Practice Assignment

(reversewords.c)

Information

Before writing any code, you should write down the steps (in English or your native language) you need to take to solve these problems. This is your pseudocode. Once you have your pseudocode written, you can convert it into C code. If you can't write down the steps in English, you certainly can't write it in C.

Both of the functions you'll be writing deal with NUL-terminated C-style strings. The only header file you can include is string.h, and you'll only need the strlen function.

The first function will reverse the words in a string. For example:
```
Four score and seven years ago
```
becomes
```
ago years seven and score Four
```
Notice that you are not reversing the characters in the words, just the words. The function prototype is:
```
void reverse_words1(const char input[], char output[]);
```
The input is a valid NUL-terminated C-style string and the output is the same size as the input, so you will have enough room for all of the characters including the NULL terminator.
Hint: Walk the input string backwards looking for a space character. Then copy each character of the word to its right into the output. Do this until you get to the beginning of the string and copy the first word as the last word of the output.
If you need a hint, here are some diagrams to help get you started.
Approximate number of lines of code: 25.
The second function is very similar to the first function except that you will reverse the words in place. This means there is no extra memory required. The prototype looks like this:
```
void reverse_words2(char input[]);
```
There's a clever trick that will make this easier than the first reverse function. First, reverse the entire string character-by-character:
```
This is a string
```
becomes
```
gnirts a si sihT
```
This is pretty trivial to do. You'll notice that all of the words are in their proper position. They're just reversed. Now, simply reverse the letters of each word. To make this simpler, you should create a helper function that reverses all of the characters between two pointers:
```
/* Helper function to reverse a range a characters */
void reverse(char *start, char *end)
{
  /* Reverse the characters from start to end */
}
```
You can even use this function to reverse the entire string at the start.
Approximate number of lines of code: 15.

Both of the functions go in a C file named reversewords.c. The command line to build the program is:

gcc -O -Werror -Wall -Wextra -ansi -pedantic main.c reversewords.c -o reverse

This is a partial reversewords.c with functions to get you started.

#include <string.h>

void reverse_words1(const char input[], char output[])
{

}

void reverse_words2(char string[])
{

}

Here is main.c: HTML Text

Notice the use of the #if 0 ... #endif in the file. This is a simple way to enable/disable a bunch of code in the file. You shouldn't try to pass every test at once. Work on the first test, which is very simple. When you get that test working, move the #if 0 around the next one and see if you pass that test. Continue in this way until you pass all of the tests. All the header files that you need are already included.

Output for the sample tests