Senem KUMOVA METİN CS FALL 1 POINTERS && ARRAYS CHAPTER 6

Senem KUMOVA METİN CS FALL 2 POINTERS POINTER is a programming language data type whose value refers directly to (or "points to") another value stored elsewhere in the computer memory using its address

Senem KUMOVA METİN CS FALL 3 POINTERS  int x= 5 is a variable and 5 is the value of it printf(“value of x : %d”, x); &x is the location or address of the x printf(“address of x in memory : %d”, &x);  Pointers are declared in programs and then used to take addresses !!! int x=5; // some stored value int * p; // a pointer that can hold the address of an integer p=&x; x= 5 &x …. ….. MEMORY

Senem KUMOVA METİN CS FALL 4 Pointers: & operator 5 0x x int x = 5; p int *p; p = &x; // adress of x is // stored in p 0x p is a pointer: it contains the address of a piece of data Memory Address &x

Senem KUMOVA METİN CS FALL 5 POINTERS int * p; // A pointer that can hold an address // of an integer  integer pointer int a =0; p= &a; double * q // A pointer that can hold an address // of a double  double pointer double b=1.2; q= &b; char * t // A char pointer char c=‘D’; t = &c;

Senem KUMOVA METİN CS FALL 6 POINTERS main() { int * p; //  integer pointer int a =0; p= &a;//  a equals to *p printf(“%d \n”, a); printf(“%d \n”, *p); *p=6; printf(“%d \n”, a); printf(“%d \n”, *p); a++; printf(“%d \n”, a); printf(“%d \n”, *p);} a=0 p=&a *p

Senem KUMOVA METİN CS FALL 7 POINTERS int a=1, b=2, *p; p=&a; &a&b &p a=1 b=2 ?? will point somewhere in memory &p 1 2 p=&a &a&b

Senem KUMOVA METİN CS FALL 8 POINTERS b=*p; // equivalent to b=a &a &b&p a=1 b=1 ( the value of a ) p=&a THE VALUE POINTED BY A POINTER CAN BE CHANGED BY * name_pointer *p

Senem KUMOVA METİN CS FALL 9 Pointers : EXAMPLE 1 #include void main(void) { int i = 7, j=3, *k, *m; k = &i; // k ??? *k ??? j=*k; // k ??? *k ??? m=&i; // i ??? *i ??? (*m) ++; // m ??? *m ??? printf(“ %d %d %d %d”, i, j, *k, *m); }

Senem KUMOVA METİN CS FALL 10 Pointers : EXAMPLE 2 #include void main(void) { char a = ‘D’; char *p = &a; *p=*p+2; printf(“%c %c”, a, *p); a=a+1; printf(“%c %c”, a, *p);}

Senem KUMOVA METİN CS FALL 11 CALL BY VALUE /* Whenever variables are passed as arguments to a function, their values are copied to the function parameters */ void main() {int a=20; incr1 (a); printf(“%d: “, a); incr2 (a); printf(“%d: “, a);} void incr1(int x) { x++; } void incr2(int a) { a++; } R E M E M B E R !

Senem KUMOVA METİN CS FALL 12 CALL BY REFERENCE /* Pointers are passed as arguments to a function, their addresses are assigned to the function parameters defined as pointers:*/ void main() {int a=20; incr (&a); printf(“%d: “, a);} void incr(int * x) { (*x)++; }

Senem KUMOVA METİN CS FALL 13 CALL BY REFERENCE : Example 1 void addi(int *a, int b); void main() {int a=20, int b=30; addi (&a, b) printf(“%d %d :“, a, b);} void addi(int *a, int b) {int tmp = *a +b; *a= tmp; b= b++;} OUTPUT??

Senem KUMOVA METİN CS FALL 14 void main() {int a=20; int b=30; swap1 (a, b); swap2 (&a, &b); printf(“%d %d: “, a, b);} void swap1(int x, int y) {int tmp; tmp=x; x=y; y=tmp; } void swap2(int *x, int *y) {int tmp; tmp = *x; // get value pointed by x. *x = *y; // assign value pointed by y to x *y = tmp; } CALL BY REFERENCE Example 2 : SWAP

Senem KUMOVA METİN CS FALL 15 What is an Array?  int grade0, grade1, grade2;  int grade [3];  Arrays make it possible to represent large number of homogenous values grade0grade1grade2 grade[0]grade[1]grade[2]

Senem KUMOVA METİN CS FALL 16 One Dimensional Arrays  type name_of_array[size] EXAMPLE int grade[5]; data grade[1] data grade[2] data grade[0] grade[3] grade[4] MEMORY first element in array fift ( the last) element in array starts from 0 ends at size - 1

Senem KUMOVA METİN CS FALL 17 One Dimensional Arrays int grade[5], x=9, y; grade[0]= 0; grade[3]= 4; grade[2]= -1; grade[1]=grade[3]+grade[2]; grade[4]= x; x= grade[2]; y= grade[grade[3]]; 0 3 grade[1] grade[2] 4 9 grade[0] grade[3] grade[4] MEMORY x ? y ?

Senem KUMOVA METİN CS FALL 18 INITIALIZATION  float f1[]= { 1.0, 1.1, 1.2, 1.3 }; /* declaration without the size */  float f2[4]= { 1.0, 1.1, 1.2, 1.3 }; /* declaration with size */  char z[] =“abc”; // char arrays  char z[] = {‘a’, ‘b’, ‘c’, ‘\0’}  int a[80]={0};

Senem KUMOVA METİN CS FALL 19 EXAMPLE1: /* array1.c*/ main() { int x[10], k; for(k=0; k<10; k++) { x[k]=0; printf(“x[%d] = %d\n”, k, x[k]); //what will be the output ??? }

Senem KUMOVA METİN CS FALL 20 EXAMPLE2: /* array2.c*/ main() { int x[10], k; for(k=0; k<10; k++) { x[k]=k; printf(“x[%d] = %d\n”, k, x[k]); //what will be the output ??? }

Senem KUMOVA METİN CS FALL 21 EXAMPLE3: /* array3.c*/ main() { int x[10], k, sum=0; for(k=0; k<10; k++) scanf(“%d”, &x[k]); for(k=0; k<10; k++) { printf(“%d”, x[k]); sum=sum + x[k]; } printf(“sum is %d”, sum); }

Senem KUMOVA METİN CS FALL 22 Relationship between Pointers and Arrays /*An array name by itself is an adress or a pointer value */ int a[5], *p; p=&a[0]; // Equals to p=a;

Senem KUMOVA METİN CS FALL 23 Relationship between Pointers and Arrays &a[0] equals to a then a[0] equals to *a &a[1] equals to a+1 then a[1] equals to *(a+1) &a[2] equals to a+2 then a[2] equals to *(a+2) ……………………………………………………………………………… &a[i] equals to a+i then a[i] equals to *(a+i)  EXAMPLE: int a [5]={1,2,3,4,5}; int * p; printf(“%d”,a[0]); printf(“%d”,*a); printf(“%d”,a[2]); printf(“%d”,*(a+2)); p=&a[4]; P=a+4;

Senem KUMOVA METİN CS FALL 24 Relationship between Pointers and Arrays : Example1 main() { int x[10], k; for(k=0; k<10; k++) {x[k]=k; printf(“%d\n”, x[k]); } main() { int x[10], k; for(k=0; k<10; k++) { *(x+k)=k; printf(“%d\n”, *(x+k)); }

Senem KUMOVA METİN CS FALL 25 Relationship between Pointers and Arrays : Example2 main() { int x[10], k; for(k=0; k<10; k++) { *(x+k)=0; printf(“%d\n”, *x+k); } main() { int x[10], k; for(k=0; k<10; k++) { *(x+k)=0; printf(“%d\n”, *(x+k)); }

Senem KUMOVA METİN CS FALL 26 Pointer Arithmetic EXAMPLE double a[2],*p,*q; p=a; // p=&a[0] q=p+1; // q=&a[0]+1= &a[1] printf(“%d\n”, q-p); /* difference in terms of array elements */ printf(“%d\n”, (int) q-(int) p); /* difference in memory locations */

Senem KUMOVA METİN CS FALL 27 Arrays as Function Arguments main() { int x[9], r; r=sum(x,9); //sum(&x[0],9) } double sum( int a[], int n) { int i; double result =0.0; for (i=0; i<n; i++) result+=a[i]; return result; } main() { int x[9], r; r=sum(x,9); // sum(&x[0],9) } double sum( int * a, int n) { int i; double result =0.0; for (i=0; i<n; i++) result+=*(a+i); return result; }

Senem KUMOVA METİN CS FALL 28 Dynamic Memory Allocation  Calloc : contiguous memory allocation  Malloc : memory allocation

Senem KUMOVA METİN CS FALL 29 CALLOC  calloc(n, el_size)  an array of n elements, each element having el_size bytes int main() { int *a; //will be used as an array int n; // size of array.... a=calloc(n, sizeof(int)); /* get space for a, and initialize each bit to zero */ free(a); /* each space opened dynamically must be returned */ }

Senem KUMOVA METİN CS FALL 30 MALLOC /* malloc does not initialize memory */ int main() { int *a; //will be used as an array int n; // size of array.... a=malloc(n*sizeof(int)); /* get space for a */.... free(a); }

Senem KUMOVA METİN CS FALL 31 DYNAMIC ARRAY : Example main() { int * x, k,s; printf(“give array size”); scanf(“%d”,&s); x=malloc(s*sizeof(int)); for(k=0; k<s; k++)x[k]=k; for(k=0; k<s; k++)printf(“%d ”,x[k]); }

Senem KUMOVA METİN CS FALL 32 NEXT WEEK  MULTIDIMENSIONAL ARRAYS  SORTING ALGORITHMS : BUBBLE SORT MERGE SORT  STRINGS && STRING_HANDLING FUNCTIONS  ARRAYS OF POINTERS  ARGUMENTS TO MAIN