In this shot, we will discuss how to use the `replace()` function in C++.

The **`replace()`** function  replaces each element in the range [first, last) that is equal to `oldValue` with `newValue`. The function uses operator `==` to compare each of the elements to `oldValue`.
 
# 
## Parameters
* `First`: Forward iterator for the initial position of the derived range.
* `Last`:  Forward iterator for the final position of the derived range.
* `OldValue`: Replaced value.
* `NewValue`: Replacement value.

## Return value
The `replace()` function does not return anything.

## Syntax
The syntax of the `replace()` function is shown below:
```
void replace(first, last, oldvalue, newvalue);
```

## Code
Let's look at the code snippet below.






#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    vector<int> vec = {3, 1, 2, 1, 2, 1, 5, 6, 12, 5};  
    cout<<"The vector before calling replace(): ";
    for(int x: vec)
        cout << x << " ";
    
    cout << endl;
    replace(vec.begin(), vec.end(), 1, 100);
    cout<<"The vector after calling replace(): ";
    for(int x: vec)
        cout << x << " ";
    return 0;  
}



## Explanation

* *In lines 1 to 3,* we imported the required header files.
* *In line 6,* we made the `main` function.
* *In line 8,* we initialized a vector containing some integer values.
* *In lines 10 and 11*, we printed the elements of the original vector.
* *In line 14,* we used the `replace()` function to replace  `1` in the vector with the value `100`.
* *In lines 16 and 17,* we printed the vector after replacement.

In this way, we can use the `replace()` function to replace the elements present inside containers in C++.


How to use the replace() function in C++

Replace elements in a container using C++'s replace() function by specifying range and values.