C语言基础之while的使用

一. 格式:

   1:  while (条件)

   2:   

   3:  {

   4:   

   5:  循环体

   6:   

   7:  }

   8:   

二.运行原理

1.如果一开始条件就不成立，永远不会执行循环体

2.如果条件成立，就会执行一次循环体，执行完毕，再次判断条件是否成立......

三.while常用的两个语句:break和continue

   1:  int count = 0;

   2:   

   3:  while (count<50)

   4:   

   5:  {

   6:   

   7:  ++count;

   8:   

   9:  if (count%10 != 0)

  10:   

  11:  {

  12:   

  13:  printf("做第%d次俯卧撑\n", count);

  14:   

  15:  }

  16:   

  17:  }

  18:   

1.break,直接结束整个while循环

   1:  int count=0;

   2:   

   3:  while (count < 50)

   4:   

   5:  {

   6:   

   7:  ++count;

   8:   

   9:  printf("做第%d次俯卧撑\n", count);

  10:   

  11:  if (count == 20)

  12:   

  13:  {

  14:   

  15:  break;

  16:   

  17:  }

  18:   

  19:  }

  20:   

  21:  return 0;

  22:   

  23:  }

  24:   

2.continue,结束当前的循环体，进入下一次循环体的执行

   1:  int count=0;

   2:   

   3:  while (count<50)

   4:   

   5:  {

   6:   

   7:  ++count;

   8:   

   9:  if (count%10 == 0)

  10:   

  11:  {

  12:   

  13:  // 直接结束这一次循环体，进入下一次循环

  14:   

  15:  continue;

  16:   

  17:  }

  18:   

  19:  printf("做第%d次俯卧撑\n", count);

  20:   

  21:  }

  22:   

四.while语句常见死循环

1.最简单的死循环

   1:  while(1);

2. 永无止境的”哈哈哈”

   1:  while (10)

   2:   

   3:  {

   4:   

   5:  printf("哈哈哈哈\n");

   6:   

   7:  }

   8:   

五.while应用小例子

   1:  /*

   2:  

   3:  提示用户输入一个正整数n，计算1+2+3+…+n的和

   4:  

   5:  */

   6:   

   7:  #include <stdio.h>

   8:   

   9:  int main()

  10:   

  11:  {

  12:   

  13:  // 1.提示输入

  14:   

  15:  printf("请输入一个正整数：\n");

  16:   

  17:  // 2.接收输入

  18:   

  19:  // 定义变量保存用户输入的整数

  20:   

  21:  int n;

  22:   

  23:  scanf("%d", &n);

  24:   

  25:  if (n<=0)

  26:   

  27:  {

  28:   

  29:  printf("非法输入\n");

  30:   

  31:  return 0;

  32:   

  33:  }

  34:   

  35:  // 3.计算

  36:   

  37:  // (1 + n) * n / 2;

  38:   

  39:  // 定义变量保存和

  40:   

  41:  int sum = 0;

  42:   

  43:  int number = 0; // 默认被加的数值

  44:   

  45:  while (number < n)

  46:   

  47:  {

  48:   

  49:  number++;

  50:   

  51:  sum += number; // 累加

  52:   

  53:  }

  54:   

  55:  printf("%d\n", sum);

  56:   

  57:  return 0;

  58:   

  59:  }

  60: