#include <iostream>
using namespace std;
 
void all_lower(char* input)
{
    if ( *input == 0 ) {
        return;
    }
 
    if ( *input >= 'A' && *input <= 'Z') {    
        *input += 32; // convert capital letter to lowercase
    }    
 
    all_lower(++input); // simply move to next char in array
}
 
int main()
{
    char test[] = "TEST";
    cout << "Before: " << test << endl;
    all_lower(test);
    cout << "After: " << test << endl;
    return 0;
}

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