$ 6 :选择、循环

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