C语言---选择结构

#include
int main()
{
  //从键盘输入两个整数a, b, 按照从小到大顺序输出!
  int a, b;
  scanf("%d%d", &a, &b);
  if (a < b)
  {
    printf("%d<%d", a, b);
  }
  else if (a > b)
  {
    printf("%d<%d", b, a);
  }
  else
    printf("%d=%d", a, b);
  return 0;
}

#include
int main()
{
  //输入三个数a,b,c，判断由这三个数为边，能否组成一个三角形!
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);
  if (a + b > c && a + c > b && b + c > a)//算数运算符>关系运算符>逻辑运算符
  {
    printf("能组成三角形\n");
  }
  else
    printf("不能组成三角形\n");
  return 0;
}

#include
int main()
{
    int a, b, c;
    scanf("%d%d%d", &a, &b, &c);
    int temp;
    if (a > b)
    {
      temp = a;
      a = b;
      b = temp;
    }

    if (a > c)
    {
      temp = a;
      a = c;
      c = temp;
    }

    if (b > c)
    {
      temp = b;
      b = c;
      c = temp;
    }
    printf("%d  %d  %d\n", a, b, c);
}

#include
int main()
{
  char c;
  scanf("%c", &c);
  if (c >= 'a' && c <= 'z')
  {
    c -= 32;
    printf("%c\n", c);
  }
  else if (c >= 'A' && c <= 'Z')
  {
    c += 32;
    printf("%c\n", c);
  }
  else
    printf("%c\n", c);
  return 0;
}

#include

int main()
{
  int score; 
  int grade; 
  scanf("%d", &score);

  switch (score / 10)
  {
  case 10:
  case 9:
    grade = 'A';
    break;
  case 8:
    grade = 'B';
    break;
  case 7:
    grade = 'C';
    break;
  case 6:
    grade = 'D';
    break;
  default:
    grade = 'E';
    break;
  }
  printf("%c\n", grade);
}

#include
//输入一个日期(ymd), 求该日期到当年年末有多少天。
int main()
{
  int y, m, d,days=0;
  scanf("%d %d %d", &y, &m, &d);
  switch (m)
  {
      case 1:
        days += 31;
      case 2:
        days += 28;
        if ((y % 4 == 0 && y % 100 != 0) || (y % 400 == 0))
        {
          days += 1;
        }
      case 3:
        days += 31;
      case 4:
        days += 30;
      case 5:
        days += 31;
      case 6:
        days += 30;
      case 7:
        days += 31;
      case 8:
        days += 31;
      case 9:
        days += 30;
      case 10:
        days += 31;
      case 11:
        days += 30;
      case 12:
        days += 31;
      }

  days = days - d;
  printf("%d\n", days);
}

#include
#include
//输入一个形式如 “操作数 运算符 操作数”的四则运算表达式，
//输出运算的结果。(+-*/ %)
int main()
{
  double x, y, z=0;
  char c;
  scanf("%lf%c%lf", &x, &c, &y);
  switch (c)
  {
    case 37:
      z = fmod(x, y);
      break;
    case 42:
      z = x * y;
      break;
    case 43:
      z = x + y;
      break;
    case 45:
      z = x - y;
      break;
    case 47:
      z = x / y;
      break;
  }
  printf("%f\n", z);
}