Post on 02-Jan-2016
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Structures, ADT
Lecture 2514/3/2002
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Announcements Lab Test 2 on the week of 18th –
22nd March Syllabus for lab test : arrays,
structures, data types, …..
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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The List ADT A list : <A1, A2, ... , AN> of size N. Special list of size 0 : an empty list Operations:
makenull () : returns an empty list makelist (elem) : makes a list containing a single
element printlist (list) search(elem, list) : searches whether a key is in
the list insert (elem, list) delete (elem, list) findKth (list)
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Array Implementation of Listtypedef int ETYPE;typedef struct {
ETYPE elements[MAXS];int size;
} LIST;LIST makenull () ;LIST makeList (ETYPE) ;void printList (LIST) ;int IsEmpty (LIST) ;int search (ETYPE, LIST) ;void delete (ETYPE, LIST * );void insert (ETYPE, LIST * )
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Complex Number ADTtypedef struct {
float real;float imag;
} COMPLEX;COMPLEX makecomplex (float, float) ;COMPLEX addc (COMPLEX, COMPLEX);COMPLEX subc (COMPLEX, COMPLEX);COMPLEX multc (COMPLEX, COMPLEX);COMPLEX divc (COMPLEX, COMPLEX);
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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SET ADT Interface functions (1):SET makenullset () ;int member (ETYPE, SET)
;SET adjoin (ETYPE, SET);SET union (SET, SET) ;SET intersection (SET,
SET);Void printset (SET) ;
Interface functions (2):SET makenullset () ;int member (ETYPE, SET) ;void adjoin(ETYPE, SET *);void union (SET, SET, SET*);void intersection (SET, SET, SET*);Void printset (SET) ;
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Concrete implementation of SET ADT
typedef struct {ETYPE elem[MAX];int size;
} SET;
Implementation 1 : sorted arrayadjoin : Sorted insertmember : Binary searchdelete : ?union : merge 2 sorted arrays intersection : ?
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Concrete implementation of SET ADT
typedef struct {ETYPE elem[MAX];int size;
} SET;
Implementation 2 : unsorted arraykeep the elements in the array unsorted.
adjoin : Insert at the endmember : Search till found or till the enddelete : Go through the array sequentially until
element is found, or reach the end.Then left shift the array.
union , intersection ?
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Arrays of Structures A struct represents a single record. Typically structs are used to deal with
collections of such records Examples : student records, employee
records, book records, ... In each case we will hav multiple instances
of the struct type.Arrays of structs are the natural way to do
this.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Arrays of structs : declaration & use
Each declaration below declares an array, where each array element is a structure:point corner_points[10] ;StudentRecord btech01[MAXS] ;
We access a field of a struct in an array by specifying the array element and then the field :btech01[i].namecorner_points[4].x
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Naming in struct Arrayspoint pentagon[5];
xy
xy
xy
xy
xy
pentagon : an array of points
pentagon[1] : a point structure
pentagon[4].x : a double
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Using Arrays of structs
StudentRecord class[MAXS];...for (i=0; i<nstudents; i++) {
scanf (“%d%d”, &class[i].midterm, &class[i].final);
class[i].grade = (double)(class[i].midterm+class[i].final)/50.0;
}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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struct Array elements as parameters
void draw_line (point p1, point p2) { ... }...point pentagon[5];...for (i=0;i<4;i++)
draw_line (pentagon[i], pentagon[i+1]);
draw_line (pentagon[4], pentagon[0]);
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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structs as Parameters
A single struct is passed by value. all of its components are copied from
the argument (actual parameter) to initialize the (formal) parameter.
point set_midpt (point a, point b) { ... }int main (void) {
point p1, p2, m;...m = set_midpt(p1, p2);
}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Passing Arrays of structs An array of structs is an array. When any array is an argument (actual parameter), it
is passed by reference, not copied [As for any array] The parameter is an alias of the actual array
argument.int avg (StudentRec class[MAX]) { ... }int main (void) {
StudentRec bt01[MAX];int average;...average = avg_midpt(bt01) ;
}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Dynamic Memory Allocation,Structure pointers
Lecture 2614.3.2002.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Basic Idea Many a time we face situations where
data is dynamic in nature. Amount of data cannot be predicted
beforehand. Number of data item keeps changing
during program execution. Such situations can be handled more
easily and effectively using dynamic memory management techniques.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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C language requires the number of elements in an array to be specified at compile time. Often leads to wastage or memory
space or program failure. Dynamic Memory Allocation
Memory space required can be specified at the time of execution.
C supports allocating and freeing memory dynamically using library routines.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Memory Allocation Process in C
Local variables
Free memory
Global variables
InstructionsPermanent storage area
Stack
Heap
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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The program instructions and the global variables are stored in a region known as permanent storage area.
The local variables are stored in another area called stack.
The memory space between these two areas is available for dynamic allocation during execution of the program. This free region is called the heap. The size of the heap keeps changing
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Memory Allocation Functions
malloc: Allocates requested number of bytes and returns a pointer to the first byte of the allocated space.
calloc: Allocates space for an array of elements, initializes them to zero and then returns a pointer to the memory.
free : Frees previously allocated space. realloc: Modifies the size of previously
allocated space.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Dynamic Memory Allocation used to dynamically create
space for arrays, structures, etc.
int main () { int *a ; int n; .... a = (int *) calloc (n, sizeof(int)); ....}
a = malloc (n*sizeof(int));
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Space that has been dynamically allocated with either calloc() or malloc() does not get returned to the function upon function exit.
The programmer must use free() explicitly to return the space. ptr = malloc (...) ; free (ptr) ;
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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void read_array (int *a, int n) ;int sum_array (int *a, int n) ;void wrt_array (int *a, int n) ;
int main () { int *a, n; printf (“Input n: “) ; scanf (“%d”, &n) ; a = calloc (n, sizeof (int)) ; read_array (a, n) ; wrt_array (a, n) ; printf (“Sum = %d\n”, sum_array(a, n);}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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void read_array (int *a, int n) { int i; for (i=0; i<n; i++)
scanf (“%d”, &a[i]) ;}void sum_array (int *a, int n) { int i, sum=0; for (i=0; i<n; i++) sum += a[i] ; return sum;}void wrt_array (int *a, int n) { int i; ........}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Arrays of Pointers Array elements can be of any type
array of structures array of pointers
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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int main (void) {char word[MAXWORD];char * w[N]; /* an array of pointers */int i, n; /* n: no of words to sort */
for (i=0; scanf(“%s”, word) == 1); ++i) { w[i] = calloc (strlen(word)+1, sizeof(char)); if (w[i] == NULL) exit(0);
strcpy (w[i], word) ;}
n = i;sortwords (w, n) ;wrt_words (w, n);return 0;
}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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w
0
1
2
3
17
Input : A is for apple or alphabet pie which all get a slice of come taste it and try
A \0
i s \0
f o r \0
a p p l e \0
t r y \0
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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void sort_words (char *w[], int n) { int i, j; for (i=0; i<n; ++i)
for (j=i+1; j<n; ++j)if (strcmp(w[i], w[j]) > 0) swap (&w[i], &w[j]) ;
}void swap (char **p, char **q) { char *tmp ; tmp = *p; *p = *q; *q = tmp;}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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w
w[i]
f o r \0
a p p l e \0
Before swapping
w[j]
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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w
w[i]
f o r \0
a p p l e \0
After swapping
w[j]
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Pointers to Structure
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Pointers and Structures You may recall that the name of an array
stands for the address of its zero-th element. Also true for the names of arrays of structure
variables. Consider the declaration:
struct stud { int roll; char dept_code[25]; float cgpa; } class[100], *ptr ;
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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The name class represents the address of the zero-th element of the structure array.
ptr is a pointer to data objects of the type struct stud.
The assignmentptr = class ;
will assign the address of class[0] to ptr. When the pointer ptr is incremented by
one (ptr++) : The value of ptr is actually increased
by sizeof(stud). It is made to point to the next record.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Once ptr points to a structure variable, the members can be accessed as: ptr –> roll ; ptr –> dept_code ; ptr –> cgpa ;
The symbol “–>” is called the arrow operator.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Warning When using structure pointers, we should
take care of operator precedence. Member operator “.” has higher precedence than “*”.
ptr –> roll and (*ptr).roll mean the same thing. *ptr.roll will lead to error.
The operator “–>” enjoys the highest priority among operators.
++ptr –> roll will increment roll, not ptr. (++ptr) –> roll will do the intended thing.
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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Program to add two complex numbers using pointers
typedef struct { float re; float im;} complex;main() { complex a, b, c; scanf (“%f %f”, &a.re, &a.im); scanf (“%f %f”, &b.re, &b.im); add (&a, &b, &c) ; printf (“\n %f %f”, c,re, c.im);}
14/3/02 Sudeshna Sarkar, CSE, IIT Kharagpur
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void add (complex * x, complex * y, complex * t) {
t->re = x->re + y->re ;
t->im = x->im + y->im ;
}