Handed out: 3/11/03
This exercise uses arrays of characters, which are used to store strings of characters. A null-terminated string contains a null character ('\0') to indicate where the string ends.
For this assignment, a word is any sequence of characters that does not contain a blank, tab or newline character. For example, %quot;r92#sm" is a word. Note. You can write '\t' in a C++ program for the tab character.
Write a function that takes an array of characters holding a null-terminated string as a parameter. It should print the characters in that string backwards. For example, if given string "abcd", it should print dcba.
You should not have to tell this function how long the string is, since it can find out for itself. Function strlen computes the length (logical size, excluding the null character) of a null-terminated string. Write strlen(s) for the length of the string stored in array s. Be sure to include either system header file string.h or file cstring to use strlen.
Write a small main program that tests this function. An easy way to test it is to give it constant strings. For example, if your function is called PrintBackwards, then try writing
PrintBackwards("abcde");
to test it.
Test your function before moving on.
Write a program that starts by reading the names of two files from the user: an input file name and an output file name.
Read each file name into an array of characters. If you read an array of characters using an ifstream object such as cin, a string will be read up to a white-space character such as a blank or end-of-line. So if you write
char infilename[MAX_FILE_NAME_SIZE]; cin >> infilename;then the name of a file will be read from the user, and stored in array infilename. You will need to define constant MAX_FILE_NAME_SIZE.
Test this by having the program echo the names of the files that it read, so that you can see that they are being read correctly.
Next the program should open the input file, creating a new ifstream object, and also open the output file, creating a new ofstream object. Just use the array names as the names of the files to open. The array of characters will be treated as a string. For example, if you write
ifstream ins(infilename);then object ins is tied to the file whose name is stored in array infilename. Anything that you read from ins comes from that file. Use ins like you would cin.
Note: When you open a file, it is a good idea to check whether the file was opened successfully. You can use the fail operation for that as well. So to open a file for reading, write
ifstream ins(infilename);
if(ins.fail()) {
... what to do if filename could not be opened for reading.
}
The program should read words from the input file one at a time into another array of characters. After each word, that word should be printed backwards to the output file. Put one space between adjacent words in the output file.
You can read the word using >>, just as you did for the file name.
The program should stop when it reaches the end of the input file. You can detect the end of file by asking the ifstream object whether it has failed on the previous attempt to read. Write
if(ins.fail()) {
...
}
to ask the ins object whether it failed on the previous attempt to read.
When the program finishes, it should close both the input and the output file.
Test your program before moving on.
As written, your program puts all of the words on one line. For this step, you will maintain the line breaks that were present in the input file.
Write a function called SkipWhite. Running SkipWhite(ins) should cause white space (blanks, tabs and newline characters) to be read from file ins, until either the end of the file is reached or a nonwhite character is seen. Then SkipWhite should return the number of line-break characters ('\n') that it read.
To do this, you will need to be able to look at individual characters in the input. Use the following operations and constants.
ch = ins.peek() will put into char variable ch the next character that would be read from ins, but will not consume it from the input. If you do several peeks in a row, you will get the same character each time. If there are no more characters in the file, then ins.peek() will return the special value EOF.
ins.get() is similar to ins.peek(), but it skips over the character that it reads. If you do several get's in a row, you get successive characters of the file.
You will need to use the blank (' '), tab ('\t') and line break ('\n') characters.
Now modify your program so that, before reading each word, it uses SkipWhite to skip over white space. It should look at the result of SkipWhite, and print as many line breaks as SkipWhite skipped over before handling the next word. If there were no line breaks, then just print one space before the next word.
For example, if the file contains
T'was brillig and the slithy toves
Did gyre and gimbol in the wabe.
All mimsy were the borogoves,
And the mome raths outgrabe.
then the following would be written into the output file.
saw'T gillirb dna eht yhtils sevot
diD eryg dna lobmig ni eht .ebaw
llA ysmim erew eht ,sevogorob
dnA eht emom shtar .ebargtuo
Test your program on a file that is long enough to force a few lines of output to be printed.
Turn in a printout of your program after doing all of the steps. Be sure to follow the instructions. Implement this program step by step, as explained. Implement the exact functions that are requested. Provide a clear, complete and concise contract for each function. Write down the contract before you write the function.
Do not try to write the entire program before testing anything. This program is to be written using successive refinement, where the program is implemented gradually, and what has been implemented so far is tested at each step.