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Inverting a C-string

 
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Inverting a C-string, using pointers
ibaraku
30 Dec, 2008 - 01:42 AM
Post #1

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I am trying to invert a C string using pointers, the program inverts a string only halfway through, and leaves the other half untouched. so for example, if I enter
DreamInCode
I get
edoCnInCode

CODE

#include<iostream>
#include<string>

using namespace std;

int main() {
    string str;
    char *head, *tail, *cstr;
    int i = 0;

    cout << "Enter a string: ";
    getline(cin, str);

    cstr = new char[str.size() + 1];
    strcpy(cstr, str.c_str());

    head = &cstr[0];
    tail = &cstr[str.size() - 1];

    cout << "String inverted is: ";

    while (*head != '\0') {
        cstr[i] = *tail;
        *tail--;
        *head++;
        i++;
    }

    cout << cstr;

    cout <<"\n";

    return 0;
}



How come I can't save the inversed string into cstr???
Thanks for the help
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AmitTheInfinity
RE: Inverting A C-string
30 Dec, 2008 - 02:04 AM
Post #2

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Joined: 25 Jan, 2007
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You were just replacing starting characters with the ending ones. Try to swap them instead.

CODE

char temp;
while (head <= tail) // this should be done only halfway of string and not for complete string, as you are swapping them now.
{
        tmp = cstr[i];
        cstr[i] = *tail;
        *tail = tmp;
        *tail--;
        *head++;
        i++;
    }


I hope this will help you. smile.gif
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baavgai
RE: Inverting A C-string
30 Dec, 2008 - 04:59 AM
Post #3

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My Contributions
First, this is a bad syntax "*head++", make it "head++", far less ambiguous.

Now, you have to decide which approach to take and stick with it. Do you want to swap it in place or create another string and push it there? Or, if you don't have to store it at all or just print it?

Here's an example of the last option ( using pointers ):
cpp

char *head, *tail;

head = (char *)str.c_str();
tail = head + str.size();

cout << "String inverted is: ";
while (--tail >= head) { cout << *tail; }
cout << endl;
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