#include <stdio.h>
int my_tolower(int c);
int main(void)
{
int i = 0;
char str[] = "ABCD";
while( str[i] )
{
str[i] = my_tolower(str[i]);
i++;
}
puts(str);
return 0;
}
int my_tolower(int c)
{
if (c >= 'A' && c <= 'Z')
return c + 'a' - 'A';
else
return c;
}
/*
run:
abcd
*/