Essential C++ Concepts: Functions, Pointers, and Dynamic Memory Management

1. Thursday, January 18, 2007 The question of whether computers can think is just like the question of whether submarines can swim.  -Edsger W. Dijkstra (1930 – 2002)

2. Self Test : String tokenizing: • Skip multiple spaces between words.

3. Function to swap two numbers.

4. void swap(int* sa, int *sb);//prototype int main() { int a=3; int b=5; cout<<a<<" "<<b<<endl; swap(&a, &b); cout<<a<<" "<<b<<endl; return 0; } void swap(int* sa, int *sb){ int temp=*sa; *sa=*sb; *sb=temp; }

5. Calling Functions There are three ways in C++ to pass arguments to a function: • Call by value • Call by reference with pointer arguments • Call by reference with reference arguments

6. Call Functions with pointers void f(int *j); int main() { int i=10; int *p; p = &i; // p now points to i f(p); cout << i; // i is now ? return 0; } void f(int *j) { *j = 100; //pointee of j is assigned 100 }

7. Call Functions with pointers void f(int *j); int main() { int i=10; f(&i); cout << i; return 0; } void f(int *j) { *j = 100; //pointee of j is assigned 100 }

8. Functions int cubeByValue(int n); // prototype main() { int number = 5; cout <<"The original value of number is " << number << endl; number = cubeByValue(number); cout << "The new value of number is " << number << endl; return 0; } int cubeByValue(int n) { return n * n * n; //cube local variable n }

9. Calling Functions with Pointers void cubeByReference(int *nPtr); // prototype main() { int number = 5; cout << "The original value of number is " << number << endl; cubeByReference(&number); cout << "The new value of number is " << number << endl; return 0; } void cubeByReference(int *nPtr) { // cube number in main *nPtr = *nPtr * *nPtr * *nPtr; }

10. WHAT IS WRONG WITH THE FOLLOWING? void swap(int *pa, int *pb);//prototype int main() { int a=3; int b=5; cout<<a<<" "<<b<<endl; swap(&a, &b); cout<<a<<" "<<b<<endl; return 0; } void swap(int *pa, int *pb){ int *temp; temp=pa; pa=pb; pb=temp; }

11. Calling Functions with Pointers void convert(char *sPtr); main() { char string[] = "characters and $32.98"; cout << "The string before conversion is: " << string << endl; convert(string); cout << "The string after conversion is: " << string << endl; return 0; } void convert(char *sPtr) { while (*sPtr != '\0') { if (*sPtr >= 'a' && *sPtr <= 'z') *sPtr = toupper(*sPtr); ++sPtr; // increment sPtr to point to the next character } }

12. Dynamic allocation The new operator int *x_ptr; x_ptr=new int; OR int *x_ptr=new int; //heap

13. Dynamic allocation int *x_ptr=new int; *x_ptr=73; int *x2_ptr=new int; *x2_ptr=65;

14. Dynamic allocation What is wrong here? int *x_ptr=new int; *x_ptr=73; int *x2_ptr; *x2_ptr=65;

15. Dynamic allocation int *x_ptr=new int; *x_ptr=73; int *x2_ptr; x2_ptr=x_ptr; *x2_ptr=65;

16. Dynamic allocation movie…

17. Dynamic allocation //What is wrong here? int *x_ptr=new int; *x_ptr=73; int *x2_ptr=new int; x2_ptr=x_ptr; *x2_ptr=65;

18. Dynamic allocation //What is wrong here? int *x_ptr=new int; *x_ptr=73; int *x2_ptr=new int; x2_ptr=x_ptr; *x2_ptr=65; //memory leak

19. Dynamic allocation int *my_ptr=new int; *my_ptr=76; cout<<*my_ptr; delete my_ptr;

20. Dynamic allocation int *my_ptr=new int; *my_ptr=76; cout<<*my_ptr; delete my_ptr; int *my_ptr=new int(76); cout<<*my_ptr; delete my_ptr;

21. Dynamic allocation Another example…

22. Dynamic allocation double *p=new double[10];/*10 element array*/ int i, size=10; for (i=0; i<size; i++){ p[i]=2.0*i; } for (i=0; i<size; i++){ cout<<p[i]<<endl; } delete []p;