Reverse the string..

[rajujrk]

Reverse the string
1) Use only one character variable
2) Don't Use array
3) Only one variable is allowed

Pl.. any one help ...

[questionit]

With a character variable , it is not possible to work with a string since the character variable can be assigned only single chracter.

You should use 'string' type or an array to do this.

[JosAH]

I wonder what sick mind comes up with these silly "do this and that, don't use
so and so and only use blablabla" kind of riddles all the time. I don't like these
imperatives in the text either; it must be homework.

kind regards,

Jos

[Savage]

Perhaps a structure can help,or maybe pointer to a char(Hey,it's not literally an array).I've thougth something like this might help:

typedef struct _string
{
   char _0;
   char _1;
   char _2;
   char _3:
   .
   .
   .
  //Is there a size limit?
  char _20;

}Tstring;

It is one variable,but of type Tstring.

[newb16]

If you are not allowed even to use index variable or second pointer, I think it's impossible.

If you can modify original pointer during execution, like
reverse(char*s) {
char c;
....

, it's possible but takes o(n*n) ops, like the following: take first character, mark this position in string with zero, roll to end of string ( while (*s++){} ), exchange it with last-before-zero character, roll to the start of the string ( where zero is now), exchange, etc, until you encounter zero on the first step back.

[gulyan]

do you mean you have a string, something like:

char str[] = "just a string";

and you need to revers it with only one variable?
if so you might try something like this:

Code removed per Posting Guidelines

this way the only variable you use is "i" fot the indexing.
this is a little absurd ... you have to calculate the length of str 5 times for every character. it would be simpler to have

n=strlen(str);

on the begining and use n in the rest of the code.

[weaknessforcats]

You use recursion.

On the call, put the character into the char. I the char is not 0, then, add 1 to the address of the char by coding &thechar+1. Use this as the arguiment on the recursive call.

On a call, when char is 0, your string is in the call stack.

Now return the char.

Your string will be returned in reverse order.

[JosAH]

You use recursion.

On the call, put the character into the char. I the char is not 0, then, add 1 to the address of the char by coding &thechar+1. Use this as the arguiment on the recursive call.

On a call, when char is 0, your string is in the call stack.

Now return the char.

Your string will be returned in reverse order.

Can you show us the actual code because I don't understand your explanation.
Of course I can put the reversed string somewhere else, e.g. on an output stream:

[code=c]
Code removed[/code]

... but how to put the chars back in to the memory pointed to by the initial value
of char* p?

kind regards,

Jos

[weaknessforcats]

Code removed

You really don't need to know where the string starts or ends. When you reach the end of the recursion at the last character, just push it into a stream.

Then in main(), just extract the stream into the original string.

The recursion uses only a char* and a stringstream& neither of which is a char or an array so it probably meets the problem requirement. You don't actually need a char variable.

[JosAH]

You really don't need to know where the string starts or ends. When you reach the end of the recursion at the last character, just push it into a stream.

Then in main(), just extract the stream into the original string.

The recursion uses only a char* and a stringstream& neither of which is a char or an array so it probably meets the problem requirement. You don't actually need a char variable.

Yup, that I understand but I understood differently from your previous post, i.e.
using no additional memory proportional to the size of the string, reverse it using
no other variables (except one according to the OP's rules). I considered it just
a little academic exercise ;-)

kind regards,

Jos

[whodgson]

There is a standard C++ generic algorithm 'reverse()'
if char * s="ABCDE"
reverse(s,s+5)
cout<<s<<endl;//will print EDCBA

[JosAH]

There is a standard C++ generic algorithm 'reverse()'
if char * s="ABCDE"
reverse(s,s+5)
cout<<s<<endl;//will print EDCBA

You can't write to a string constant; it induces indefined behaviour so anything
can happen according to the Standard.

kind regards,

Jos

[whodgson]

Quote:

You can't write to a string constant; it induces indefined behaviour so anything
can happen according to the Standard.

Could you amplify on the above as I am trying to learn Cpp.

[JosAH]

This is what the C99 Standard says about it:

[#5] In translation phase 7, a byte or code of value zero is
appended to each multibyte character sequence that results
from a string literal or literals.56) The multibyte
character sequence is then used to initialize an array of
static storage duration and length just sufficient to
contain the sequence. For character string literals, the
array elements have type char, and are initialized with the
individual bytes of the multibyte character sequence; for
wide string literals, the array elements have type wchar_t,
and are initialized with the sequence of wide characters
corresponding to the multibyte character sequence, as
defined by the mbstowcs function with an implementation-
defined current locale. The value of a string literal
containing a multibyte character or escape sequence not
represented in the execution character set is
implementation-defined.

[#6] It is unspecified whether these arrays are distinct
provided their elements have the appropriate values. If the
program attempts to modify such an array, the behavior is
undefined.

Pay special attention to the last paragraph.

kind regards,

Jos

[SpecialKay]

I just have to say, the thread rules <content removed>. how is anyone suspost to learn when everything is removed?