getchar() is not working in the below program, can anyone help me to solve this out. I tried scanf() function in place of getchar() then also it is not working.
I am not able to figure out the root cause of the issue, can anyone please help me.
#include<stdio.h>
int main()
{
int x, n=0, p=0,z=0,i=0;
char ch;
do
{
printf("\nEnter a number : ");
scanf("%d",&x);
if (x<0)
n++;
else if (x>0)
p++;
else
z++;
printf("\nAny more number want to enter : Y , N ? ");
ch = getchar();
i++;
}while(ch=='y'||ch=='Y');
printf("\nTotal numbers entered : %d\n",i);
printf("Total Negative Number : %d\n",n);
printf("Total Positive number : %d\n",p);
printf("Total Zero : %d\n",z);
return 0 ;
}
The code has been copied from the book of "Yashvant Kanetkar"
I think, in your code, the problem is with the leftover \n from
scanf("%d",&x);
You can change that scanning statement to
scanf("%d%*c",&x);
to eat up the newline. Then the next getchar() will wait for the user input, as expected.
That said, the return type of getchar() is int. You can check the man page for details. So, the returned value may not fit into a char always. Suggest changing ch to int from char.
Finally, the recommended signature of main() is int main(void).
That's because scanf() left the trailing newline in input.
I suggest replacing this:
ch = getchar();
With:
scanf(" %c", &ch);
Note the leading space in the format string. It is needed to force scanf() to ignore every whitespace character until a non-whitespace is read. This is generally more robust than consuming a single char in the previous scanf() because it ignores any number of blanks.
When the user inputs x and presses enter,the new line character is left in the input stream after scanf() operation.Then when try you to read a char using getchar() it reads the same new line character.In short ch gets the value of newline character.You can use a loop to ignore newline character.
ch=getchar();
while(ch=='\n')
ch=getchar();
When you using scanf getchar etc. everything you entered stored as a string (char sequence) in stdin (standard input), then the program uses what is needed and leaves the remains in stdin.
For example: 456 is {'4','5','6','\0'}, 4tf is {'4','t','f','\0'} with scanf("%d",&x); you ask the program to read an integer in the first case will read 456 and leave {'\0'} in stdin and in the second will read 4 and leave {''t','f',\0'}.
After the scanf you should use the fflush(stdin) in order to clear the input stream.
Replacing ch = getchar(); with scanf(" %c", &ch); worked just fine for me!
But using fflush(stdin) after scanf didn't work.
My suggestion for you is to define a Macro like:
#define __GETCHAR__ if (getchar()=='\n') getchar();
Then you can use it like:
printf("\nAny more number want to enter : Y , N ? ");
__GETCHAR__;
I agree that it is not the best option, but it is a little bit more elegant.
Add one more line ch = getchar();
between scanf("%d",&x); and ch = getchar();
then your code work correctly.
Because when you take input from user, in this time you press a new line \n after the integer value then the variable ch store this new line by this line of code ch = getchar(); and that's why you program crash because condition can not work correctly.
Because we know that a new line \n is also a char that's why you code crash.
So, for skip this new line \n add one more time ch = getchar();
like,
ch = getchar(); // this line of code skip your new line when you press enter key after taking input.
ch = getchar(); // this line store your char input
or
scanf("%d",&x);
ch = getchar(); // this line of code skip your new line when you press enter key after taking input.
pieces of code work correctly.
Related
void kmmil()
{
int x, y;
printf("a.KM TO MILS\n");
printf("b.MILS TO KM\n");
char c;
scanf("%c", &c);
printf("this is the value %c", c);
}
output:
this is the value (blank)
end;
If the scanf "doesn't work" it usually does but not in a way we intended to. If you have another scanf in your code, that for example scans a number. You type in your terminal something like 123 and hit enter to confirm. That enter however stays in the input and waits to be scanned by something. This is probably why your scanf "doesn't work". Onto the solution to that:
I suggest you clear your input. You can do this in at least
scanf("%*[^\n]"); // scan and delete everything until newline character
scanf("%*c"); // scan and delete one more character (newline)
or
while(getchar() != '\n'); // get characters until newline (note that newline is deleted this way too!)
I have wrote a small code to get value from Fahrenheit to Celsius. I wanted to keep inputting data until I press any other key than 'y'. But this loop doesn't work that way and stops after one iteration.
#include <stdio.h>
int main()
{
char ch='y';
int far, cen;
do {
printf("again\n");
scanf("%d",&far);
//cen = (5.0/9.0)*(far-32);//integer division will truncate to zero so we can make 5/9 to 5.0 / 9.0
cen = (5*(far-32))/9;//or this way we can use this formula
printf("\n%d\t%d",far, cen);
printf("ch=%c",ch);
scanf("%c",&ch);
}while(ch == 'y');
return 0;
}
What is the problem here?
P.S
I added a line and made a new code like this
#include <stdio.h>
int main()
{
char ch='y';
int far, cen;
do {
printf("again\n");
scanf("%d",&far);//here we press carriage return. this value is in stdin
//cen = (5.0/9.0)*(far-32);//integer division will truncate to zero so we can make 5/9 to 5.0 / 9.0
cen = (5*(far-32))/9;//or this way we can use this formula
printf("\n%d\t%d",far, cen);
scanf("%c",&ch);//putting a space before %c makes the newline to be consumed and now it will work well
if((ch == '\r')|| (ch == '\n'))
printf("1\n");
printf("ch=%c",ch);//this takes the carriage return in stdin buffer
}while(ch == 'y');
return 0;
}
I need to know carriage return here is \r or \n?
When the value for scanf("%d",&far); is entered and press enter, the scanf stores the carriage return in the buffer. When it encounters the second scanf in the code scanf("%c",&ch); it takes the carriage return present in the buffer as the input to 'ch'. So it doesn't wait for the user input.
Please have a look at the post here
As indicated in one of the reply the solution is to put a space in scanf
scanf(" %c",&ch);
You should always check the return value of scanf. Your first use of scanf may fail if the user does not enter a valid integer, in which case, you are using far without initialising it (which is undefined behaviour). scanf returns the number of items that were successfully scanned. If you are requesting scanf to scan one integer, then it should return 1 if it successfully managed to scan an integer.
int scanresult = scanf("%d", &far);
if (scanresult != 1)
{
puts("Invalid input or unexpected end of input");
return 1;
}
In addition, the %c conversion specifier is unique in that it does not cause scanf to gobble up any preceding whitespace unlike the other conversion specifiers. To force scanf to gobble up the whitespace (such as linefeeds, carriage returns, spaces, tabs etc), simply put a space character before the %c, e.g.
scanresult = scanf(" %c", &ch);
For scanf, the space character is actually a directive to parse and skip all whitespace.
This is because of the previous newline character remaining in the buffer. You can simply replace scanf by this line:
while((ch = getchar()) == '\n');
You'll be needing the same technique in combination with ungetc() in many occasions.
Add fflush() function, just above scanf("%c", &ch). Because buffer of CONSOLE INPUT stores characters that not returned to program. Which is ENTER pressed in previous scanf:
#include <stdio.h>
int main() {
char ch='y';
int far, cen;
do {
printf("again\n");
scanf("%d",&far);
//cen = (5.0/9.0)*(far-32);//integer division will truncate to zero so we can make 5/9 to 5.0 / 9.0
cen = (5*(far-32))/9;//or this way we can use this formula
printf("\n%d\t%d",far, cen);
printf("ch=%c",ch);
scanf("%c",&ch); // This scanf will be ignored, because loads last
// character from buffer that can be recognized
// by scanf which is pressed "ENTER" from previous scanf
printf("%d", ch) // Shows 10, which is ASCII code of newline
fflush(stdin); // Clear buffer
scanf("%c",&ch); // Now it will prompt you to type your character.
// printf("%c"ch); //Without fflush, it must show 10, which is \n code
}while(ch == 'y');
return 0;
}
if after Y you press "space" or "return" this is the character you will find in %C
Currently im trying to learn simple C Programs. But, i came into this situation :
#include<conio.h>
#include<stdio.h>
void main()
{
char c;
int tryagain=1;
while(tryagain>0){
printf("Enter the Character : ");
scanf("%c",&c);
printf("You entered the character \"%c\" and the ascii value is %d",c,c);
getch();
clrscr();
tryagain=0;
printf("You want to Trry again Press 1 : ");
scanf("%d",&tryagain);
clrscr();
}
}
The program is fine when user first enter a character. And, when it ask to continue. And, user enter 1 then it is behaving weired. It automatically input blank character and prints the ascii and goto the same place.
How can i resolve this? And, specially, Why is the reason for this?
And, Im sorry about my poor english!
Thank you in Advance.
When you use
scanf("%d",&tryagain);
the number is read into tryagain but the newline character, '\n', is still left on the input stream. The next time you use:
scanf("%c",&c);
the newline character is read into the c.
By using
scanf("%d%*c",&tryagain);
the newline is read from the input stream but it is not stored anywhere. It is simply discarded.
The issue is that you are reading a single number in the second scanf, but user inputs more than a single number there, the user also input a new line character by pressing .
User enters "1\n". Your scanf reads "1", leaving out "\n" in the input stream. Then the next scanf that reads a character reads "\n" from the stream.
Here is the corrected code. I use getc to discard the extra new line character that is there.
#include <stdio.h>
void main()
{
char c;
int tryagain = 1;
while (tryagain > 0) {
printf("Enter a character: ");
scanf("%c", &c);
printf("You entered the character \"%c\" and the ascii value is %d\n", c, c);
tryagain = 0;
printf("If you want to try again, enter 1: ");
scanf("%d", &tryagain);
// get rid of the extra new line character
getc(stdin);
}
}
Also, as a side note, you use conio.h which is not part of standard C, it's MS-DOS header file, thus it's not portable C you are writing. I have removed it from my code, but you might wish to keep it.
My program which finds prime factors is all set...the only thing left that I need to do is this type of output:
Do you want to try another number? Say Y(es) or N(o): y
//asks for another number (goes through the program again)
Do you want to try another number? Say Y(es) or N(o): n
//Thank you for using my program. Good Bye!
I have my attempt at this below...When I type n it does the correct output. But if I type 'y' it just says the same thing n does....How can I loop the entire program without putting the code for the program inside this while loop I have? So when I press y it goes through the program again?
int main() {
unsigned num;
char response;
do{
printf("Please enter a positive integer greater than 1 and less than 2000: ");
scanf("%d", &num);
if (num > 1 && num < 2000){
printf("The distinctive prime facters are given below: \n");
printDistinctPrimeFactors(num);
printf("All of the prime factors are given below: \n");
printPrimeFactors(num);
}
else{
printf("Sorry that number does not fall within the given range. \n");
}
printf("Do you want to try another number? Say Y(es) or N(o): \n");
response = getchar();
getchar();
}
while(response == 'Y' || response == 'y');
printf("Thank you for using my program. Goodbye!");
return 0;
} /* main() */
The problem is probably, that you're getting something that isn't y from getchar and the loop exits, as the condition is not matched.
getchar() may use a buffer, so when you type 'y' and hit enter, you will get char 121 (y) and 10 (enter).
Try the following progam and see what output you get:
#include <stdio.h>
int main(void) {
char c = 0;
while((c=getchar())) {
printf("%d\n", c);
}
return 0;
}
You will see something like this:
$ ./getchar
f<hit enter>
102
10
What you can see is that the keyboard input is buffered and with the next run of getchar() you get the buffered newline.
EDIT: My description is only partially correct in terms of your problem. You use scanf to read the number you're testing against. So you do: number, enter, y, enter.
scanf reads the number, leaves the newline from your enter in the buffer, the response = getchar(); reads the newline and stores the newline in response, the next call to getchar() (to strip the newline I described above) gets the 'y' and your loop exits.
You can fix this by having scanf read the newline, so it doesn't linger in the buffer: scanf("%d\n", &number);.
When reading input using scanf (when you enter your number above), the input is read after the return key is pressed but the newline generated by the return key is not consumed by scanf.
That means your first call to getchar() will return the newline (still sitting in the buffer), which is not a 'Y'.
If you reverse your two calls to getchar() - where the second one is the one you assign to your variable, your program will work.
printf("Do you want to try another number? Say Y(es) or N(o): \n");
getchar(); // the newline not consumed by the scanf way above
response = getchar();
just put getchar() after scanf statement of yours that will eat the unnecessary '\n' from buffer...
As others have stated, there is a single '\n' character in the input stream left over from your earlier call to scanf().
Fortunately, the standard library function fpurge(FILE *stream) erases any input or output buffered in the given stream. When placed anywhere between your calls to scanf() and getchar(), the following will rid stdin of anything left in the buffer:
fpurge(stdin);
I am having trouble with inserting string in to char variable. Problem appeares when I put it into function. When I debug my program, it displays printf but it skipes gets
here is my code:
int uloz(SPRAVA *p){
char string[200];
printf("Your message here: ");
gets(string);
printf("You have entered: %s", string);
getchar();
return 0;
}
Use scanf(" %30[^\n]%*c",string);
[^\n] will accept anything till \n.
30 will limit the length of number of characters to max 30.
initial space(' ') will consume any \n already in stdin stream. (optional & i have not verified it)
& Finally, %*c will consume \n pressed after entering string.
I think, scanf(" %30[^\n]%*[^\n]%*c",string); would be a good option, to discard remaining characters (after 30) that were entered. However this is completely unverified. Just added as a possible idea. Test before use. :-)
There's a newline in the stdio buffer (left over by some previous scanf) so gets is immediately satisfied.
There's no easy way to fix it but you could try discarding input, before the fgets:
while((c = getchar()) != '\n' && c != EOF)
/* discard the character */;
The true solution is to avoid mixing scanf and fgets.
Use fgets instead of gets.