Problem with repeats in the output

This is a discussion on Problem with repeats in the output within the C Programming forums, part of the General Programming Boards category; At first I want to say, that I'm a beginner and I'm just curious, why is the result in the ...

  1. #1
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    Problem with repeats in the output

    At first I want to say, that I'm a beginner and I'm just curious, why is the result in the output doubled and due what it's so.
    Code:
    #include <stdio.h>
    
    int main(void)
    {
        char ch;
        
        do {
            
            printf("Enter char: \n");
            ch = getchar();
            if(ch == 'q') break; 
            printf("Hello World ! \n");
            
            
        } while(ch!='q');
        
        
    }
    And this is the output:
    Code:
    Enter char: 
    a
    Hello World ! 
    Enter char: 
    Hello World ! 
    Enter char:

  2. #2
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    When you press 'a' then <enter>, you actually put two characters in the input buffer, the 'a' and a newline. You need to flush the input buffer: Cprogramming.com FAQ > Flush the input buffer.

  3. #3
    Registered User claudiu's Avatar
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    You also need to return 0.
    1. Get rid of gets(). Never ever ever use it again. Replace it with fgets() and use that instead.
    2. Get rid of void main and replace it with int main(void) and return 0 at the end of the function.
    3. Get rid of conio.h and other antiquated DOS crap headers.
    4. Don't cast the return value of malloc, even if you always always always make sure that stdlib.h is included.

  4. #4
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    Thank you !

  5. #5
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    OK I'm curious. I am guilty of using a scanf and fflush (stdin); which everyone tells me is not good. However this program can be fixed in about .2 seconds doing it that way.

    I've been playing with the FAQ method of clearing the input buffer and cannot get a smooth run of this simple program. Here is where I'm at with the other posters program:

    Code:
    int _tmain(int argc, _TCHAR* argv[])
    {
    
    
    
    
    
      char   ch;
      char  buf[1];
      
      do
      {
    	
    	
    	printf ("Enter a Char: ");
    	ch = getchar();
    	while ((ch = getchar()) != '\n' && ch != EOF);
    	if (fgets(buf, sizeof(buf), stdin))
      {
      printf ("Hello world!\n");
      }
     
      
      }while (ch != 'q');
      return 0;
    }
    This program will run as expected but it never breaks the loop. My guess is that's because the input buffer is clear before the do while gets to the while part so it never sees the q. How do you get around this.

  6. #6
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    My gosh... all that just to ignore a character?

    Code:
    do
      { if (ch != '\n')
          printf("Enter a character : ");
         ch = getchar();
        if (ch != '\n')
          printf(" You entered : %c",ch); }
    while (tolower(ch) ! = 'q');
    Let the thing houseclean itself.

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    Nov 2007
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    14,185
    Whenever you get to the end of your do-while loop, ch must needs be '\n'. Did you intend to compare buf[0]? Or, if you are looking for the char that was entered, then use a different char variable.

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