getchar() problem

This is a discussion on getchar() problem within the C Programming forums, part of the General Programming Boards category; hey. when I use (ans!='d') the printf("sum\n") prints the line twice and then the getchar() function is beeing used. Code: ...

  1. #1
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    getchar() problem

    hey. when I use (ans!='d') the printf("sum\n") prints the line twice and then the getchar() function is beeing used.

    Code:
    #include <stdio.h>
    main()
     {
       char ans;
       ans= getchar();
       while(ans!='d')
       {
         printf("sum\n");
         ans= getchar();
       }
     }
    on the other hand when I use (ans=='d') then the second ans= getchar() function doesn't work. the program just ends.
    what am I not doing correct?

    dh

  2. #2
    Code Goddess Prelude's Avatar
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    >main()
    Code:
    int main ( void )
    is the correct definition of main without arguments.

    >char ans;
    Despite the name, getchar actually returns an int so that it can properly handle EOF.

    >what am I not doing correct?
    I don't know. What input are you giving the program and what did you expect to happen?
    My best code is written with the delete key.

  3. #3
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    reply

    what I like to do is to have one user input. and if that user input is the condition used with the while loop the loop should be run else not. then when the loop is almost finished (in the end of the loop) have another user input to ask to repeat the same thing (the same loop)

    (the example program is just to make it simple)

  4. #4
    Its hard... But im here swgh's Avatar
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    So you basicly want somthing like this:

    Code:
    printf("Enter a number: ");
    scanf("%d", &num);
    
    while ( num != 100 )
    {
       printf("No, give me a ton: ");
       scanf("%d", &num);
    }
    That may not ne what you want, but its along the same lines
    I'm just trying to be a better person - My Name Is Earl

  5. #5
    Registered User ssharish2005's Avatar
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    Code:
    #include <stdio.h>
    
    void clear_buffer(void)
    {
        int ch;
        
        while((ch=getchar()) != '\n' && ch != EOF);
    }
    
    int main()
    {
       int ans;
       
       while((ans=getchar()) != 'd')
       {
         printf("sum\n");
         clear_buffer();
       }   
       
       getchar();
       return 0;
    }
    hope this will solve the problem

    sshaish2005

  6. #6
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    hi,

    you got to understand one thing here, getchar accepts a character from the standard input device .i.e. keyboard, when u press a character it is stored in 'ans' first, then you press enter key which is also a character again.
    This is what lets your program print the statement twice, to rectify this you need not change your whole program like other people suggested, but just add a line in your present program saying ' fflush(stdin); ' immediately after the getchar() line.
    This will solve your problem.

  7. #7
    CSharpener vart's Avatar
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    program saying ' fflush(stdin);
    Why fflush(stdin) is wrong
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  8. #8
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    Hi vart,
    I mean the program should be something like this
    Code:
    void main()
    {
    char ans;
    ans=getchar();
    fflush(stdin);
    while (ans!='d')
    {
    printf("sum\n");
    ans=getchar();
    fflush(stdin);
    }
    }
    Vart, actually fflush() refreshs the buffer so, the problem will not persist.
    Am I wrong Vart?

    }

  9. #9
    CSharpener vart's Avatar
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    on some systems it will work, on some - will not...
    so - the FAQ provides a portable way to fflush input stream:
    FAQ > How do I... (Level 2) > Flush the input buffer
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  10. #10
    Registered User
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    hey all. thank you for many replies.

    SWGH: your answer works using an int variable, but not using a char variable

    ssharish2005 and vart: your answers works just fine. thank you

    dh

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