Declaration of an array of vectors

[harsha]

When i compile this prog, i get errors sayin
1.'d' undeclared"
2.Each undeclared identifier is reported only once for each function it appears in. what is the problem here with declaration of an array of vectors??


#include<iostream>
#include<vector>
using namespace std;
int main()
{
int m,a,b,i;
cin>>m;
for(i=0;i<m;i++)
{
vector<int> d[i];
}
for(i=0;i<m;i++)
{
cin>>a>>b;
d[a].push_back(b);
}
return 0;
}

[Zhuge]

You declare d inside one of the for loops; it doesn't exist outside that for loop so an attempt to access it in the next one generates the error.

[Felicia123]

example

#include<iostream>
#include<vector>

using namespace std;

int main(){
      int SizeofLoop = 0;
      int number = 0;

      cout << "Enter looping size : ";
      cin   >> SizeofLoop;

      vector<int> v;//Vector is a container
  
      for(int i = 0 ; i < SizeofLoop ; i++ ){
            cout << "Enter number " << (i+1) << " to vector : ";
            cin   >> number;
	    v.push_back(number);
      }

	  for( int i = 0 ; i < SizeofLoop ; i++ ){
		  cout << "Number " << (i+1) << " : " << v[i] << endl;
	  }

      system( "pause" );
      return 0;
}

DO you know clearly about vector?

[harsha]

@felicia123 yeah im fine with what u've coded but my prob is wit assigning an array of vectors in a better scope

[harsha]

@zhuge yep i've got it.. but for declaring an array of vectors,, i need a loop.. so how do i define it in a better scope,, i.e how do i define it such tat it can be accessed throughout the main() function??

[Felicia123]

like that why you want to use vector?

quite confuse with yours question. haha..

[cire]

There are two problems with the original code. d only exists within the scope of the first for statement, and one may not define an array with a variable that is not also a compile-time constant: i, although some compilers have an extension enabled by default that allows it.

Since you're already using a vector, why not just use a vector of vectors?

#include <iostream>
#include <iomanip>
#include <vector>

typedef std::vector<int> int_vec ;
typedef std::vector<int_vec> vvec ;

int main()
{
    vvec v(5) ; // create a vector containing 5 vector<int>s

    unsigned count = 0 ;

    for ( unsigned i = 0; i<5 ; ++i )
        for ( unsigned j=0; j<5 ; ++j )
            v[i].push_back(count++) ;

    std::cout << "v = {\n" ;
    for ( unsigned i=0; i<v.size() ; ++i )
    {
        std::cout << "\t{ " ;
        for ( unsigned j=0; j<v[i].size(); ++j )
            std::cout << std::setw(2) << v[i][j] << ' ' ;
        std::cout << "}\n" ;
    }
    std::cout << "}\n" ;
}