function template
<algorithm>

# std::replace

```template <class ForwardIterator, class T>
void replace (ForwardIterator first, ForwardIterator last,
const T& old_value, const T& new_value);```
Replace value in range
Assigns new_value to all the elements in the range `[first,last)` that compare equal to old_value.

The function uses `operator==` to compare the individual elements to old_value.

The behavior of this function template is equivalent to:
 ``123456789`` ``````template 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; } }``````

### Parameters

first, last
Forward iterators to the initial and final positions in a sequence of elements that support being compared and assigned a value of type T. The range used is `[first,last)`, which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
old_value
Value to be replaced.
new_value
Replacement value.

none

### Example

 ``123456789101112131415161718`` ``````// replace algorithm example #include // std::cout #include // std::replace #include // std::vector int main () { int myints[] = { 10, 20, 30, 30, 20, 10, 10, 20 }; std::vector 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::iterator it=myvector.begin(); it!=myvector.end(); ++it) std::cout << ' ' << *it; std::cout << '\n'; return 0; }``````

Output:
 ```myvector contains: 10 99 30 30 99 10 10 99 ```

### Complexity

Linear in the distance between first and last: Compares each element and assigns to those matching.

### Data races

The objects in the range `[first,last)` are accessed and potentially modified.

### Exceptions

Throws if any of the element comparisons, element assignments or operations on iterators throw.
Note that invalid arguments cause undefined behavior.