(C++) for

Keyword enabling you to perform a for-loop.

for( [initialization] ; [condition] ; [step] )
{
  [statements]
}

This enables you to count from value X to (and not including) value Y in steps of Z:

include <iostream>


int main()
{
  const double X = 69.69;
  const double Y = 96.96;
  const double Z =  0.69;
  for (double counter=X; counter<Y; counter+=Z)
  {
    std::cout << counter << std::endl;
  }
}

Most for loops are used for working with arrays, std::vectors or other indexable classes or data types. As indexes start at 0 and cannot be negative, an indexing for loop, looks like this:

include <iostream>

include <vector>


int main()
{
  //Create a random-sized std::vector
  std::vector<int> myVector(rand()%100);
  //Fill it with random values
  const int myVectorSize = myVector.size();
  for (int i=0; i!=myVectorSize; ++i)
  {
    myVector[i] = rand()%69;
  }
  //Print it to screen
  for (int i=0; i!=myVectorSize; ++i)
  {
    std::cout << i << " : " << myVector[i] << std::endl;
    
  }
}

Prefer algorithm calls over hand-written loops [1,2].

When using STL classes like std::vector, there are techniques, using iterators and std::for_each:

include <iostream>

include <vector>


int main()
{
  //Create a random-sized std::vector
  std::vector<double> myVector(100);
  //Fill it with random values
  const int myVectorSize = myVector.size();
  for (int i=0; i!=myVectorSize; ++i)
  {
    myVector[i] = sqrt(rand()%69);
  }
  //Print it to screen
  for (std::vector<double>::const_iterator i = myVector.begin(); i!=myVector.end(); ++i)
  {
    std::cout << *i << std::endl;
  }
}

Topic links

'for' links

References

1) Bjarne Stroustrup. The C++ Programming Language (3rd edition).ISBN: 0-201-88954-4. Chapter 18.12.1: 'Prefer algorithms to loops]].
2) Scott Meyers. Effective STL. ISBN: 0-201-74962-9. Item 43: 'Prefer algorithm calls over hand-written loops'

last edited (November 6, 2006) by bilderbikkel, Number of views: 6454, Current Rev: 18 (Diff)

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