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C的控制语句：循环

发布时间 2023-04-16 22:24:45作者: 俊king

C的控制语句：循环

1、三种循环方式--->for、while、do while

2、函数fabs()

3、编写有返回值的函数

三种循环方式

while

示例代码：

# include<stdio.h>
​
int main(void)
{
    long num; long sum = 0L; int status;
​
    printf("请输入一个整型整数进行求和");
    printf("(q 或者 quit 退出):");
    status = scanf("%ld", &num); // scanf()函数特性,如果scanf()函数接收到一个整数,会把该整数存入num当中,并且返回一个1赋值给status
    while (status == 1)
    {
        sum = sum + num;
        printf("请输入一个整型整数进行求和 (q 或者 quit 退出):");
        status = scanf("%ld", &num); // 如果用户输入的不是数字,scanf()函数读取失败,返回0,程序退出--->利用的scanf()的双重特性避免了循环过程中的程序交互输入问题
    }
    printf("这些整型整数的和是:%ld\n", sum);
​
    getchar();
​
    return 0;
}

变式：

# include<stdio.h>
​
int main(void)
{
    long num; long sum = 0L; int status;
​
    printf("请输入一个整型整数进行求和");
    printf("(q 或者 quit 退出):");
    while ((scanf("%ld", &num)) == 1)
    {
        sum = sum + num;
        printf("请输入一个整型整数进行求和 (q 或者 quit 退出):");
    }
​
    getchar();
​
    return 0;
}

注意：

每次循环都被称为一次迭代

循环终止条件：

# include<stdio.h>
​
int main(void)
{
    int n = 0;
​
    while (n < 7) // n < 7就是循环终止条件
    {
        printf("n = %d\n", n);
        n++;
        printf("Now n = %d\n", n);
    }
    printf("结束循环!");
​
    getchar();
​
    return 0;
}

注意：

# include<stdio.h>
​
int main(void)
{
    int n = 0;
​
    while (n < 3)
        printf("Now n = %d", n);
        n++; // 只有跟在循环条件后面的一条语句是循环语句,第二句开始就不是,所以n不会递增,while的循环条件一直为true
    printf("Down!");
​
    return 0;    
}
_Bool类型

注意：

bool 不是 c语言的关键字， 但是c99标准和c++把bool当作关键字

# include<stdio.h>
# include<stdbool.h> // 定义了Bool类型
​
int main(void)
{
    long num; long sum = 0L; _Bool input_is_good;
​
    printf("输入一个数");
    printf("q 或者 quit 退出:");
    input_is_good = (scanf("%ld", &num) == 1);
​
    while (input_is_good)
    {
        sum = sum + num;
        printf("输入一个数");
        printf("q 或者 quit 退出:");
        input_is_good = (scanf("%ld", &num) == 1);
    }
​
    printf("Down!");
​
    getchar();
​
    return 0;
}

For

/**
 * @Author: Lucifer
 * @Date: 4/16/2023, 4:40:59 PM
 * @LastEditors: Lucifer
 * @LastEditTime: 4/16/2023, 4:40:59 PM
 * Description: A case about for
 * Copyright: Copyright (©)}) 2023 Your Name. All rights reserved.
 */
# include<stdio.h>
​
int main(void)
{
    const int NUMBER = 22;
    int count;
​
    for (count = 1; count <= NUMBER; count++)
    {
        printf("Hello World!");
    }
​
    getchar();
​
    return 0;
}

字符代替数字作为测试条件和初始值:

# include<stdio.h>
​
int main(void)
{
    char ch;
​
    for (ch = 'a'; ch < 'z'; ch++) {
        printf("字符!!!");
    }
​
    getchar();
​
    return 0;
}

省略循环表达式写法:

/**
 * @Author: Lucifer
 * @Date: 4/16/2023, 5:26:45 PM
 * @LastEditors: Lucifer
 * @LastEditTime: 4/16/2023, 5:26:45 PM
 * Description: for循环当中省略表达式的写法
 * Copyright: Copyright (©)}) 2023 Your Name. All rights reserved.
 */
# include<stdio.h>
​
int main(void)
{
    int n, ans, time;
    ans = 2;
    time = 1;
​
    for (n = 3; ans <= 25;)
    {
        ans = ans * n;
        printf("循环次数: %d \n", time);
        time++;
    }
​
    printf("n = %d, ans = %d\n", n, ans * n);
​
    getchar();
​
    return 0;
}

逗号运算符运用在for循环中表达多种用法:

/**
 * @Author: Lucifer
 * @Date: 4/16/2023, 5:37:23 PM
 * @LastEditors: Lucifer
 * @LastEditTime: 4/16/2023, 5:37:23 PM
 * Description: ,运算符，在一个for循环中，每个条件表达式可以用,来表达多种条件
 * Copyright: Copyright (©)}) 2023 Your Name. All rights reserved.
 */
# include<stdio.h>

int main(void)

{

const int FIRST_OZ = 46;

const int NEXT_OZ = 20;

int ounces, cost;


printf("  ounces cost\n");
for (ounces = 1, cost = FIRST_OZ; ounces &lt;= 16; ounces++, cost += NEXT_OZ)
{
    printf("%5d    $%4.2f\n", ounces, cost / 100.0);
}

getchar();

return 0;



}

示例代码2:

/**
 * @Author: Lucifer
 * @Date: 4/16/2023, 7:41:35 PM
 * @LastEditors: Lucifer
 * @LastEditTime: 4/16/2023, 7:41:35 PM
 * Description: ZenO悖论
 * Copyright: Copyright (©)}) 2023 Your Name. All rights reserved.
 */
# include<stdio.h>

int main(void)

{

int t_ct; // 项计数

double time, power_of_2;

int limit;


printf("输入你想射几米:");
scanf("%d", &amp;limit);
// 箭永远只会行进一半的路程
for (time = 0, power_of_2 = 1, t_ct = 1; t_ct &lt;= limit; t_ct++, power_of_2 *= 2.0)
{
    time += 1.0 / power_of_2;
    printf("time = %f, 当terms = %d \n", time, t_ct);
}

getchar();
getchar();

return 0;



}

do...while

示例代码:

/**
 * @Author: Lucifer
 * @Date: 4/16/2023, 7:47:13 PM
 * @LastEditors: Lucifer
 * @LastEditTime: 4/16/2023, 7:47:13 PM
 * Description: 猜数字游戏
 * Copyright: Copyright (©)}) 2023 Your Name. All rights reserved.
 */
# include<stdio.h>

int main(void)

{

const int secret_code = 13;

int code_entered;


do
{
    printf("有一个内置的数,在10到20之间,猜猜是几?:\n");
    printf("请输入你猜的数:\n");
    scanf("%d", &amp;code_entered);
    getchar();
} while (code_entered != secret_code);

printf("猜对了,游戏结束!");

getchar();

return 0;



}