习题2-2 阶梯电价（15 分）water

#include

int main()
{
    int num;//num用来接收用电量
    double cost;

    scanf("%d",&num);

    if(num<0) printf("Invalid Value!");
    else if(num>=0&&num<=50){
        cost=0.53*num;
        printf("cost = %.2f",cost);
    }
    else{
        cost=50*0.53+(num-50)*0.58;
        printf("cost = %.2f",cost);
    }

    return 0;
 }