how to change the element of vector

[blacksource]

how can i change the element of vector.
for example the vector is : 3,2,5,8,7
i want to change the second number 2 to 6

[cilu]

std::vector<int> arr;
arr.push_back(3);
arr.push_back(2);
arr.push_back(5);
arr.push_back(8);
arr.push_back(7);

// method 1
arr[1] = 6;

// method 2
std::vector<int>::iterator pos = arr.begin() + 1;
*pos = 6;

See this article on std::vector.

[GNiewerth]

Instead of accessing elements by its index you´d better use the replace function (in case you want to replace all occurences...):

std::vector<int> arr;
arr.push_back(3);
arr.push_back(2);
arr.push_back(5);
arr.push_back(8);
arr.push_back(7);

// replace all occurences
replace( arr.begin(), arr.end(), 2,6 );

// replace first occurence of 2
std::vector<int> pos = find( arr.begin(), arr.end(), 2 );
if( pos != arr.end() )
{
   *pos = 6;
}

Regards,
Guido

[cilu]

Instead of accessing elements by its index you´d better use the replace function (in case you want to replace all occurences...):

Don't you think that depends on the logic of the program? What if he wants to change the third occurence of 2 with 6? In that case none of your samples (which are good OTOH) can help.

[GNiewerth]

Don't you think that depends on the logic of the program? What if he wants to change the third occurence of 2 with 6? In that case none of your samples (which are good OTOH) can help.

I agree with that... but somehow you have to know which element you want to replace. I wanted to show how you can replace items regardless of their position.
However, if you want to replace an item that requires certain criterions you can use replace_if and provide a predicate that checks these criterions.

Regards,
Guido

[blacksource]

thanks

but i can`t find the problem with my code

void CDelta::Decompose( int m, int n)
{
 int index = 0;
 if( m==0 )
  CreateU( index++ ); 
 else
  for( int i = m; i >= 1; i-- )
  {
   if( n == 0 || i <= m_vectTemp[n-1] )
   {
	if( m_vectTemp.size() > n )
	 m_vectTemp[n] = i;
	else
	 m_vectTemp.push_back( i );
	Decompose( m-i, n+1 );
   }
  }
/*  
	int i; 
 if(m==0) 
  show(n); 
 else 
  for(i=m;i>=1;i--) 
   if(n==0||i<=a[n-1]) 
   {
	a[n]=i;
	decompose(m-i,n+1);
   } 
*/
}

there is no error when debugging, but it prompt error when running

[Sarevok]

What is the error that it prompts?

[blacksource]

the system show a dialog which prompt:
there is something wrong with vector.exe, it must be colsed...........
please send the report of problem to Microsoft............
( i just translated it to english )

[Sarevok]

Does the vector contain some elements when you call Decompose? Can you post the code where it calls Decompose the first time?

[blacksource]

i just inited it as vector< int > m_vectTempbut when i push some zeros in it,
the system prompted error also

the error was prompted when the first time to run to m_vectTemp[n] = i
(n == 0 )

[Sarevok]

well if n==0 then the second condition in your if statement would be m_vectTemp[0-1] which clearly is an error.

[blacksource]

if( n == 0 || i <= m_vectTemp[n-1] )
if n==0 the second condition will not be judged

[Sarevok]

IMHO the second condition is still judged.

[blacksource]

Oh my god!
the error happend not in the function of Decompose but CrateU

[Sarevok]

IMHO the second condition is still judged.

Ok I was wrong. I tried it and the second condition was not judged. My bad.