Question

我将在我的作业中使用这一小部分代码，但是存在一些问题。当我不使用fflush(stdin)时，它不会扫描basetype。但是当我使用fflush(stdin)时，它会扫描basetype，但scanf循环内的while不会继续从缓冲区中获取字符。例如，当我输入2A时......请帮忙。

#include <stdio.h>
#include <math.h>

int main() {
    int operation, basetype, number1;
    char num1;

    printf("Please enter the number of the operation you would like to perform:");
    printf("\n1. Bitwise OR\n2. Bitwise NOT\n3. Bitwise COMPARE\n4. Exit");
    scanf("%d", &operation);
    if (operation == 1) {
        printf("You chose Bitwise OR operation.");
        printf("\nPlease enter the first number:");
        scanf(" %c", &num1);
        fflush(stdin);
        printf("\nPlease specify the base(10/16):");
        scanf("%d", &basetype);

        if (basetype == 10) {
            while (num1 != 10) {
                number1 = num1 - '0';

                if (number1 >= 1 && number1 <= 9) {
                    printf("ok");
                } else
                    printf("not ok");
                scanf("%c", &num1);
            }
        }
    }
    return 0;
}

Answer 1

@RequestMapping(value="/login",method=RequestMethod.GET) public String login(){ System.out.println("###########################"); return "login"; } @RequestMapping(value="/signup",method=RequestMethod.POST) public @ResponseBody String signup(){ System.out.println("value################33"); return "success"; }具有未定义的行为，请勿使用它来尝试刷新标准输入缓冲区。你可以写一下：

fflush(stdin);

您还应该决定是以{ int c; while ((c = getchar()) != EOF && c != '\n') continue; }还是数字来读取数字。 num1用于读取单个字符"%c"以读取十进制格式的数字。

根据您的需要量身定制"%d"格式：scanf转换用户指定基数编码的数字，8,10或16，具体取决于初始字符，就像C源代码语法一样对于整数文字。

这是一个简化的程序，可以处理使用%i前缀输入的十六进制输入，例如0x 0x40：

Answer 2

以下提议的代码：

干净地编译
包含有关代码问题的嵌入式评论
的目的是清楚地显示代码的每个部分正在做什么

Bitwise_OR

现在建议的代码：

#include <stdio.h>   // scanf(), printf(), perror()
#include <stdlib.h>  // exit(), EXIT_FAILURE
//#include<math.h>

enum
{
    Bitwise_OR = 1,
    Bitwise_NOT,
    Bitwise_COMPARE,
    Exit
};

int main( void )
{

    char operation;
    int basetype;
    int number1;
    char num1;

    puts("Please enter the number of the operation you would like to perform:");
    printf( "%s",
            "1. Bitwise OR\n"
            "2. Bitwise NOT\n"
            "3. Bitwise COMPARE\n"
            "4. Exit");
    if( 1 != scanf(" %c",&operation) )
    {
        perror( "scanf for operation failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, scanf successful

    switch( operation )
    {

        case Bitwise_OR: //<-- bitwise OR never performed
            printf("You chose Bitwise OR operation.");
            printf("\nPlease enter the first number:");
            if( 1 != scanf(" %c",&num1) )
            {
                perror( "scanf for first number failed" );
                exit( EXIT_FAILURE );
            }

            // implied else, scanf successful

            //fflush(stdin);
            printf("\nPlease specify the base(10/16):");
            if( 1 != scanf("%d", &basetype) )
            {
                perror( "scanf for base failed" );
                exit( EXIT_FAILURE );
            }

            // implied else, scanf successful

            switch(basetype)
            {
                case 10:
                    while(num1 != 10)  //<-- user entering 0x0A is extremely unlikely
                    {
                        number1=num1-'0';  //<-- what if num1 not '0'...'9'

                        if(number1>=1 && number1<=9)
                        {
                            printf("ok");
                        }

                        else
                            printf("not ok");

                        // either retry first digit or get second digit
                        scanf(" %c",&num1); //<-- leading space to consume 'white space'
                    }
                    break;

                case 16:
                    break;

                default:
                    puts( "base must be 10 or 16" );
                    break;
            } // end switch()
            break;

        case Bitwise_NOT:
            break;

        case Bitwise_COMPARE:
            break;

        case Exit:
            break;

        default:
            break;
    } // end switch()

    return 0;
} // end function: main

来自缓冲区的scanf无法正常工作

2 个答案: