一个表达式中包括变量、常量、操作符、圆括号，圆括号可以嵌套, 编写程序判断表达式中的括号是否正确匹配。输入任意一个表达式，判断其中括号是否匹配，匹配, 输出OK, 不匹配，输出NO。(表达式的长度小于50)-An expression, including variables, constants, operators, parentheses, parentheses can be nested, write a program to determine whether the correct expression in the parentheses matches. Enter any expression, to determine which bracket match, match, output OK, do not match, the output NO. (Expression of the length is less than 50)