reversing n characters in a string

[Ajaycpp]

Hi,

I have a string like str="ABCDEFGHIJK";

need o/p like this str="CBAFEDIHGJK"

am getting "CBA" correctly after that its not printing anything.

can anyone check the following code and let me know where is the problem?

int main()
{
string str="ABCDEFGHIJK";

char str1[10],rev[10];

int n=str.length(),count=0,c=3,k=0,j=0;

for(int i=0;i<n;i++)
{
str1[i]=str[i];
count++;

cout<<str1[i]<<" and "<<count<<"and "<<c<<endl;

if(count==c)
{
cout<<"Entered into if loop"<<count<<"and"<<c<<"and "<<k<<endl;
//c=c+k;
//j=0;
cout<<c<<" and "<<k<<endl;
while(j<c)
{
rev[j]=str1[c-k-1];

cout<<rev[j]<<" and "<<str1[c-k-1]<<endl;
j++;
k++;
}

count=0;
}
/*else
{
if(count < c && str[i]=='\0')
{
for(int k=0;k<count;k++)
{
rev[k]=str1[count-1];

count--;
count=0;
}
}
}*/
}

cout<<"The string is: "<<rev<<endl;

return 0;
}

Please help me on this.

[LB]

After a google search:
http://stackoverflow.com/a/198210/1959975

[Ajaycpp]

Hi L B,

In this link, it is showing only how to reversing complete string but in my case I need reverse only no.of characters

ABCDEFGHIJK ===> CBAFEDIHGJK (Ex: no.of chars=3)

[naraku9333]

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

using namespace std;

int main() {
	string s = "ABCDEFGHIJK";
	reverse(s.begin(), s.begin()+3);
	
	cout << s << endl;
}

http://ideone.com/jP2KhI

[Ajaycpp]

HI naraku9333,

Thanks for replying but it is reversing only 1st 3 chars only after that it should be reverse DEF ==> FED and GHI==>IHG also and also should not use builtin functions.

[Cubbi]

This looks like a job for boost::offset_separator

#include <iostream>
#include <string>
#include <iterator>
#include <boost/tokenizer.hpp>

int main()
{
    std::string s = "ABCDEFGHIJK";

    int offsets[] = {3};
    boost::offset_separator f(offsets, offsets+1);
    typedef boost::token_iterator_generator<boost::offset_separator>::type Iter;

    std::string result;
    for(Iter i = boost::make_token_iterator<std::string>(s.begin(), s.end(), f); i != Iter(); ++i )
        if(i->size() == 3)
            result.append(i->rbegin(), i->rend());
        else
            result += *i;

    std::cout << result << '\n'; // CBAFEDIHGJK
}

demo: http://coliru.stacked-crooked.com/a/d92ba766844c10d2

[LB]

Ajaycpp wrote:

and also should not use builtin functions.

Where does this restriction come from? That's like saying "build a paper airplane but don't use any atoms".

[Ajaycpp]

L B@ My requirement like that only, need to reverse without using built-in functions.

[naraku9333]

#include <iostream>
#include <string>

using namespace std;

int main() {
	string s = "ABCDEFGHIJK";

	for(size_t i = 0; i + 3 < s.length(); i += 3)
	{
		s[i] ^= s[i + 2];
		s[i + 2] ^= s[i];
		s[i] ^= s[i + 2];
	}
	
	cout << s << endl;
}

http://ideone.com/jP2KhI

[Ajaycpp]

HI naraku9333,

Thanks for your reply, its working but if I took 4 its not working. I will read no. of characters at execution time.

[Zhuge]

Why don't you just edit his example so it works for a variable number?