#include<stdio.h>
void main() {
  //因为9和7都为整数，所以结果中整数1后面的小数都被截断，只保留1
  double a = 9 / 7;
  printf("a = %f\n", a);
  //若想要保留小数，则在参加运算的数字中，必须加上小数部分
  double b = 9.0 / 7;
  printf("b = %.15f\n", b);
  //9 % 7 指的是9对7取余（取模）
  int c = 9 % 7;
  printf("c = %d\n", c);
  //计算机中取模的公式为 a - a / b * b
  //-9 - (-9) / 7 * 7
  int d = -9 % 7;
  printf("d = %d\n", d);
  //9 - 9 / (-7) * (-7)
  int e = 9 % -7;
  printf("e = %d\n", e);
  //(-9) - (-9) / (-7) * (-7)
  int f = -9 % -7;
  printf("f = %d\n", f);
}

#include<stdio.h>
void main() {
  int a = 7;
  int b = a++;//等价于b = a; a = a + 1;
  printf("a = %d  b = %d\n", a, b);
  int c = ++a;//等价于a = a + 1; c = a;
  printf("a = %d  c = %d\n", a, c);
  //++a和a++可以独立使用，但两者完全等价，都是a = a + 1;
  ++a;
  printf("a = %d\n", a);
  a++;
  printf("a = %d", a);
}

#include<stdio.h>
void main() {
  //华氏温度转换摄氏温度的公式为：5 / 9 * (华氏温度 - 100),
  double Fahrenhite = 97;
  double Centigrade = 5.0 / 9 * (Fahrenhite - 100);
  printf("%f对应的摄氏温度为%f", Fahrenhite, Centigrade);
}

#include<stdio.h>
void main() {
  //double score = 97;
  //double score = 79;
  double score = 59;
  if (score >= 80) {
    printf("优秀");
  }
  else if (score >= 60 && score < 80) {
    printf("良");
  }
  else {
    printf("不合格");
  }
}

#include<stdio.h>
void main() {
  int a = 9, b = 7;
  if (b < 8 && a++ > 9) {// a++ > 9判断中先进行a > 9的判断，再进行a++
    printf("ok1\n");
  }
  printf("a = %d\n", a);
  int c = 9, d = 7;
  if (d < 8 && ++c > 9) {// ++c > 9判断中先进行c > 9的判断，再进行++c
    printf("ok2\n");
  }printf("c = %d\n", c);
  int e = 9, f = 7;
  if (f < 6 && ++e > 9) {// 如果在进行&&操作时，第一个判断的结果是false，则之后的条件就不再进行判断
    printf("ok3\n");
  }printf("e = %d", e);
}

#include<stdio.h>
void main() {
  int a = 9, b = 7;
  if (a > 7 || b++ > 7) {//在进行逻辑与时候，第一个判断的结果是true，则之后的条件不再进行判断
    printf("ok\n");
  }
  printf("b = %d\n", b);
}

#include<stdio.h>
void main() {
  //int score = 97;
  int score = 79;
  int result = score > 80;
  if (result) {
    printf("ok1\n");
  }
  if (!result) {//当result取反为真时
    printf("ok2");
  }
}

#include<stdio.h>
void main() {
  //交换a与b的值
  int a = 9;
  int b = 7;
  int temp = a;//设置一个临时变量保存a的值
  a = b;//将b赋值给a
  b = temp;//将temp赋值给b，即a原来的值复制给b，完成交换
  printf("a = %d\tb = %d", a, b);
  //+=示例
  int c = 97;
  c += a;
  printf("c = %d", c);
}