#includemain(){double a,b,s; char ch; printf(":输入要计算的式子,如:10+20\n"); scanf("%lf%c%lf",&a,&ch,&b); if(ch=='+') s=a+b; else if(ch=='-') s=a-b; else if(ch=='*') s=a*b; else s=a/b; printf("(%lf)%c(%lf)=%lf\n",a,ch,b,s);}