
STRUCTURES DEFINITIONS struct Typename { StructureMemberDeclarationList; };
struct Student { char name[10]; int id; float test[2]; char grade; };
Tag
Type
Individual member
declarations
Ended with a semicolon
Good programming practice:
Tags begin with capital letters,
variables with small letters!
STRUCTURES DEFINITION
oKeyword struct introduces structure definition.
oStructure definition does not reserve any memory location
oStructure definition must end with a semicolon.
oMembers can be variables, pointers or arrays of primitive data types, it can also be other structures (nested structure) but not instance of itself
oHowever a member that is a pointer to the same structure is allowable
struct abc{ int member1;
struct abc member2;
};
struct abc{
int member1;
struct abc *member2;
};
Linked list –
ECP1026
NESTED STRUCTURES
oA structure can have members from different structures, but the members’ structure definition must be defined first
oEx.: Student record that contains record of registration date
StudentRec
name
id
dateReg
day
month
year
test
grade
struct Date
struct Student
struct Date {
int day;
char *month;
int year;
};
struct Student {
char name[10];
int id;
struct Date dateReg;
float test[2];
char grade;
};
STRUCTURES DECLARATION
oReserve memory
oSimilar to basic data type declaration
struct Student student1;
Variable name
Tag Type
Option 1 Option 2
struct Student {
char name[10];
int id;
float test[2];
char grade;
} student1;
struct {
char name[10];
int id;
float test[2];
char grade;
} student1;
STRUCTURES DECLARATION
oWe can also have array of structures
Lisa
101
82.5
90
A
Ali
102
76
68.75
B
Thomas
103
55.5
60
C
studentList
name
id
test test[0]
test[1]
grade
Components
struct Student studentList[3];
STRUCTURES INITIALIZATION
1. With declaration
oThe declaration is done with = and {}
oThe values of members are within the {} and separated by ,
oFor array of structure each record initial values should be grouped within {}
struct Student studentList[3] = {
{"Lisa", 101, {82.5, 90}, 'A'},
{"Ali", 102, {76, 68.75}, 'B'},
{"Thomas", 103, {55.5, 60}, 'C'}
};
2. After declaration
o Using structure member operator/dot operator
struct Student student1 = {"Lisa",101,{82.5,90},'A'};
ACCESSING MEMBERS OF STRUCTURES
strcpy(student2.name, "Ali"); student2.id = 102; student2.test[0] = 76; student2.test[1] = 68.75; student2.grade = 'B';
The dot operator
Assigned value
Member name
Variable name
ACCESSING MEMBERS OF STRUCTURES
oAccessing members of array of structures
Use both array notation and the dot operator
Example: Access the name of the student stored in the second element of the array studentList by writing
studentList[1].name
Lisa
101
82.5
90
A
Ali
102
76
68.75
B
Thomas
103
55.5
60
C
studentList
name
id
test test[0]
test[1]
grade
Components
ACCESSING MEMBERS OF STRUCTURE
oAccessing members of inner nested structure
Use the dot operator twice
Example:
studentRec.dateReg.month
StudentRec
name
id
dateReg
day
month
year
test
grade
struct Date
struct Student
TYPEDEF
oUsed to create synonyms for previously defined data types.
oUsed in structures for a shorter type name
typedef struct Typename { StructureMemberDeclarationList; } New_Typename;
typedef struct Typename New_Typename;
POINTERS TO STRUCTURES
oTo access members of structure variables using pointers
oTwo ways of accessing a structure member using a pointer:
1. The structure pointer operator, or the arrow operator (->)
Its syntax: structure_pointer->structure_member
2. The dereference operator (*) + dot operator (.) Its syntax: (*structure_pointer).structure_member
The parentheses is needed as the dot operator has a higher precedence than the pointer dereferencing operator
POINTERS TO STRUCTURES // Accessing structure variables using pointers
#include <stdio.h>
struct Complex{
double real;
double imag;
};
int main(){
struct Complex c1 = {1.2, 4.5}, c2 = {-3.1, 2.45}, sum;
struct Complex *cptr = &c2;
sum.real = c1.real + cptr->real;
sum.imag = c1.imag + (*cptr).imag;
printf("Sum = %+.2f%+.2fi\n", sum.real, sum.imag);
return 0;
}
PASSING STRUCTURES TO FUNCTIONS - CALL BY VALUE 1 // Accessing structure variables using pointers
#include <stdio.h>
struct Complex{
double real;
double imag;
};
int main(){
struct Complex c1 = {1.2, 4.5}, c2 = {-3.1, 2.45}, sum;
struct Complex *cptr = &c2;
sum.real = c1.real + cptr->real;
sum.imag = c1.imag + (*cptr).imag;
printf("Sum = %+.2f%+.2fi\n", sum.real, sum.imag);
return 0;
}
void comFunc1(double r ){
r += 10;
printf("In comFunc1: r = %.2f\n", r);
}
void comFunc2(struct Complex com){
com.real += 10;
com.imag += 5;
printf("In comFunc2: com.real = %.2f, "
"com.imag = %.2f\n", com.real, com.imag);
}
PASSING STRUCTURES TO FUNCTIONS - CALL BY VALUE 2 // Modifying a structure variable through a return #include <stdio.h> struct Complex{ double real; double imag; }; struct Complex comFunc(struct Complex); int main(){ struct Complex c = {1.25, 4.56}; // Assigning the return of the function call to the // variable to be modified c = comFunc(c); printf("c.real = %.2f, c.imag = %.2f", c.real, c.imag); return 0; } struct Complex comFunc2(struct Complex com) { com.real += 10; com.imag += 5; return com; }
PASSING STRUCTURES TO FUNCTIONS - CALL BY REFERENCE // Modifying structure variables using call-by-reference
#include <stdio.h>
struct Complex{
double real;
double imag;
};
typedef struct Complex Com;
void comSumProd(Com, Com, Com *, Com *);
int main(){
Com c1 = {1.2, 4.5}, c2 = {-3.1, 2.45}, sum, prod;
// Passing values of c1 and c2, and addresses of sum
// and prod to comSumProd
comSumProd(c1, c2, &sum, &prod);
printf("Sum = %.2f%+.2fi\n", sum.real, sum.imag);
printf("Prod = %.2f%+.2fi\n", prod.real, prod.imag);
return 0;
}
void comFunc1(Com c1, Com c2, Com *sptr, Com *pptr ){
(*sptr).real = c1.real + c2.real;
(*sptr).imag = c1.imag + c2.imag;
pptr->real = c1.real * c2.real - c1.imag * c2.imag;
pptr->imag = c1.real * c2.imag + c2.real * c1.imag;
}
EXERCISE
