if-else语句

#include <stdio.h>
//判断输入值是否大于0
int main() 
{
    int i;
    while (scanf("%d",&i))
    {
        if (i > 0)//不要在括号后加分号
        {
            printf("i is bigger than O\n");
        }else {
            printf("i is not bigger than O\n");
            }
        }
    return O;
}

if(number>500)cost=0.15;
    else if(number>300)cost=0.10;
        else if(number>100)cost=0.075;
            else if(number>50)cost=0.05;
                else cost=0; 

练习题

1、关系表