C++ STL std::replace() function explanation with example

C++ STL std::replace() function explanation with example:

replace is defined in algorithm header in C++. We can use this method to replace one value with a new value in a given range. In this post, we will learn how to use replace with example.

Syntax of std::replace():

Below is the syntax of std::replace():

void replace(Iterator first, Iterator last, const T& old, const T& new)

Here, first : It is the forward iterator to the initial position of the sequence last : It is the forward iterator the the last position of the sequence old : Old value to be replaced new : New value to replace with old

This method replaces the old value with new in range first and last.

Return value of std::replace():

It’s return value is void or it don’t return any value. It uses operator == to compare the new value with old value.

C++ program:

Below is the complete C++ program :

#include<algorithm>
#include<iostream>

using namespace std;

void printArray(int *arr, int size){
  for(int i = 0; i< size; i++)
    cout<<arr[i]<<" ";

  cout<<endl;
}


int main(){
  int givenArr[] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1};
  int size = sizeof(givenArr)/sizeof(givenArr[0]);

  cout<<"Given Array :"<<endl;
  printArray(givenArr, size);

  replace(givenArr, givenArr + 10, -1, 0);

  cout<<"Modified Array :"<<endl;
  printArray(givenArr, size);

  return 0;
}

Here,

We are using header. But we can also use <bits/stdc++.h> .
printArray is a function to print the contents of an array. We can pass one array and its length to this function and it will print the array.
givenArr is the given array. This array is filled with -1 at the beginning of the program.
size is the size of givenArr.
We are printing the content of the array before and after using replace. We are using replace to replace all contents in the array from starting index 0 to index 9. It replaces -1 with 0.

Output:

If you run this program, it will print the below output:

Given Array :
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
Modified Array :
0 0 0 0 0 0 0 0 0 0 -1 -1 -1 -1

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