Upper String Without using function

upper_string.cpp

#include <bits/stdc++.h>
using namespace std;
char* mystrupr(char *s);
int main()
{
    char str[20];
    puts("Enter a string");
    cin>>str;
    mystrupr(str);
    cout<<"Upper case is : >> "<<str;
}
char *mystrupr(char* s)
{
    int i=0;
    while(s[i]!='\0')
    {
        if(s[i]>=97 && s[i]<=122)
            s[i]=s[i]-32;
        i++;
    }
    return s;
}