#include <stdio.h>
#include <stdlib.h>
#include <conio.h>

void upper(char* s, char* us)
{
    while(*s != '\0')
    {
        if(*s >= 'a' && *s <= 'z')
        {
            *us = *s - 32;
        }
        else
        {
            *us = *s;
        }
        s++;
        us++;
    }
    *us
 
 = '\0';//注意不要漏了這一句
}

int main()
{
    char A[20],B[20];
    printf("Please input a string:\n");
    scanf_s("%s", A, 20);
    upper(A,B);
    printf("%s", B);
    printf("%c", A[19]);//A[19]存的是'\0'
}