char *string_toupper(char *s)
{	int i; while( s[i] != '\0' ) { // if character is in lowercase // then subtract 32 if( s[i] >= 'a' && s[i] <= 'z' ) { s[i] = s[i] - 32; } // increase iterator variable i++; } return (s); }

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

#include<iostream>
#include<string>
using namespace std;
int main()
{ string str="Hello World"; int i; cout<<"The String is: \n"<<str; cout<<endl<<endl; cout<<"String after uppercase lowercase modification: \n"; for(i=0; i < str.length(); i++) { //if its uppercase add to its Ascii code 32 to make lowercase if(str[i]>='A' && str[i]<='Z')	cout<<char(str[i]+32);	// else if its lowercase subtract 32 to make it upper case else if(str[i]>='a' && str[i]<='z')	cout<<char(str[i]-32);	// else if its a space or symbol for example just print it as is	else cout<<str[i];	//the reason this works is that the distance in Ascii from uppercase to lowercase	//is standard and constant } return 0;
}