std::replace and std::replace_if in C++

std::replace

Assigns new_value to all the elements in the range [first, last) that compare to old_value. The function use operator == to compare the individual elements to old_value 

Function Template : 

void replace (ForwardIterator first,   ForwardIterator last,  const T& old_value, const T& new_value) first, last : Forward iterators to the initial and final positions in a sequence of elements. old_value : Value to be replaced. new_value : Replacement value.

Return Value : 
This function do not return any value. If elements that needs to be replace is found then element 
replaced otherwise remain unchanged. 

Examples: 

Input : 10 20 30 30 20 10 10 20 Output : 10 99 30 30 99 10 10 99 // Replaced value 20 in vector to 99. Input : 3 5 7 8 9 5 4 Output : 3 5 7 12 9 5 4 // Replaced value 8 by 12.

// CPP program to find and replace the value // with another value in array // using std::replace #include <bits/stdc++.h> using namespace std; // Driver code int main() {  int arr[] = { 10, 20, 30, 30, 20, 10, 10, 20 };  int n = sizeof(arr) / sizeof(arr[0]);  // variable containing the old and new values  int old_val = 20, new_val = 99;  // print old array  cout << "Original Array:";  for (int i = 0; i < n; i++)  cout << ' ' << arr[i];  cout << '\n';  // Function used to replace the values  replace(arr, arr + n, old_val, new_val);  // new array after using std::replace  cout << "New Array:";  for (int i = 0; i < n; i++)  cout << ' ' << arr[i];  cout << '\n';  return 0; } 

Original Array: 10 20 30 30 20 10 10 20 New Array: 10 99 30 30 99 10 10 99

std::replace_if

Assigns new_value to all the elements in range [first, last) for which pred returns true. 
Function Template :  

void replace_if (ForwardIterator first, ForwardIterator last,  UnaryPredicate pred, const T& new_value) first, last : Forward iterators to the initial and final positions in a sequence of elelments. pred : Unary function that accepts an element in the range as argument, and returns a value convertible to bool.The returned value indicate whether the element is to be replaced (if true, it is replaced). The function shall not modify its argument. old_value : Value to be replaced. new_value : Replacement value. 

Examples: 

Input : 1 2 3 4 5 6 7 8 9 10 Output : 0 2 0 4 0 6 0 8 0 10 // Replaced all odd values to 0. Input : 10 20 30 30 20 10 10 20 Output : 10 4 30 30 4 10 10 4 // Replaced all number divisible by 4 to 4.

// CPP code to find all the elements that are odd // and replace them with 0. // using std::replace_if #include <bits/stdc++.h> using namespace std; // Function that is used in std::replace_if // If number is odd return 1, else 0 // 1 (True) means replace the number // 0 (False) means does not replace bool IsOdd(int i) {   return ((i % 2) == 1);  } // Driver code int main() {  int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };  int n = sizeof(arr) / sizeof(arr[0]);  // print old array  cout << "Original Array:";  for (int i = 0; i < n; i++)  cout << ' ' << arr[i];  cout << '\n';  // replacement value  int new_val = 0;  // replace_if function  replace_if(arr, arr + n, IsOdd, new_val);  // new array after using std::replace  cout << "New Array:";  for (int i = 0; i < n; i++)  cout << ' ' << arr[i];  cout << '\n';  return 0; } 

Original Array: 1 2 3 4 5 6 7 8 9 10 New Array: 0 2 0 4 0 6 0 8 0 10

Also you can add any kind of function in std::replace_if that can only have one argument only.