程序正在跳过fgets而不允许输入 [英] Program is skipping fgets without allowing input

问题描述

基本上如标题所示..当从控制台运行我的程序时，它将询问您是否要加密或解密..当我输入e或E时，它将创建一个新的空行(直到我输入了某种文本)，然后一次显示输入文本"和输入键"两行.

Basically as the title says.. When my program is run from the console, it'll ask if you'd like to encrypt or decrypt.. and when I input e or E, it creates a new blank line (until I input some kind of text), then shows the "enter the text" and "enter the key" lines all at once..

因此，在控制台中，其外观类似于:

So, in the console it would look something like:

您想(E)ncrypt或(D)ecrypt? e

Would you like to (E)ncrypt or (D)ecrypt? e

asdf jkl; < ----随机用户输入以使程序继续.

asdf jkl; <---- random user input to get the program to continue..

输入您要加密的文本:输入用于加密的密钥:(用户输入)

Enter the text you would like to encrypt : Enter a key to use for encryption : (user input)

然后程序退出..

//message to be encrypted
char text[250]; 
//word to use as the key
char key[50];
//stores the encrypted word
char encrypted[250];

char answer;
printf("Would you like to (E)ncrypt or (D)ecrypt? ");
scanf(" %c", &answer);

if(answer == 'e' || answer == 'E')
{
    printf("Enter the text you want to encrypt : ");
    fgets(text, 250, stdin);

    printf("Enter a key to use for encryption : ");
    fgets(key, 50, stdin);

    printf("Encrypted text : ");

    //code that encrypts the text here      
}

那么问题就在于，它完全跳过了fget，而没有等待/允许用户输入任何答案.为什么?

So the problem, then, is that it's skipping the fgets entirely and not waiting/allowing the user to input any answers.. why for?

推荐答案

行scanf(" %c", &answer);将newline留在输入缓冲区中，由fgets占用. " %c"中的前导空格使用前导空格，但不使用 trailing 空格.

The line scanf(" %c", &answer); is leaving a newline in the input buffer which is taken by fgets. The leading space in " %c" consumes leading whitespace but not trailing whitespace.

使用scanf中的"%*c"格式说明符可以删除newline，该说明符读取newline但将其丢弃.无需提供var参数.

You can get rid of the newline with the "%*c" format specifier in scanf which reads the newline but discards it. No var argument needs to be supplied.

#include <stdio.h>

int main(void)
{
    char answer;
    char text[50] = {0};
    scanf(" %c%*c", &answer);
    fgets(text, sizeof text, stdin);
    printf ("%c %s\n", answer, text);
    return 0;
}

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