/*
* Copyright 2011 Steven Gribble
*
* This file is the solution to an exercise problem posed during
* one of the UW CSE 333 lectures (333exercises).
*
* 333exercises is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* 333exercises is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with 333exercises. If not, see .
*/
// Lecture 2 exercise 1:
//
// Write a function that:
// - accepts an array of 32-bit unsigned integers, and a length
// - reverses the elements of the array in place
// - returns void (nothing)
#include // needed for the definition of NULL, printf
#include // needed for the definition of uint32_t
#include // needed for the definition of assert()
// To be painfully explicit, I'm using the C99 stdint.h header
// and the uint32_t type. I could have used "unsigned int"
// instead of uint32_t as well, but if you have some assumption
// about the # of bytes in an integer type, it's better to be
// explicit.
void ReverseArray(uint32_t *arr, unsigned int len) {
int i;
// check the obvious corner case of no reversal needed
if (len <= 1)
return;
// make sure the caller passed us a valid array
assert(arr != NULL);
// do the reversal. think through the termination
// condition carefully. If there are an even number
// of elements (2, 4, 6, ...), we want to loop through
// the first half, swapping with the second half, so
// we want (len/2) iterations. If there are an odd
// number of elements, we want to loop through
// (len-1)/2. Since we're doing integer division,
// for odd lens, (len-1/2) == (len/2). So, it's the
// same termination condition for both odd and even cases!
for (i=0; i<(len/2); i++) {
uint32_t tmp;
tmp = arr[i];
arr[i] = arr[len-i-1];
arr[len-i-1] = tmp;
}
}
// here's some code to test our function
void PrintArray(uint32_t *arr, int len) {
int i;
for (i=0; i