Thread: reversing strings

Hi,
I found this code in the source section of this web site. My question is this; how could a person cout the string entered in reverse? For example, if the user enters "der" the program should output "red" ? Thanks!

Code:

#include <iostream.h>

int main()

{

  char string[256];   //A nice long string

  cout<<"Please enter a long string: ";

  cin.getline(string, 256, '\n'); //The user input goes into string

  cout<<"Your long string was:"<<endl<<string;

  return 0;

}

One way is to use recursion.

Code:

#include <iostream>

void printReverse(char* s) {
	if (*s == '\0') return;
	printReverse(s+1);
	std::cout << *s;
}

int main() {
	char buf[256];
	std::cin.getline(buf, 256, '\n');
	std::cout << buf << std::endl;
	printReverse(buf);
	std::cout << std::endl;
}

Another, perhaps easier way, would be to use a for loop that started from strlen(buf) and went down to 0, outputting the character at the index everytime... but that's not as fun to think about.

create a temporary array and put the last character in the first slot of the array and then copy that array over to the original. use 2 for loops, one which increments and one which decrements

Hey,
Thanks all! Most of the code is way above me right now; I haven't gotten that far in my learn C++ in 21 days book. However, I do recognize the for loops! Could somebody show me an example using the two for loops?

Hey Prelude or SilentStrike, what are the double colons?

Code:

#include <iostream>
#include <cstring>
using namespace std;
int main()
{
  char orig[80];
  cout << "enter a string of less than 80 char" << endl;
  cin.getline(orig, 79);
  int i;
  int length = strlen(orig);
  char copy[80];
  char temp;
  strcpy(copy, orig);
  for(i = 0; i < length/2; i++)
  {
     temp = copy[i];
     copy[i] = copy[length - 1 - i];
     copy[length - 1 - i] = temp;
  }
  cout << copy<< endl
  cout << orig << endl;
  return 0;
}

Code:

#include <iostream>
void rev(char);
int main()
{
	char str[80];
	std::cout << "Enter a string -> ";
	std::cin.getline(str, 80);
	rev(str);
	std::cout << Your string has been reversed -> " << str;
	return 0;
}
void rev(char * pstr)
{
	int len = 0;
	char * pend = pstr;
	while(*((++pend)+1) != '\0');
	len = pend - pstr;
	char cbeg,cend;
	for (int i=0;i <= len/2;i++)
	{
		cbeg = *(pstr+i);
		cend = *(pend-i);
		*(pstr+i) = cend;
		*(pend-i) = cbeg;
	}
}

Originally posted by Prelude
I may just be a bit picky Nippashish, but that is way overcomplicating things. I'm curious to know why you wrote your reverse function that way.

-Prelude

I didn't write it that way for any particular reason, I just wrote it and it that's how it turned out. I'm curious to know why you say it's so overcomplicated. (I don't doubt you, it's just I'd like to know what I'm missing).

Hi,
Ok I think I'm getting closer but something is still not right. When I run this code it should reverse the code entered. It only reverses the first 2 characters. Where am I going wrong? Thanks!

Code:

#include<iostream.h>
#include<string.h>

int main()
{
	char orig[50],copy[50];
	char temp;
	int i,length;

	cout<<"\nEnter string: "<< endl;
	cin.getline(orig,49);
	length = strlen(orig);
	strcpy(copy,orig);

	for(i=0;i<length;i++)
	{
		temp=copy[i];
		copy[i]=copy[length-1-i];
	}

	cout<<copy<<endl;
	return 0;
}

Originally posted by mcorn
Hi,
Ok I think I'm getting closer but something is still not right. When I run this code it should reverse the code entered. It only reverses the first 2 characters. Where am I going wrong? Thanks!

Code:

#include<iostream.h>
#include<string.h>

int main()
{
	char orig[50],copy[50];
	char temp;
	int i,length;

	cout<<"\nEnter string: "<< endl;
	cin.getline(orig,49);
	length = strlen(orig);
	strcpy(copy,orig);

	for(i=0;i<length;i++)
	{
		temp=copy[i];
		copy[i]=copy[length-1-i];
	}

	cout<<copy<<endl;
	return 0;
}

the loop should appear like this ......

for(i = 0; i < length/2; i++)
{
temp = copy[i];
copy[i] = copy[length - 1 - i];
copy[length - 1 - i] = temp;
}