Programming Forums > Application Development > C++

DaWei · Mar 18th, 2006, 11:36 AM

Well, he tried tags, but he put the opening tag BELOW the code and has no closing tag.
Put [/code] BELOW your code and [ code ] (no spaces before and after the word) ABOVE your code, woiks like this:

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This chere is code
   with some indentations
   {
      and other blocked up stuff
   }
See?

Jessehk · Mar 18th, 2006, 12:00 PM

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#include <iostream>
#include <cstdlib>

using namespace std;

int main()
{
	int i,j;
	cout << "enter the array";
	char arr[10], rr1[10];

	for(i = 0; i < 10; i++)
		cin >> arr[i];
	
	for(i = 9; i >= 0; i--)
		for(j = 0; j <= 9; j++)
			rr1[j] = arr[i];

	for(j = 0; j <= 9; j++)
		cout << rr1[j];

	system("pause");
	
	return 0;
}

The problem with your code are the nested for-loops.

Instead of taking the last element of the source array and placing it as the first element of the new array, your iterating over an array for every iteration of an array.

Try this instead:

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#include <iostream>
#include <cstdlib>

using namespace std;

int main()
{
	int i,j;
	cout << "enter an array of 10 elements:\n";
	int arr[10], rr1[10];

	for(i = 0; i < 10; i++)
	{
		cout << i + 1 << ": ";
		cin >> arr[i];
		cin.ignore();
	}
	
	for(i = 0, j = 9; i < 10; i++, j--)
		rr1[i] = arr[j];
	
	for(int x = 0; x < 10; x++)
		cout << rr1[x] << endl;

	cin.get();
	
	return 0;
}

Notice I changed the type to int instead of char. That way, you will be able to input a number rather then a single character.

DaWei · Mar 18th, 2006, 12:10 PM

There are any number of ways to reverse the elements of an array or string. If you're not interested in preserving the original (if you are, you can copy it, of course), you can put a pointer at the end and another at the beginning. Exchange the two values. Increment the beginning pointer and decrement the ending pointer. When the pointers cross, you're done. Another way is shown here. Note that I have used strings and not char arrays. You're using C++, you may as well write C++ instead of writing what is essentially C and compiling it with a C++ compiler. Strings are much easier to use, more intuitive, and the code is more robust with less effort.

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#include <iostream>
#include <string>

using namespace std;

int uhOh (string TroubleInRiverCity)
{
    cerr << TroubleInRiverCity << endl;
    return 1;
}
int main (int argc, char *argv [])
{
    string theString;
    string theReverse;

    cout << "Enter a line of text to reverse: ";
    getline (cin, theString, '\n');
    if (!cin.good ()) return uhOh ("Input failed");
    size_t length = theString.size ();
    theReverse = theString; // To set the appropriate length
    for (size_t i = 0; i < length; i++)
        theReverse [length-i-1] = theString [i];

    cout << theString << " => " << theReverse << endl;
    cout << "Press ENTER to exit the program";
    cin.sync ();
    cin.get ();
    return 0;
}

Quote:

Originally Posted by Output

Enter a line of text to reverse: This is the text
This is the text => txet eht si sihT
Press ENTER to exit the program

Jessehk · Mar 18th, 2006, 12:14 PM

Ah! I thought he wanted to reverse an array! That would explain it. *slaps head*

DaWei · Mar 18th, 2006, 2:16 PM

One could reverse an array the same way: use a vector.

DaWei · Mar 18th, 2006, 3:00 PM

Example:

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    vector <int> theThangy;
    vector <int> theReverse;
    int holdingVar;

    cout << "Enter a few integers to reverse.  Terminate with ctrl-Z on a new line." << endl;
    cout << "Go: ";
    while (1)
    {
        cin >> holdingVar;
        if (!cin.good ()) break;
        theThangy.push_back (holdingVar);
    }
    if (!cin.eof ()) return uhOh ("Input failed");
    size_t length = theThangy.size ();
    for (int i = length-1; i >= 0; i--) 
        theReverse.push_back (theThangy [i]);

    cout << "The Thangy: ";
    for (size_t i = 0; i < length; i++)
        cout << theThangy [i] << " ";
    cout << endl;

    cout << "The Reverse: ";
    for (size_t i = 0; i < length; i++)
        cout << theReverse [i] << " ";
    cout << endl;

    return 0;

Quote:

Originally Posted by Output

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\David>cd desktop

C:\Documents and Settings\David\Desktop>student
Enter a few integers to reverse. Terminate with ctrl-Z on a new line.
Go: 1 10 25 40
^Z
The Thangy: 1 10 25 40
The Reverse: 40 25 10 1

C:\Documents and Settings\David\Desktop>student
Enter a few integers to reverse. Terminate with ctrl-Z on a new line.
Go: 1 4 a georgie
Input failed

C:\Documents and Settings\David\Desktop>

Cache · Mar 18th, 2006, 4:36 PM

Quote:

Originally Posted by DaWei

Example:

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    size_t length = theThangy.size ();
    for (int i = length-1; i >= 0; i--) 
        theReverse.push_back (theThangy [i]);

Could also be done with the vector constructor:

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std::vector<std::string> theReverse( theThangy.rbegin(), theThangy.rend() );

And here is a pretty neat way to output the contents of a vector if anyone is interested (requires '#include <iterator>'):

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copy( theReverse.begin(), theReverse.end(), std::ostream_iterator<std::string>(std::cout) );

biohazard · Mar 19th, 2006, 7:27 AM

thanks da wei. the code was great.

Bench · Mar 19th, 2006, 4:50 PM

Why not use the standard library algorithm provided for this purpose?

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#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int main()
{
    string s("tnorf-ot-kcab");
    reverse(s.begin(), s.end());
    cout << s;
    cin.get();
}

DaWei · Mar 19th, 2006, 6:04 PM

Think of it this way: is he learning to use utilities and tools, or learning to code? 'reverse' didn't grow in the cottonpatch, someone wrote it. The answer to your question lies in the answer to that question.

Mar 18th, 2006, 11:36 AM	#11
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Well, he tried tags, but he put the opening tag BELOW the code and has no closing tag. Put [/code] BELOW your code and [ code ] (no spaces before and after the word) ABOVE your code, woiks like this: (Toggle Plain Text) This chere is code with some indentations { and other blocked up stuff } See? This chere is code with some indentations { and other blocked up stuff } See? __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Mar 18th, 2006, 12:00 PM	#12
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 644 Rep Power: 4	(Toggle Plain Text) #include <iostream> #include <cstdlib> using namespace std; int main() { int i,j; cout << "enter the array"; char arr[10], rr1[10]; for(i = 0; i < 10; i++) cin >> arr[i]; for(i = 9; i >= 0; i--) for(j = 0; j <= 9; j++) rr1[j] = arr[i]; for(j = 0; j <= 9; j++) cout << rr1[j]; system("pause"); return 0; } #include <iostream> #include <cstdlib> using namespace std; int main() { int i,j; cout << "enter the array"; char arr[10], rr1[10]; for(i = 0; i < 10; i++) cin >> arr[i]; for(i = 9; i >= 0; i--) for(j = 0; j <= 9; j++) rr1[j] = arr[i]; for(j = 0; j <= 9; j++) cout << rr1[j]; system("pause"); return 0; } The problem with your code are the nested for-loops. Instead of taking the last element of the source array and placing it as the first element of the new array, your iterating over an array for every iteration of an array. Try this instead: (Toggle Plain Text) #include <iostream> #include <cstdlib> using namespace std; int main() { int i,j; cout << "enter an array of 10 elements:\n"; int arr[10], rr1[10]; for(i = 0; i < 10; i++) { cout << i + 1 << ": "; cin >> arr[i]; cin.ignore(); } for(i = 0, j = 9; i < 10; i++, j--) rr1[i] = arr[j]; for(int x = 0; x < 10; x++) cout << rr1[x] << endl; cin.get(); return 0; } #include <iostream> #include <cstdlib> using namespace std; int main() { int i,j; cout << "enter an array of 10 elements:\n"; int arr[10], rr1[10]; for(i = 0; i < 10; i++) { cout << i + 1 << ": "; cin >> arr[i]; cin.ignore(); } for(i = 0, j = 9; i < 10; i++, j--) rr1[i] = arr[j]; for(int x = 0; x < 10; x++) cout << rr1[x] << endl; cin.get(); return 0; } Notice I changed the type to int instead of char. That way, you will be able to input a number rather then a single character. __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Mar 18th, 2006, 12:14 PM	#14
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 644 Rep Power: 4	Ah! I thought he wanted to reverse an array! That would explain it. slaps head __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Mar 18th, 2006, 2:16 PM	#15
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	One could reverse an array the same way: use a vector. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Mar 19th, 2006, 4:50 PM	#19
Bench Newbie Join Date: Feb 2006 Posts: 20 Rep Power: 0	Why not use the standard library algorithm provided for this purpose? (Toggle Plain Text) #include <iostream> #include <string> #include <algorithm> using namespace std; int main() { string s("tnorf-ot-kcab"); reverse(s.begin(), s.end()); cout << s; cin.get(); } #include <iostream> #include <string> #include <algorithm> using namespace std; int main() { string s("tnorf-ot-kcab"); reverse(s.begin(), s.end()); cout << s; cin.get(); }

Mar 19th, 2006, 7:27 AM	#18
biohazard Newbie Join Date: Feb 2006 Posts: 18 Rep Power: 0	thanks da wei. the code was great.

Mar 19th, 2006, 6:04 PM	#20
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Think of it this way: is he learning to use utilities and tools, or learning to code? 'reverse' didn't grow in the cottonpatch, someone wrote it. The answer to your question lies in the answer to that question. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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Programming Forums > Application Development > C++

reversing a string