Multithreading in boost c++

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C++

Visual-Studio

VS2010

Boost

Hi,I am new to boost threads and i have a char type for loop.Inside my for loop i am calling a function which does different operations based on the input char....below is my code

char * letters = "ABCDEFGHIJKLMNOPQRSTUVWXZ";

  for (char * ptr = letters; *ptr != 0; ++ptr)
  {
    char ch = *ptr;
    str<< ch;
    ScaleData(str,Vector_node_double,ArrayIndex);
    ArrayIndex++;
    str.str("");
    str.clear();

  }

Inside ScaleData() function i compute some values and store them into an array..size of the array is 26 (it depends on the iterations of the for loop)..After finishing the for loop i got the biggest value from the array..My question is i want to to run for loop in different threads at the same time and store each computed value in the array..

ex :

ScaleData(A,Vector_node_double,ArrayIndex); // thread one
ScaleData(B,Vector_node_double,ArrayIndex); // thread two
ScaleData(C,Vector_node_double,ArrayIndex); // thread three
ScaleData(D,Vector_node_double,ArrayIndex); // thread four
.
.
.

Need help guys... :-)