练习7-1 编写一个程序 实现大写字母转换成小写字母，小写字母转换成大写字母

#include
#include
#include


char to_lower(char c); 
int main()
{
	int c;
	while((c = getchar()) != EOF)
       	   putchar(to_lower(c));
 
	return 0;
}

char to_lower(char c) 
{
	char newchr = c;
	if(newchr >= 'a' && newchr <= 'z')
	   {
		newchr = newchr - 32;
	   }
	else if(newchr >= 'A' && newchr <= 'Z')
	  {
		newchr += 32;
	}
	
	return newchr;
}