#includeint main(){ float x,y; printf("请输入x的值"); scanf("%f",&x); if(x>-1) { printf("y=2x,y=%f\n",2*x); } else if(x==-1) { printf("y=3\n"); } else if(x<-1) { printf("y=4+x,y=%f\n",4+x); } return 0;}望采纳,,