2.  Recursion  Pointers and Arrays

3. #include void print3(int n){ if (n==0)return; printf ("%d\n",n); print3(n-1); printf ("%d\n",n); } void main(){ print3(5); }

4. #include void print4(int n){ if (n==0)return; print4(n-1); printf ("%d\n",n); print4(n-1); } void main(){ print4(4); }

5.  int is_even (unsigned int n) {  if (n==0) return 1;  else return (is_odd(n-1));  }  int is_odd (unsigned int n) {  return (!is_even(n));  }

6. int recFib(int n){ if(n<=1) return n; return recFib(n-1)+ recFib(n-2); }

7. int binSearch (int value, int from, int to, int Arr[]){ int middle = from+(to-from)/2; if (Arr[middle]==value) return middle; else if (from == to) return -1; else if (Arr[middle] < value) return binSearch (value, middle+1, to, Arr); else return binSearch (value, from, middle-1, Arr); }

8. void main(){ int a[10]={1,3,6,7,8,12,15}; int index; index =binSearch(6,0,7,a); if (index=-1) printf (“Element not found%d\n",index); else printf (“Element found at: %d place\n",index); }

9. {1, 3, 6, 7, 8, 12,15} f=0, t=7, m=3 {1, 3, 6} f=0, t=2, m=1 f=0, t=0, m=0 f=2, t=2, m=2 f=6, t=7, m=6 f=4, t=4, m=4 {7, 8, 12, 15} f=4, t=7, m=5

10. {1, 3, 6, 7, 8, 12,15} f=0, t=7, m=3 {1, 3, 6} f=0, t=2, m=1 f=0, t=0, m=0 f=2, t=2, m=2 f=6, t=7, m=6 f=4, t=4, m=4 f=4, t=7, m=5 f=0, t=2, m=1 {1, 3, 6, 7, 8, 12,15} f=0, t=7, m=3 f=2, t=2, m=2

11.  בתחילת המשחק מונחות הדיסקיות על עמוד אחד מסודרות לפי גודל  המטרה היא להעביר את כל הדיסקיות לעמוד האחרון  בכל צעד מותר להעביר דיסקית אחת, ואסור לשים דיסקית גדולה על קטנה

12. #include void moveDisk(int num, char from[], char to[]){ printf ("move disk %d from %s to %s\n", num,from,to); } void hanoi (int numDisks, char first[], char last[], char help[]){ if (numDisks == 1){ moveDisk(numDisks, first, last); } else{ hanoi(numDisks - 1, first, help, last); moveDisk(numDisks, first, last); hanoi(numDisks - 1, help, last, first); } void main(){ hanoi(3,"A","C","B"); }

13. Number of DisksNumber of Disks’ Moves 11 24 416 8256 1665,536 324,294,967,296 6418,446,744,073,709,600,000

14.  Pointers and Arrays

15. void main() { int a,b,*pa,*pb; a = 15; b = 20; pa = &a; b = *pa; *pa = 0; pb = &b; pa=pb; *pa=5; } MemoryAddresses 0 7663 5556 a: 5556 359 524 b: 524 2 8797 2015pa: 3028 3028 6080 15 5556 0 5 524 pb: 6080

16. #include void swap(int x, int y){ int temp=x; x=y; y=temp; } void main(){ int a=5,b=7; printf("a: %d, b: %d\n",a,b); swap(a,b); printf("a: %d, b: %d\n",a,b); }

17. #include void swap(int *x, int *y){ int temp=*x; *x=*y; *y=temp; } void main(){ int a=5,b=7; printf("a: %d, b: %d\n",a,b); swap(&a,&b); printf("a: %d, b: %d\n",a,b); }

18. #include void minmax(int x, int y, int *min, int *max){ if (x<y){ *min=x; *max=y; } else{ *min=y; *max=x; } void main(){ int a,b,min,max; printf("Enter a and b\n"); scanf("%d%d",&a,&b); minmax(a,b,&min,&max); printf("min: %d, max: %d\n",min,max); }

19. 01234567 A int A[8]; i-th array element - A[i -1] Zero based A[3]

20.  Zeroing of the whole array: ◦ for(i=0; i<10; i++) A[i]=0;  Copying of array to another array ◦ for(i=0; i<10; i++) A[i]=B[i];  Loop required for similar array operations – comparison, print, etc.

21. 1000 2200 3330 int A[3][4] = {{1},{2,2},{3,3,3}};

22. 1000 22 -2-2 0 3330 A[1][2] = -2;

23. 100022-203330 A[0][1]A[1][2]A[2][0]

24.  Functions can accept arrays as arguments  Usually the array’s size also needs to be passed (why?)  Changes in the function affect the original array!! ◦ int main(int argc, char** argv);

25. int CalcSum(int arr[], int size) { int i; int sum = 0; for(i=0; i<size; i++) sum += arr[i]; return sum; } #include #define SIZE 10 int main() { int input[SIZE], i; printf("Please enter a list of %d integers:\n“, SIZE); for(i=0; i<SIZE; i++) scanf("%d", &input[i]); printf("The sum is %d\n", CalcSum(input, SIZE)); return 0; }

26. S is actually a pointer to S[0] int S[10]; int *P; P=S; /* From now P is equivalent to S */ Both P and S are now pointing to S[0]

27.  When an array is defined, a fixed amount of memory (the size of the array) is allocated. ◦ The array variable is set to point to the beginning of that memory segment  When a pointer is declared, it is uninitialized (like a regular variable)  Unlike pointers, the value of an array variable cannot be changed  Pointers are not necessarily arrays

28.  Pointers can be incremented and decremented  If p is a pointer to a particular type, p+1 yields the correct address of the next variable of the same type  p++, p+i, and p += i also make sense

29.  If p and q point to elements in an array, q-p yields the number of elements between p and q.

30. int nums[] = {1, 2, 3}; char str[] = “moshe”; int *q = nums; char *p = str; 123 qp moshe\0

31. int nums[] = {1, 2, 3}; char str[] = “moshe”; int *q = nums; char *p = str; 123 (q+1)(p+3) moshe\0

32. void main() { int a[6],*p,*q,i; p = &a[0]; *p = 50; q = &a[1]; *(p+2) = 7; *q=9; *(q+3)=*(p+1); i=q-p; } MemoryAddresses 0 35 5572 a: 5572 17 528 p: 528 2 10 5572 7 q: 3028 3028 6080 50 5576 9 9 i: 6080 59 7663 3 13 1

33. void my_strcpy(char *dest, char *src) { while (*src != '\0') { *dest = *src; dest++; src++; } *dest = '\0'; }

34. int i,array[10]; int *ptr; ………………….. for (i=0; i<10; i++) printf(“%d”, array[i]); for (i=0; i<10; i++) printf(“%d”, *(array+i)); for (ptr=array; ptr <= &array[9]; ptr++) printf(“%d”, *ptr); /* Using array and index */ /* Using a pointer */ /* Using array as pointer and index */

35.  Normally a function accepting an array will be declared, for example – int func(int arr[]);  We might want to declare a function accepting a 2D array with – int func2(int arr2D[][]);  This is a mistake!

36.  int func2(int arr[][4]);  A 2D array is actually an array of arrays ◦ int arr[3][4] – is an array of 3 integer arrays, each of size 4

37.  When passing a 2D array to a function, we are actually passing a usual array, where each element is an array ◦ We must pass the size of each element  Note – it’s also legal to declare int func2(int arr[3][4]); ◦ The ‘3’ is meaningless but harmless