输入表达式字符串，以“=”表示结束， 计算并输出表达式值。 操作数可以是整数或实数，操作符有 “+”、“-”、“*”、“/”、“^”（乘方）和 “sin( )”（正弦）、“cos( )”（余弦）、“log( )”（对数）、“ln( )”（自然对数）等函数。-Enter the expression string to " ="　indicates the end of the calculation and the output value of the expression. Operand can be an integer or a real number, the operator has " +" , " -" , " *" , " /" , " ^"　(power) and " sin ()"　(sine), " cos ()"　( cosine), " log ()"　(logarithmic), " ln ()"　(natural logarithm) and other functions.