#include <math.h> #include <stdio.h> int main() { double_t a,b;//要用双精度浮点数 char ch; scanf("%lf%c%lf",&a,&ch,&b); switch (ch) { case '+': printf("%.4lf+%.4lf=%.4lf\n",a,b,a+b); break; case '-': printf("%.4lf-%.4lf=%.4lf...