Exercise 10

1. Exercise 10 Review: pointers, strings and recursion

2. m o s h e 1 2 3 Pointers – reminder int nums[] = {1, 2, 3}; char str[] = “moshe”; int * q = nums; char * p = str; q p

3. m o s h e 1 2 3 Pointers – reminder int nums[] = {1, 2, 3}; char str[] = “moshe”; int * q = nums; char * p = str; (q+1) (p+3)

4. m o s h e 1 2 3 Pointers – reminder p[0] *p p[i] *(p+i) p[2] p[4] q[0] q[1] q[2] q p

5. Exercise with pointers and strings • Implement the following function: char * str_any(char *str1, char *str2); • Input – two strings str1, str2 • Output – pointer to the first instance in str1 of any of the characters contained in str2 • Write a program that accepts a string from the user and replaces all punctuation signs (,.;:!?) with spaces

6. Solution • str_any.c

7. Command line arguments • Command line arguments are arguments for the main function • Recall that main is basically a function • It can receive arguments like other functions • The ‘calling function’ in this case is the operating system, or another program

8. ‘main’ prototype int main(int argc, char * argv[]) • When we want main to accept command line arguments, we must define it like this • argc holds the number of arguments that were entered by the caller • argv is an array of pointers to char – an array of strings – holding the text values of the arguments • The first argument is always the program’s name

9. ‘main’ prototype int main(int argc, char * argv[]) 3 argc : argv : p r o g n a m e m o s h e 1 7 8

10. Example /* This program displays its command-line arguments */ #include <stdio.h> int main(int argc, char *argv[]) { int i; printf("The program's command line arguments are: \n"); for (i=0; i<argc; i++) printf("%s\n", argv[i]); return 0; }

11. Specifying the arguments • We can specify to the Visual Studio compiler what command line arguments we want to pass to our program • Project  Settings  Debug, in the ‘program arguments’ field • We can also specify the arguments directly, by using the Windows console (StartRun…, then type ‘cmd’ and drag the executable into the window. Then type the arguments and Enter)

12. Helper functions – atoi/atof int atoi(char s[]); double atof(char s[]); • Command line arguments are received in the form of strings • These functions are used when we want to transform them into numbers • For example – atof(“13.5”) returns the number 13.5. • Must #include <stdlib.h>

13. Exercise • Write a program that accepts two numbers as command line arguments, representing a rectangle’s height and width (as floating-point numbers). • The program should display the rectangle’s area and perimeter

14. Solution • args_rectangle.c

15. Recursion – reminder • Recursion: any function that calls itself • recursion base: function does something, but does not call itself • recursion rule: function does something and calls itself with a different input • Recursion can always be replaced by some loop

16. Exercise • What does this function do? What does it assume about its input string? #include <string.h> int secret(char *str) { int val, len; if (str[0]=='\0') return 0; len = strlen(str); val = str[len - 1] – '0'; str[len - 1] = '\0'; return val + secret(str)*10; }

17. Recursive palindrome • Palindrome is a string that reads the same from left to right and from right to left (ignoring case, spaces, commas and anything else that is not a letter) • Write a recursive function that decides whether a string is palindrome. Madam, I’m Adam

18. Solution • rec_palindrome.c