COP 3223H meeting -*- Outline -*-

* Friday problems with C pointers

** capturing patterns of assignments

*** initialize an array
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            FOR YOU TO DO

write a function
  extern void set_all_array(double *a, int sz,
                         double val);
that takes an array a of doubles,
an int sz, and a double val
such that all i from 0 to sz-1 are legal indexes
and val is not NaN,
and initializes each element with index 0..sz-1
to the value val.
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** Code that uses swap

*** reverse an array
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              FOR YOU TO DO

Write a function
 extern void reverse(char *s);
that takes a null-terminated string s,
and reverses it in place.
So, if the length of s is len,
then at the end
   *s is the old value of *(s+len-1)
      and vice versa
   *(s+1) is the old value of *(s+len-2)
      and vice versa
   *(s+2) is the old value of *(s+len-3)
      and vice versa
   etc.

For example:

    char str[] = {'U', 'C', 'F'};
    reverse(str);
    ok(strcmp(str,"FCU") == 0);















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...
#include <string.h>
#include "reverse.h"

// assigns: *x, *y;
// effect: *x == old(*y) and *y == old(*x);
void cswap(char *x, char *y) {
    char temp = *y;
    *y = *x;
    *x = temp;
}


// requires: s is a null-terminated string
// let int len = strlen(s);
// ensures: for all i: 0 <= i && i < len: s[i] == old(s[len-1-i]);
void reverse(char *s) {
    int len = strlen(s);
    char *front, *rear;
    for (front = s, rear = s+(len-1); front < rear; front++,rear--) {
	cswap(front, rear);
    }
}


*** insertion sort
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              FOR YOU TO DO

Write a function,

extern bool palindrome(const char *sentence)

that takes a string, sentence,
and returns true just when
sentence is a palindrome,
so that it reads the same forwards and backwards,
ignoring space and punctuation.
Note that palindrome may not change any characters in its argument.
























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