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Conversion of whole String to uppercase or lowercase using STL in C++

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Given a string, convert the whole string to uppercase or lowercase using STL in C++.

Examples:

For uppercase conversion
Input: s = “String”
Output: s = “STRING”

For lowercase conversion
Input: s = “String”
Output: s = “string”

Functions used : transform : Performs a transformation on given array/string. toupper(char c): Returns the upper case version of character c. If c is already in uppercase, return c itself. tolower(char c) : Returns lower case version of character c. If c is already in lowercase, return c itself.

CPP

// C++ program to convert whole string to
// uppercase or lowercase using STL.
  
#include<bits/stdc++.h>
using namespace std;
  
int main(){
    // s1 is the string which is converted to uppercase
    string s1 = "abcde";
  
    // using transform() function and ::toupper in STL
    transform(s1.begin(), s1.end(), s1.begin(), ::toupper);
    cout<<s1<<endl;
  
    // s2 is the string which is converted to lowercase
    string s2 = "WXYZ";
  
    // using transform() function and ::tolower in STL
    transform(s2.begin(), s2.end(), s2.begin(), ::tolower);
   cout<<s2<<endl;
  
    return 0;
}

                    

Output
ABCDE
wxyz

Time complexity: O(N) where N is length of string ,as to transform string to Upper/Lower we have to traverse through all letter of string once.
Auxiliary Space: O(1) 


Last Updated : 10 Jan, 2023
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