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Friday, February 1, 2007

Friday, February 1, 2007. Minds are like parachutes. They only function when they are open. - Sir James Dewar, Scientist (1877-1925). Please note!. TA: Mansoor Akhtar Email: mmansoor @lums.edu.pk Email is NOT mansoor@lums.edu.pk.

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Friday, February 1, 2007

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  1. Friday, February 1, 2007 Minds are like parachutes. They only function when they are open. - Sir James Dewar, Scientist (1877-1925)

  2. Please note! TA: Mansoor Akhtar Email: mmansoor@lums.edu.pk Email is NOT mansoor@lums.edu.pk

  3. char wordsb[11][80]={"Mechanics", "this", "help", "please", "is", "writing", "count", "natural", "select", "thought", "" }; int i=1; while(strcmp(wordsb[i],"")) { cout<<wordsb[i]<<" "; i+=3; }

  4. char *words2[11]={"Mechanics", "this", "help", "please", "is", "writing", "count", "natural", "select", "thought", "" }; int i=1; while(strcmp(words2[i],"")) { cout<<words2[i]<<" "; i+=3; } Memory Drawing!

  5. char *words2[11]={"Mechanics", "this", "help", "please", "is", "writing", "count", "natural", "select", "thought", "" }; int i=1; while(words2[i][0]) { cout<<words2[i]<<" "; i+=3; }

  6. char *words2[11]={"Mechanics", "this", "help", "please", "is", "writing", "count", "natural", "select", "thought", "" }; int i=1; while(*words2[i]) { cout<<words2[i]<<" "; i+=3; }

  7. char *words2[11]={"Mechanics", "this", "help", "please", "is", "writing", "count", "natural", "select", "thought", "" }; int i=1; while(*(*(words2+i)+0)) { cout<<words2[i]<<" "; i+=3; }

  8. Multiple Indirection • int **balptr2ptr; //variable that is a pointer to a pointer • balptr2ptr is a pointer to an int pointer Pointer Pointer Variable address address value

  9. Multiple Indirection int main() { int x, *p, **q; x = 10; p = &x; q = &p; cout << q <<" "<<&p<<endl; cout << *q <<" "<<p<<" "<<&x<<endl; cout << **q <<endl; return 0; }

  10. Multiple Indirection int main() { int x, *p, **q; x = 10; p = &x; q = &p; cout << q <<" "<<&p<<endl; cout << *q <<" "<<p<<" "<<&x<<endl; cout << **q <<endl; // prints the value of x return 0; }

  11. Multiple Indirection 0x0012FEC8 0x0012FEC8 0x0012FED4 0x0012FED4 0x0012FED4 10

  12. void f1(int* &num) { cout<<*num<<endl; num++; num++; cout<<*num<<endl; } int main(void){ int a[8]={1,2,3,4,5,6,7,8}; int *aptr=a; f1(aptr); cout<<*aptr<<endl; return 0;} //OUTPUT?

  13. void f1(int** num) { cout<<*(*num)<<endl; (*num)++; (*num)++; cout<<*(*num)<<endl; } int main(void){ int a[8]={1,2,3,4,5,6,7,8}; int *aptr=a; int **aptr_ptr; aptr_ptr = &aptr; f1(aptr_ptr); cout<<*aptr<<endl; return 0; } //OUTPUT?

  14. int **ppi=? //what comes here?

  15. pointers – another example char *words[11]={"Mechanics", "this", "help", "please", "is", "writing", "count", "natural", "select", "thought", "" }; char **ptr=words; ptr++; while(**ptr) { cout<<*ptr<<" "; ptr+=3; }

  16. SELF TEST: const • Variables declared with const modifier cannot have their values changed during the execution of program. const float f=56.4; • The variable can be used in expressions. • Most common use is to create const pointer parameters • A const pointer prevents the object pointed to by a pointer parameter from being modified by a function.

  17. SELF TEST: const const char*sPtr sPtr is a Pointer to a character constant

  18. SELF TEST: const void code(const char *str); int main() { code("this is a test"); cout<<endl; return 0; } void code(const char *str) { while(*str) { cout << (char) (*str+1); str++; } }

  19. SELF TEST: const // This is wrong. void code(const char *str) { while(*str) { *str = *str + 1; cout << (char) *str; str++; } } // Error ?

  20. SELF TEST: const // This is wrong. void code(const char *str) { while(*str) { *str = *str + 1; //can’t modify *str cout << (char) *str; str++; } } // Error ?

  21. SELF TEST: const // const references cannot be modified. void f(const int &i); int main() { int k = 10; f(k); return 0; } void f(const int &i) { i = 100; cout << i; } // Error ?

  22. SELF TEST: const void printCharacters(const char *); main() { char string[] = "print characters of a string"; cout << "The string is:" << endl; printCharacters(string); cout << endl; return 0; } void printCharacters(const char *sPtr) { for ( ; *sPtr != '\0'; sPtr++) // no initialization cout << *sPtr; }

  23. static Variables • Variables of type static are permanent variables within their own functions or file. • They differ from global variables because they are not known outside their function or file. static local variables • When the static modifier is applied to a local variable, they maintain their values between function calls. (That is the value is not lost when the function returns) • Local static variables are initialized only once, when program execution begins.

  24. static Variables • To declare a static variable, precede its type with the word static. e.g. static int count=450;

  25. static Variables void fs(void){ static int s=2; s++; cout<<s<<endl; } int main() { fs(); fs(); fs(); return 0; }

  26. static Variables 3 4 5

  27. static Variables int r_avg(int i); int main() { int num; do { cout << "Enter numbers (-1 to quit): "; cin >> num; cout << "Running average is: " << r_avg(num); cout << '\n'; } while(num > -1); return 0; }

  28. static Variables int r_avg(int i) { int sum=0, count=0; sum = sum + i; count++; return sum / count; }

  29. static Local Variables int r_avg(int i) { static int sum=0, count=0; /* initialization of static variables occurs only once, not each time the function is entered*/ sum = sum + i; count++; return sum / count; }

  30. static Global Variables (First File) int r_avg(int i); void reset(); int main() { int num; do { cout << "Enter numbers (-1 to quit, -2 to reset): "; cin >> num; if(num==-2) { reset(); continue; } cout << "Running average is: " << r_avg(num); cout << '\n'; } while(num != -1); return 0; }

  31. static Global Variables // ---------------------- Second File ---------------------- static int sum=0, count=0; int r_avg(int i) { sum = sum + i; count++; return sum / count; } void reset() { sum = 0; count = 0; }

  32. static Global Variables • local static variable is known only to the function or block of code in which it is declared • global static variable is known only to the file in which it resides

  33. int abs ( int n ); long int labs ( long int n ); double fabs ( double x );

  34. Function Overloading // abs() is overloaded three ways. int abs(int i); double abs(double d); long abs(long l); int main(){ int x= -234; long y= 5678; double d= -123.78; cout << abs(x) << "\n"; cout << abs(y) << "\n"; cout << abs(d) << "\n"; return 0; }

  35. Function Overloading int abs(int i) { cout << "using integer abs()\n"; if(i<0) return -i; else return i; } double abs(double d) { cout << "using double abs()\n"; if(d<0.0) return -d; else return d; } long abs(long l) { cout << "using long abs()\n"; if(l<0) return -l; else return l; }

  36. Function Overloading // Overload a function three times. void overlaodedf(int i); // integer parameter void overlaodedf(int i, int j); // two integer parameters void overlaodedf(double k); // one double parameter int main(void){ int x=34, y=56; double d=123.78; overlaodedf(x); overlaodedf(x,y); overlaodedf(d); return 0; }

  37. Function Overloading void overloadedf(int i) { cout << "i is " << i << '\n'; } void overloadedf(int i, int j) { cout << " i is " << i; cout << ", j is " << j << '\n'; } void overloadedf(double k) { cout << "k is " << k << '\n'; }

  38. Default Function Arguments void mystrcat(char *s1, char *s2, int len = 0); int main() { char str1[80] = "This is a test"; char str2[80] = "0123456789"; mystrcat(str1, str2, 5); // concatenate 5 chars cout << str1 << '\n'; strcpy(str1, "this is a test"); // reset str1 mystrcat(str1, str2); // concatenate entire string cout << str1 << '\n'; return 0; }

  39. Default Function Arguments // A custom version of strcat(). void mystrcat(char *s1, char *s2, int len) { // find end of s1 while(*s1) s1++; if(len==0) len = strlen(s2); while(*s2 && len) { *s1 = *s2; // copy chars s1++; s2++; len--; } *s1 = '\0'; // null terminate s1 }

  40. Default Function Arguments void myfunc(double num = 0.0, char ch = 'X') { . . . } myfunc(198.234, 'A'); // pass explicit values myfunc(10.1); // pass num a value, let ch default myfunc(); // let both num and ch default

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