std::replace

template <class ForwardIterator, class T>
  void replace (ForwardIterator first, ForwardIterator last,
                const T& old_value, const T& new_value)
{
  while (first!=last) {
    if (*first == old_value) *first=new_value;
    ++first;
  }
}

// replace algorithm example
#include <iostream>     // std::cout
#include <algorithm>    // std::replace
#include <vector>       // std::vector

int main () {
  int myints[] = { 10, 20, 30, 30, 20, 10, 10, 20 };
  std::vector<int> myvector (myints, myints+8);            // 10 20 30 30 20 10 10 20

  std::replace (myvector.begin(), myvector.end(), 20, 99); // 10 99 30 30 99 10 10 99

  std::cout << "myvector contains:";
  for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return 0;
}