How can I read the enter key in a loop multiple times?
I've tried the following with no result.
char c;
for (i=0; i<n; i++){
c = getchar ();
fflushstdin ();
if (c == '\n'){
//do something
}
}
And fflushstdin:
void fflushstdin (){
int c;
while ((c = fgetc (stdin)) != EOF && c != '\n');
}
If I read any other character instead of enter key it works perfect, but with enter key In some iterations I have to press the enter 2 times.
Thanks.
EDIT: I'm executing the program through putty on windows and the program is running on a virtualized linux mint on virtual box.
Why do you call fflushstdin()? If fgetc() returns something different from \n, that character is completely dropped.
This should work:
char prev = 0;
while(1)
{
char c = getchar();
if(c == '\n' && prev == c)
{
// double return pressed!
break;
}
prev = c;
}
Try
if (ch == 13) {
//do something
}
ASCII value of enter is 13, sometimes \n won't work.
You should go with:
char c;
for (i=0; i<n; i++){
c = getchar ();
fflushstdin ();
if (c == 13){
//do something
}
}
since 13 is ASCII code for Enter key.
You always executing getchar twice (even when there is no need for that). Try limiting calls to fflushstdin:
char c;
for (i=0; i<n; i++){
c = getchar ();
if ((c != EOF) && (c != '\n')) fflushstdin ();
if (c == '\n'){
//do something
}
}
Related
I don't understand why the printf() call after the while loop does not get executed?
int main(){
while((getchar()) != EOF){
characters ++;
if (getchar() == '\n'){
lines++;
}
}
printf("lines:%8d\n",lines);
printf("Chars:%8d",characters);
return 0;
}
I think you are trying to do that
#include<stdio.h>
int main()
{
int characters=0,lines=0;
char ch;
while((ch=getchar())!= EOF)
{
if (ch == '\n')
lines++;
else
{
characters++;
while((ch=getchar())!='\n'&&ch!=EOF); //is to remove \n after a character
}
}
printf("lines:%8d\n",lines);
printf("Chars:%8d",characters);
return 0;
}
Output:
a
s
d
f
^Z
lines: 1
Chars: 4
Process returned 0 (0x0) execution time : 8.654 s
Press any key to continue.
Note: ^Z(ctrl+z) is to send EOF to stdin (in windows)
You have to be careful of you're treatment in the while loop. Indeed, you are missing every caracter read in your while statement. You have to save this input, in order to use it afterwards.
The proper syntax would be while(( c = getchar()) != EOF)
You are probably looking for something like this:
#include <stdio.h>
int main()
{
int characters = 0;
int lines = 0;
int c;
while ((c = getchar()) != EOF) {
characters++;
if (c == '\n') {
lines++;
characters--; // ignore \n
}
}
printf("lines: %8d\n", lines);
printf("Chars: %8d", characters);
return 0;
}
while ((c = getchar()) != EOF) might look a bit confusing.
Basically it calls getchar, puts the returned valuee into c ands then checks if c equals EOF.
I am trying to take t (test cases) strings as inputs in C. Every string ends with a # and it can have spaces.
I am using getchar and some while loops but I am not able to achieve what I want.
int t;
scanf("%d",&t);
while(t>0){
char expression[100];
char c;
int i=0;
while(1){
c = getchar();
if(c == '#'){
break;
}
else{
expression[i]=c;
i++;
}
}
t--;
printf("%d\n",i);
for(int j=0;j<i;j++){
printf("%c",expression[j]);
}
}
What I am trying to achieve is if # is encountered I want to ignore whatever is after It.
My input:
1
test#wtf
Output:
5
test
So in case of 1 test case it is working fine.
But when I give try this.
2
test#wtf
test#
The corresponding outs are:
5
test
and
8
wtf
test
As you can see the second output should be test and length should be 5 but it is not so.
In order to ignore text after #, you'll have to consume those characters using getchar() and ignore them till you encounter a new line character '\n'.
So, after you exit the inner while loop, you need to add the following code
while(1) {
c = getchar();
if(c == '\n'){
break;
}
}
You can do it this way, you process all characters, once you get a '#' you keep reading characters without adding them to the array and you get out of the outer loop once you get a new line character '\n'.
while (--t > 0)
{
int i,s,c;
char exp[100];
s = 0;
while (s < 100 && (c = getchar()) != '#')
exp[s++] = c;
while ((c = getchar()) != '\n')
;
printf("%d\n", s);
i = -1;
while (++i < s)
printf("%c", exp[i]);
printf("\n");
}
I've encountered a problem when validating a single-char scanf input in C and I cannot find an existing solution that works...
The scenario is: a method is taking a single letter 'char' type input and then validating this input, if the criteria is not met, then pops an error message and re-enter, otherwise return this character value.
my code is:
char GetStuff(void)
{
char c;
scanf("%c", &c);
while(c != 'A' || c != 'P')
{
printf("invalid input, enter again (A for AM or P for PM): ");
scanf ("%c", &dtChar);
}
return c;
}
however, i got the infinite loop of error message no matter what input I type in. I read some other posts and guess it's the problem that %c specifier does no automatically get rid of the newline when I hit enter, and so far I have tried:
putting a white space before/after %c like:
scanf(" %c", &c);
write a separate method or include in this GetStuff method to clean the newline like:
void cleanBuffer(){
int n;
while((n = getchar()) != EOF && n != '\n' );
}
Can anyone help me with this problem please? Thank you in advance.
Please consider the following snippet:
#include <stdio.h>
#include <ctype.h>
char GetStuff(void)
{
char c;
do {
printf("Please enter A for AM or P for PM: ");
scanf ("%c", &c);
// clean input buffer (till the end of line)
while(getchar()!='\n');
} while(toupper(c) != 'A' && toupper(c) != 'P');
return c;
}
int main(void)
{
printf("Your input is'%c'\n", GetStuff());
return 0;
}
Note the points:
condition while(c != 'A' || c != 'P') will be always true (just because one character cannot be 'A' and 'P' at the same time), so use while(c != 'A' && c != 'P') instead
No need for two scanf if you use do..while loop
After entering a char with scanf it is recommended to clean all characters from buffer, e.g. with while(getchar()!='\n'); (this will clean all input including incorrect and redundant characters)
use toupper to avoid making 4 comparison (actually single c=toupper(c) inside loop can minimize your while as while(c != 'A' && c != 'P') )
UPDATE:
To add message "Invalid input" and adding some other useful improvement subjected befor... new code is as:
#include <stdio.h>
#include <ctype.h>
void CleanBuffer(){
int n;
while((n = getchar()) != EOF && n != '\n' );
}
char GetStuff(void)
{
char c;
do {
printf("Please enter A for AM or P for PM: ");
scanf (" %c", &c);
c = toupper(c); // here letter become uppercase
CleanBuffer();
} while( (c != 'A' && c != 'P')?printf("Invalid input! "):0 );
return c;
}
int main(void)
{
printf("You have entered: %c\n", GetStuff());
return 0;
}
Note: function will return 'A' or 'P' in uppercase, so if this is not needed change the code as in example before update (use two toupper and do not change c after scanf). Also you can use tolower as an option (of course with comparing to 'a' and 'p').
#include <stdio.h>
char GetStuff(void) {
char c;
scanf("%c", &c);
getchar();
while ((c != 'A') && (c != 'a') && (c != 'P') && (c != 'p')) {
printf("invalid input, enter again (A for AM or P for PM): ");
scanf ("%c", &c);
getchar();
}
return c;
}
int main(void) {
printf("Calling GetStuff()...\n");
char x = GetStuff();
printf("User entered %c\n", x);
return 0;
}
You are using while (c != 'A' || c != 'P') as your loop conditional, but this will always return true. What you meant to use is the && "and" operator, instead of the || "or" operator.
Also, call getchar() after your scanf statements, to capture the newline. This should work the way you want it to.
Inside loop you are taking input in dtChar but your loop condition checks variable c which is not updated in the loop, that is causing infinite loop
Also you would change your condition
while(c != 'A' || c != 'P')
to
while(c != 'A' && c != 'P')
If you want user to enter either 'A' or 'P'
Another possible solution. As others mentioned the condition was to be done with &&. Anyway the big problem is how to remove what's left on the console input line. Since the console works by lines, we remove everything up to the next '\n'. If the user already left something on the input line before calling GetStuff(), it would be useful to add a call to SkipRestOfTheLine() before the while loop.
In general I suggest to start with a while(1) loop, before making it nicer (such as in the cleanBuffer() you posted).
#include <stdlib.h>
#include <stdio.h>
void SkipRestOfTheLine(void)
{
while (1) {
int c = fgetc(stdin);
if (c == EOF || c == '\n')
break;
}
}
char GetStuff(void)
{
while (1) {
int c = fgetc(stdin);
if (c == EOF)
exit(EXIT_FAILURE); // Deal with this case in an appropriate way
if (c == 'A' || c == 'P')
return c;
printf("invalid input, enter again (A for AM or P for PM): ");
SkipRestOfTheLine();
}
}
int main(void)
{
char c = GetStuff();
return 0;
}
try this,
char GetStuff(void)
{
char c;
scanf("%c", &c);
while (((c != 'A') || (c != 'a')) && ((c != 'P') || (c != 'p'))==1)
{
printf("invalid input, enter again (A for AM or P for PM): ");
scanf ("%c", &dtChar);
}
return c;
}
I hope this works, some time because of not given proper bracket it is stuck in the loop.
#include <stdio.h>
int main(){
char c;
do{
printf("invalid input, enter again (A for AM or P for PM): ");
scanf ("%s", &c);
}while ((c != 'A') && (c != 'P'));
return 0;
}
I have just started learning C, been reading a C textbook by Keringhan and Ritchie. There was this example in the textbook, counting characters from user input. Here's the code:
#include <stdio.h>
main()
{
long nc;
nc = 0;
while(getchar() != EOF) {
if (getchar() != 'q')
++nc;
else
break;
}
printf("%ld\n", nc);
}
The problem is, when I execute the code, if I input only one character per line, when I input "q" to break, it doesn't do so. I have to type some word per line, only after that it will break the loop. Also, it only counts the half of the characters of the word. I.e. if I input
a
b
russia
it will only print '5' as final result.
Could you please explain to me why is this happening?
This works, but only when you finish off with an Enter. So, this will count the characters until the first "q" appears. That is just how getchar() and getc(stdin) work.
#include <stdio.h>
int main() {
char c = 0;
long count = 0;
short int count_linebreak = 1; // or 0
while((c = getchar()) != EOF) {
if(c != 'q' && (count_linebreak || (!count_linebreak && c != '\n'))) {
++count;
}else if(c == 'q') {
printf("Quit\n");
break;
}
}
printf("Count: %ld\n",count);
return 0;
}
A StackOverflow question about reading stdin before enter
C read stdin buffer before it is submit
Im writing a simple program to count the number of character user is entered, and i wrote an if to check wether there is a newline but still printing it..
the code:
#include <stdio.h>
int main()
{
char ch;
int numberOfCharacters = 0;
printf("please enter a word, and ctrl + d to see the resault\n");
while ((ch = getchar()) != EOF)
{
if (numberOfCharacters != '\n')
{
numberOfCharacters++;
}
}
printf("The number of characters is %d", numberOfCharacters);
return 0;
}
what am i doing wrong?
Think about this line:
if (numberOfCharacters != '\n')
how can it make sense? You are comparing the number of characters read so far with a newline, it's like comparing apples to oranges and surely won't work. It's another variable that you should check...
Change your loop to this.
while ((ch = getchar()) != EOF)
{
if(ch != '\n')
numberOfCharacters++;
}