按'q'或非数字字符来退出循环/程序 [英] pressing 'q' or non-numeric char to exit loop/program

问题描述

这是一个简单的温度转换器（华氏温度到摄氏温度，开元价格为b
）。使用gcc 4.0。


用户应该输入q或任何其他非字符来退出

程序。


此代码出现问题：

一旦程序启动，我输入''q''。它挂了。

然后再次运行它。输入一个数字，它执行正常。但是当我输入

q时，它会重复上一个数字并且它没有注意输入的字母

。

关于如何修复它的任何想法？提前谢谢。


#include< stdio.h>


const double F_TO_CELS_ONE_EIGHT = 1.8;

const double F_TO_CELS_THIRTYTWO = 32.0;

const double C_TO_KELVIN = 273.16;


void Temperatures（double f_temp）;


int main（void）{


double f_temp;

char quit;

while（quit！=" q" ）{

printf（输入华氏温度（q退出）：

"）;

quit = getchar（）;

scanf（"％lf"，& f_temp）;

Temperatures（f_temp）;

}

printf（" \ nbyby！"）;

返回0;

}


void Temperatures（double f_temp ）{


双摄氏度，开尔文;


摄氏度=（F_TO_CELS_ONE_EIGHT * f_temp）+ F_TO_CELS_THIRTYTWO;

开尔文=摄氏+ C_TO_KELVIN;


printf（华氏度：％。2f \ n，f_temp）;

printf（摄氏度：％。2f \ n，摄氏度）;

printf（开尔文度：％。2f \ n，开尔文）;

}

解决方案

icarus说：


< snip>

关于如何修复它的任何想法？

是。

#include< stdio.h>


const double F_TO_CELS_ONE_EIGHT = 1.8;

const double F_TO_CELS_THIRTYTWO = 32.0;

const double C_TO_KELVIN = 273.16;


void Temperatures（double f_temp）;


int main（void）{


double f_temp;

char quit ;

int quit; / * getchar返回int，而不是char * /

>


while（quit！=" q"） {

while（quit！=''q''）{


" q"是一个字符串文字。你想要与一个角色进行比较，而不是一个

字符串。

printf（"以华氏温度输入温度（q退出）：

"）;

quit = getchar（）;

scanf（"％lf"，& f_temp）;

坏主意。假设您输入字符2，1，2（沸点

水）和换行符。第一个2存储在退出中，

将1和2转换为12，存储在f_temp中。

现在，12华氏度比沸点冷得多（事实上，它比冰冻低20美元）。


我建议捕获数据作为一个字符串并检查第一个

字符。如果它不是''q''，请将字符串交给sscanf（或者，更好的是

仍然是strtod）进行转换。


- -

Richard Heathfield< http://www.cpax.org.uk>

电子邮件：-http：// www。 + rjh @

谷歌用户：< http://www.cpax.org.uk/prg/writings/googly.php>

Usenet是一个奇怪的放置" - dmr 1999年7月29日

icarus写道，On 09/05/08 21:57：

Hi ，这是一个简单的温度转换器（华氏温度到摄氏温度），开元温度为b
。使用gcc 4.0。


用户应该输入q或任何其他非字符来退出

程序。


此代码出现问题：

一旦程序启动，我输入''q''。它挂了。

然后再次运行它。输入一个数字，它执行正常。但是当我输入

q时，它会重复上一个数字并且它没有注意输入的字母

。


关于如何修复它的任何想法？提前谢谢。


#include< stdio.h>


const double F_TO_CELS_ONE_EIGHT = 1.8;

const double F_TO_CELS_THIRTYTWO = 32.0;

const double C_TO_KELVIN = 273.16;


void Temperatures（double f_temp）;


int main（void）{


double f_temp;

char quit;

这里有什么价值，因为它从未被赋值？

while（quit） ！=" q"）{

printf（"输入华氏温度（q退出）：

"）;

quit = getchar（）;

所以你已经阅读了一个字符，现在你去调用scanf无论是什么

suer输入！您在该行末尾输入的换行符会发生什么变化？

scanf（"％lf"，& f_temp）;

< snip>


scanf返回一个值，这是什么意思？


你需要首先考虑用户输入是如何工作的，看起来好像

你在写这篇文章之前没有想到它。我建议

使用fgets输入然后检查并使用输入的内容。

-

Flash Gordon

你需要首先考虑用户输入是如何工作的，它看起来像

你在写这篇文章之前没有想到它。我建议

使用fgets输入然后检查并使用输入的内容。

-

Flash Gordon

是啊是啊是的闪光戈登，给我讲课。


如果你这么体贴，

为什么要穿那么你对可能的解决方案进行详细说明了吗？


5月9日上午11点48分，Flash Gordon< s ... @ flash- gordon.me.ukwrote：

icarus写道，On 09/05/08 21:57：

这是一个简单的温度转换器（华氏温度到摄氏温度，开元价格为b
）。使用gcc 4.0。

用户应该输入q或任何其他非字符来退出

程序。

此代码出现问题：

一旦程序启动，我输入''q''。它挂了。

然后再次运行它。输入一个数字，它执行正常。但是当我输入

q时，它会重复上一个数字并且它不会注意输入的字母

。

关于如何修复它的任何想法？提前致谢。

#include< stdio.h>

const double F_TO_CELS_ONE_EIGHT = 1.8;

const double F_TO_CELS_THIRTYTWO = 32.0;

const double C_TO_KELVIN = 273.16;

void Temperatures（double f_temp）;

int main（void）{

double f_temp;

char quit;

因为它从未被赋值，所以退出这里有什么值？

while（quit ！=" q"）{

printf（"输入华氏温度（q退出）：

"）;

quit = getchar（）;

所以你已经阅读了一个角色，现在你去打电话给scanf无论是什么

suer输入！您在该行末尾输入的换行符会发生什么变化？

scanf（"％lf"，& f_temp）;

< snip>


scanf返回一个值，这是什么意思？


你需要首先考虑用户输入是如何工作的，看起来好像

你在写这篇文章之前没有想到它。我建议

使用fgets输入然后检查并使用输入的内容。

-

Flash Gordon

Hi, this is a simple temperature converter (Fahrenheit to Celsius to
Kelvin). Using gcc 4.0.

The user is supposed to enter q or any other non-character to exit the
program.

Problem with this code:
I enter ''q'' as soon as the program starts. It hangs.
Then run it again. Enter a number, it executes fine. But when I enter
q, it repeats last number and it doesn''t ''pay attention'' to the letter
entered.
Any ideas on how can I fix it? thanks in advance.

#include <stdio.h>

const double F_TO_CELS_ONE_EIGHT = 1.8;
const double F_TO_CELS_THIRTYTWO = 32.0;
const double C_TO_KELVIN = 273.16;

void Temperatures(double f_temp);

int main(void){

double f_temp;
char quit;
while (quit != "q"){
printf("Enter temperature in Fahrenheit (q to quit):
");
quit = getchar();
scanf("%lf", &f_temp);
Temperatures(f_temp);
}
printf("\nbye!");
return 0;
}

void Temperatures(double f_temp){

double celsius, kelvin;

celsius = (F_TO_CELS_ONE_EIGHT * f_temp) + F_TO_CELS_THIRTYTWO;
kelvin = celsius + C_TO_KELVIN;

printf("Fahrenheit degrees: %.2f\n", f_temp);
printf("Celsius degrees: %.2f\n", celsius);
printf("Kelvin degrees: %.2f\n", kelvin);
}

解决方案

icarus said:

<snip>

Any ideas on how can I fix it?

Yes.

#include <stdio.h>

const double F_TO_CELS_ONE_EIGHT = 1.8;
const double F_TO_CELS_THIRTYTWO = 32.0;
const double C_TO_KELVIN = 273.16;

void Temperatures(double f_temp);

int main(void){

double f_temp;
char quit;

int quit; /* getchar returns int, not char */

>

while (quit != "q"){

while(quit != ''q''){

"q" is a string literal. You want to compare with a character, not a
string.

printf("Enter temperature in Fahrenheit (q to quit):
");
quit = getchar();
scanf("%lf", &f_temp);

Bad idea. Let''s say you enter the characters ''2'', ''1'', ''2'' (boiling point
of water) and a newline character. The first ''2'' is stored in quit,
leaving ''1'' and ''2'' to be converted into 12 which is stored in f_temp.
Now, 12 Fahrenheit is a lot colder than boiling point (in fact, it''s 20
below freezing).

I recommend capturing the data as a string and inspecting the first
character. If it''s not ''q'', hand the string off to sscanf (or, better
still, strtod) for conversion.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

icarus wrote, On 09/05/08 21:57:

Hi, this is a simple temperature converter (Fahrenheit to Celsius to
Kelvin). Using gcc 4.0.

The user is supposed to enter q or any other non-character to exit the
program.

Problem with this code:
I enter ''q'' as soon as the program starts. It hangs.
Then run it again. Enter a number, it executes fine. But when I enter
q, it repeats last number and it doesn''t ''pay attention'' to the letter
entered.
Any ideas on how can I fix it? thanks in advance.

#include <stdio.h>

const double F_TO_CELS_ONE_EIGHT = 1.8;
const double F_TO_CELS_THIRTYTWO = 32.0;
const double C_TO_KELVIN = 273.16;

void Temperatures(double f_temp);

int main(void){

double f_temp;
char quit;

What value does quit have here since it has never been assigned a value?

while (quit != "q"){
printf("Enter temperature in Fahrenheit (q to quit):
");
quit = getchar();

So you have read one character, now you go and call scanf whatever the
suer input! What happens to the newline you enter at the end of the line?

scanf("%lf", &f_temp);

<snip>

scanf returns a value, what does it mean?

You need to start by thinking about how user input works, it looks like
you did not think about it before writing this. I would suggest that
using fgets for input and then checking and using what was entered.
--
Flash Gordon

You need to start by thinking about how user input works, it looks like

you did not think about it before writing this. I would suggest that
using fgets for input and then checking and using what was entered.
--
Flash Gordon

yeah yeah yeah flash gordon, spare me the lecture.

if you are so thoughtful,
why don''t you elaborate a little more on your possible solution then?


On May 9, 11:48 am, Flash Gordon <[e-mail]:

icarus wrote, On 09/05/08 21:57:

Hi, this is a simple temperature converter (Fahrenheit to Celsius to
Kelvin). Using gcc 4.0.

The user is supposed to enter q or any other non-character to exit the
program.

Problem with this code:
I enter ''q'' as soon as the program starts. It hangs.
Then run it again. Enter a number, it executes fine. But when I enter
q, it repeats last number and it doesn''t ''pay attention'' to the letter
entered.

Any ideas on how can I fix it? thanks in advance.

#include <stdio.h>

const double F_TO_CELS_ONE_EIGHT = 1.8;
const double F_TO_CELS_THIRTYTWO = 32.0;
const double C_TO_KELVIN = 273.16;

void Temperatures(double f_temp);

int main(void){

double f_temp;
char quit;

What value does quit have here since it has never been assigned a value?

while (quit != "q"){
printf("Enter temperature in Fahrenheit (q to quit):
");
quit = getchar();

So you have read one character, now you go and call scanf whatever the
suer input! What happens to the newline you enter at the end of the line?

scanf("%lf", &f_temp);

<snip>

scanf returns a value, what does it mean?

You need to start by thinking about how user input works, it looks like
you did not think about it before writing this. I would suggest that
using fgets for input and then checking and using what was entered.
--
Flash Gordon

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