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小朋友学C语言（29）：switch case语句

海天一树

发布于 2018-04-17 04:32:56

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代码可运行

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代码可运行

switch case语句与if elseif语句类似，都是从多个选择条件里选取一个来执行。

（一）先来看一个if elseif程序

#include <stdio.h>
int main() 
{
    int number;
    printf("Please input an integer between 1~7: ");
    scanf("%d", &number);
    printf("Today is ");
    if(1 == number) 
    {
        printf("Monday!");
    }
    else if(2 == number) 
    {
        printf("Tuesday!");
    }
    else if(3 == number) 
    {
        printf("Wednesday!");
    }
    else if(4 == number) 
    {
        printf("Thursday!");
    }
    else if(5 == number) 
    {
        printf("Friday!");
    }
    else if(6 == number) 
    {
        printf("Saturday!");
    }
    else if(7 == number) 
    {
        printf("Sunday!");
    }
    else
    {
        printf("a wrong day! Please input an integer between 1~7!");
    }
    return 0;
}

运行结果：

Please input an integer between 1~7: 7
Today is Sunday!

（二）再用switch case语句实现相同的功能

#include <stdio.h>
int main() 
{
    int number;
    printf("Please input an integer between 1~7: ");
    scanf("%d", &number);
    printf("Today is ");
    switch(number) 
    {
        case 1:
            {
                printf("Monday!");
                break;      
            }
        case 2:
            {
                printf("Tuesday!");
                break;      
            }
        case 3:
            {
                printf("Wednesday!");
                break;      
            }
        case 4:
            {
                printf("Thursday!");
                break;      
            }
        case 5:
            {
                printf("Friday!");
                break;      
            }
        case 6:
            {
                printf("Saturday!");
                break;      
            }
        case 7:
            {
                printf("Sunday!");
                break;      
            }
        default:
            {
                printf("a wrong day! Please input an integer between 1~7!");
                break;              
            }
    }
    return 0;
}

运行结果1：

Please input an integer between 1~7: 7
Today is Sunday!

运行结果2：

Please input an integer between 1~7: 10
Today is a wrong day! Please input an integer between 1~7!

注意： switch case的结构为

switch(表达式或变量或常量)
{
     case 条件1:
        {
            执行语句;
            break;
        }
    case 条件2:
        {
            执行语句;
            break;
        }
    ……
    default:
        {
            执行语句;
            break;
        }
}

这里“break;”表示中断，若忘了写，程序会继续执行下面的条件。

（三）试试下面这个程序

#include <stdio.h>
int main() 
{
    int number;
    printf("Please input an integer between 1~7: ");
    scanf("%d", &number);
    printf("Today is ");
    switch(number) 
    {
        case 1:
            {
                printf("Monday!");  
            }
        case 2:
            {
                printf("Tuesday!");     
            }
        case 3:
            {
                printf("Wednesday!");       
            }
        case 4:
            {
                printf("Thursday!");    
            }
        case 5:
            {
                printf("Friday!");      
            }
        case 6:
            {
                printf("Saturday!");    
            }
        case 7:
            {
                printf("Sunday!");      
            }
        default:
            {
                printf("a wrong day! Please input an integer between 1~7!");            
            }
    }
    return 0;
}

运行结果：

Please input an integer between 1~7: 3
Today is Wednesday!Thursday!Friday!Saturday!Sunday!a wrong day! Please input an integer between 1~7!

（四）用while实现多次输入

#include <stdio.h>
int main() 
{
    int number;
    printf("Please input an integer between 1~7: ");
    scanf("%d", &number);
    // 循环终止条件为number小于或等于0 
    while(number > 0)
    {               
        printf("Today is ");
        switch(number) 
        {
            case 1:
            {
                printf("Monday!");
                break;      
            }
            case 2:
            {
                printf("Tuesday!");
                break;      
            }
            case 3:
            {
                printf("Wednesday!");
                break;      
            }
            case 4:
            {
                printf("Thursday!");
                break;      
            }
            case 5:
            {
                printf("Friday!");
                break;      
            }
            case 6:
            {
                printf("Saturday!");
                break;      
            }
            case 7:
            {
                printf("Sunday!");
                break;      
            }
            default:
            {
                printf("a wrong day! ");
                break;              
            }
        }//switch
        printf("\nPlease input an integer between 1~7: ");
        scanf("%d", &number);
    }//while
    printf("Loop end!\n");
    return 0;
}

运行结果：

Please input an integer between 1~7: 7
Today is Sunday!
Please input an integer between 1~7: 5
Today is Friday!
Please input an integer between 1~7: 1
Today is Monday!
Please input an integer between 1~7: 10
Today is a wrong day!
Please input an integer between 1~7: 0
Loop end!

（五）若输入1~7，打印结果并结束程序；否则重新输入

#include <stdio.h>
void print_day(int num)
{
    switch(num) 
    {
        case 1:
        {
            printf("Monday!");
            break;      
        }
        case 2:
        {
            printf("Tuesday!");
            break;      
        }
        case 3:
        {
            printf("Wednesday!");
            break;      
        }
        case 4:
        {
            printf("Thursday!");
            break;      
        }
        case 5:
        {
            printf("Friday!");
            break;      
        }
        case 6:
        {
            printf("Saturday!");
            break;      
        }
        case 7:
        {
            printf("Sunday!");
            break;      
        }
        default:
        {
            break;              
        }
    }//switch           
}
int main() 
{
    int number;
    printf("Please input an integer between 1~7: ");
    scanf("%d", &number);
    // 默认循环条件一直为真，遇到break循环才会终止
    while(1)
    {
        if(number >= 1 && number <= 7)  
        {
            printf("Today is ");
            print_day(number);
            printf("\nProgram end!\n");
            break;
        }           
        printf("It is a wrong day!\n");
        printf("\nPlease input an integer between 1~7: ");
        scanf("%d", &number);
    }//while
    return 0;
}

运行结果：

Please input an integer between 1~7: 10
It is a wrong day!
Please input an integer between 1~7: 20
It is a wrong day!
Please input an integer between 1~7: 5
Today is a Friday!
Program end!