backward string

Question

karen_CSE 0 Light Poster

21 Years Ago

Hi, I'm trying to write a program that accepts a string (a line, sentence, or phrase) and then the program has to display the contents of that string backward. for example, if I entered "starting out" the program has to convert it to "tuo gnitrats".

This is my code. But I don't know what's wrong with it.

//project #2  backward String (follow page 515,  519)
//write a function that accepts a pointer to a C-string as an argument and displays its contents backwards.

# include <iostream.h>

//function Prototype
void Backward (char *);

void main (void)
{
	char line[201];

	cout << "This program will display the contents of the entered phrase backward.\n";

cout << "Please enter a phrase of no more than 200 characters, followed by a period.\n";
cin.getline(line, 201);

	cout << "The entered string displayed backward: \n";
	cout << Backward (line) << endl;
}

void Backward (char *sentencePtr)
{
	char  *sentencePtr = set;

while (*sentencePtr != '\0' && *sentencePrt > set)
	{
		sentencePtr--;
		cout << *sentencePtr << endl; //or return sentencePtr;
	}
}

can anyone help please?

c++

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Latest Post 21 Years Ago Latest Post by karen_CSE

Dani AI

Generated 10 Months Ago

Several small issues in the original thread explain the behaviour seen: a local pointer was redeclared and an undefined name was used (so the function never saw the real buffer), the function was declared void but then streamed as if it returned a value, and input was read with the extraction operator which stops at the first space. was correct to suggest walking to the end of the string and stepping backwards; and were right that a void function cannot be used inside cout.

A simple, modern, safe solution uses std::string and std::reverse. It reads the full line (including spaces) and reverses it in place:

#include <iostream>
#include <string>
#include <algorithm>

int main() {
    std::string line;
    std::getline(std::cin, line);     // read entire line including spaces
    std::reverse(line.begin(), line.end());
    std::cout << line << '\n';
    return 0;
}

Notes and cautions: prefer int main() (return 0) over void main(). If the assignment requires C-style strings, either use std::strlen to find the terminator then output characters in reverse (watch for empty strings) or make the function return a std::string instead of being void. Avoid fixed-size buffers when possible; std::string prevents common off-by-one and overflow mistakes.

All 9 Replies

Drowzee 3 Posting Whiz in Training

21 Years Ago

I don't think you should pass sentence pointer in and then declare it again. Try taking off the 'char' in your backwards function. Also, where the heck is 'set' declared? What is it?

Narue 5,707 Bad Cop

21 Years Ago

># include <iostream.h>
#include <iostream>
using namespace std;

>void main (void)
int main()

>char *sentencePtr = set;
What is set? Why are you redeclaring sentencePtr?

>sentencePtr--;
Yea, that'll work. NOT!

Try walking to the end of the string, then back:

char *p = sentencePtr;

while ( *p != '\0' )
  ++p;

while ( p != sentencePtr )
  cout.put ( *--p );

Drowzee 3 Posting Whiz in Training

21 Years Ago

I think you got the declaration backwards for set. It makes more sense the other way around.

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karen_CSE 0 Light Poster · Answer 1 · 2005-07-26T03:30:18+00:00

Ok
I don't know why I used "set." I'm looking at the examples in my book and just kinda finding my way around. It's trial and error for me, guys. I guess I was trying to give the array a name so that the computer knows how many characters it has and works backward from there...ignore this. I don't know what I was doing.
anyway,
from the suggestions, I recode it:

//project #2  backward String (follow page 515,  519)
//write a function that accepts a pointer to a C-string as an argument and displays its contents backwards.

#include <iostream>
using namespace std;

//function Prototype
void Backward (char *);

int main ()
{
	char line[201];

	cout << "This program will display the contents of the entered phrase backward.\n";

	cout << "Please enter a phrase of no more than 200 characters, followed by a period.\n";
	cin >> line;

	cout << "The entered string displayed backward: \n";
	cout << Backward(line) << endl;
}

void Backward (char *sentencePtr)
{
	
	char *p = sentencePtr;

	while ( *p != '\0' )
	 ++p;

	while ( p != sentencePtr )
	 cout.put ( *--p );
}

and I got the following error:
X:\dtran5.pds\Chapter 10 HWa\Project #2 backward string.cpp(20) : error C2679: binary '<<' : no operator defined which takes a right-hand operand of type 'void' (or there is no acceptable conversion)

So what's wrong now?

Drowzee 3 Posting Whiz in Training · Answer 2 · 2005-07-26T03:42:20+00:00

You're calling backward out of context.
It doesn't return anything (It's void backward(char*)), so you can't get anything out of it. What you need to do is just print out the modified array.

Be careful, the way Narue's written it, it will automatically output the letters, so you can't just leave in your original cout.

Just call backward(line) after you say "The line printed backwards:"

zyruz 0 Junior Poster in Training · Answer 3 · 2005-07-26T03:45:16+00:00

Dont try to print out a void function.
change

cout << Backward(line) << endl;

to

Backward(line);
cout << endl;

karen_CSE 0 Light Poster · Answer 4 · 2005-07-26T04:01:56+00:00

Ok, I fixed that. And the problem right now is that the program only shows invert the first word of the sentence and disregards the rest of the sentence.

//project #2  backward String (follow page 515,  519)
//write a function that accepts a pointer to a C-string as an argument and displays its contents backwards.

#include <iostream>
using namespace std;

//function Prototype
void Backward (char *);

int main ()
{
	char line[201];

	cout << "This program will display the contents of the entered phrase backward.\n";

	cout << "Please enter a phrase of no more than 200 characters, followed by a period.\n";
	cin >> line;

	cout << "The entered string displayed backward: \n";
	Backward(line);
	cout << endl;
}

void Backward (char *sentencePtr)
{
	
	char *p = sentencePtr;

	while ( *p != '\0' )
	 ++p;

	while ( p != sentencePtr )
	 cout.put ( *--p );
}

How do I fix that?

Narue 5,707 Bad Cop Team Colleague · Answer 5 · 2005-07-26T04:06:57+00:00

>cin >> line;
You had it right the first time, when you were using getline. cin's >> operator stops reading at whitespace, so line only contains the first word.

karen_CSE 0 Light Poster · Answer 6 · 2005-07-26T04:12:31+00:00

dang, I'm so stupid, it's not even funny. *LOL* I'm laughing at myself right now.

guess you DO learn something new everyday.

thanks guys,

karen

backward string

Dani AI

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