Problem with recursion

[Gaijinco]

I'm trying to do a function that returns a string which is a string the
characters in inverse order of the one given as a parameter. It
compiles but it crashes! Can anyone help me?

string inverse(string s, int pos, int size)
{
if(pos==size-1)
return s;
else
{
int idx = s.size()-1;
char character = s.at(idx);
s.erase(idx);
s.insert(s.begin()+pos,character);
inverse(s,pos+1,size);
}
}

 

[Maxim Yegorushkin]

I'm trying to do a function that returns a string which is a string the
characters in inverse order of the one given as a parameter. It
compiles but it crashes! Can anyone help me?

string inverse(string s, int pos, int size)
{
if(pos==size-1)

Better:

if(pos >= size)
return s;

return s;
else
{
int idx = s.size()-1;
char character = s.at(idx);
s.erase(idx);
s.insert(s.begin()+pos,character);
inverse(s,pos+1,size);

This probably should be:

inverse(s, pos + 1, size - 2);

 

[davidrubin]

I'm trying to do a function that returns a string which is a string the
characters in inverse order of the one given as a parameter. It
compiles but it crashes! Can anyone help me?

string inverse(string s, int pos, int size)

Your implementation make far too many copies, and the contract is
unclear. If I had to guess, I'd say it returns a string which is a copy
of the characters s[pos]..s[pos+size] reversed. Is this what you mean?

 

[Gaijinco]

Yeah, if you input carlos it would output solrac but there is something
quite odd, this works fine:

void inverse(string s, int pos, int size)
{
if(pos==size-1)
{
cout << s;
return s;
}
else
{
int idx = s.size()-1;
char character = s.at(idx);
s.erase(idx);
s.insert(s.begin()+pos,character);
inverse(s,pos+1,size);
}
}

But if I try to return the string, then the program crashes. I'm not
sure why is that!

 

[Howard]

Yeah, if you input carlos it would output solrac but there is something
quite odd, this works fine:

void inverse(string s, int pos, int size)
{
if(pos==size-1)
{
cout << s;
return s;
}
else
{
int idx = s.size()-1;
char character = s.at(idx);
s.erase(idx);
s.insert(s.begin()+pos,character);
inverse(s,pos+1,size);
}
}

But if I try to return the string, then the program crashes. I'm not
sure why is that!

You defined the function as void, but then have a "return s" statement in
the first part.

If it is supposed to return a string, then define it to return a string.
And then you also need a return statement for the else condition. (Probably
"return inverse(s,pos+1,size):"? I haven't tested the thought.)

If it is not supposed to return a string, then it should be operating on s
directly, and never returning a value. In that case, make s a string&
instead, and change "return s;" to just "return;".

-Howard