Unable to scan a character repeatedly

This is a discussion on Unable to scan a character repeatedly within the C Programming forums, part of the General Programming Boards category; Here's the code I wrote: Code: #include<stdio.h> #include<conio.h> void initialize(int array[9][9]) { int i = 0, j = 0; for(i ...

  1. #1
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    Unable to scan a character repeatedly

    Here's the code I wrote:

    Code:
    #include<stdio.h>
    #include<conio.h>
    void initialize(int array[9][9])
    {
         int i = 0, j = 0;
         for(i = 0; i < 9; i++)
         {
               for(j = 0; j < 9; j++)
               {
                     array[i][j] = 0;
               }
         }
    }
    void display(int array[9][9])
    {
         int i = 0, j = 0;
         for(i = 0; i < 9; i++)
         {
               for(j = 0; j < 9; j++)
               {
                     printf("%d   ", array[i][j]);
               }
               printf("\n");
         }
    } 
    int main(void)
    {
        int array[9][9];
        char c;
        initialize(array);
        display(array);
        printf("Enter the array elements: \n\n");
        while(1)
        {
                printf("\nWant to enter array element? ");
                scanf("%c", &c);
                if(c == 'y')
                {
                     printf("Accepted");
                     
                }
                else
                {
                    printf("Bye bye");
                    break;
                }
        }
        getch();
        return 0;
    }
    The scanf function works only once, it only scans the character once.
    On the second iteration, the scanf function is skipped and the loop exits.

    Am I do anything wrong?

    Thanks in advance.

  2. #2
    qny
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    Quote Originally Posted by Shyam Raj View Post
    Am I do anything wrong?
    Sort of ... you expect to press 2 keys, but the program to ignore one of them. It doesn't!
    Try printing the character you just read right after you read it in.

    Code:
                /* ... */
                scanf("%c", &c);
                printf("character read in: '%c' (value %d)\n", c, c);
                /* ... */

  3. #3
    and the hat of wrongness Salem's Avatar
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    When you've done with qny's suggestion and seen what is happening, you do this

    scanf(" %c", &c); //!! note the leading space in the format
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  4. #4
    SAMARAS std10093's Avatar
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    Also another irrelevant with scanf suggestion from me.
    Instead of having the prototype of the function like
    Code:
    void myFunction(int myArray[9][9])'
    i highly recommend you yo have it like this
    Code:
    void myFunction(int** myArray , int n);
    Why?
    Because in this way you make your function far more useable and re-usable in future programs, because know it will work for every size you want!

  5. #5
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    Hi qny, I understood what you said. Thanks for that.

    Salem, why is that we need to add a leading space? Why doesn't it work the way I tried?

  6. #6
    and the hat of wrongness Salem's Avatar
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    Instead of having the prototype of the function like
    void myFunction(int myArray[9][9])'

    i highly recommend you yo have it like this
    void myFunction(int** myArray , int n);
    This does NOT work.

    A true 2D array does not reduce to a **

    You can get to int (*array)[9], int n, so you can pass in any array[X][9]

    But there is no(*) way to pass any 2D array to a generic function.


    (*) Unless you resort to array flattening and manual subscript calculations.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  7. #7
    and the hat of wrongness Salem's Avatar
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    > Salem, why is that we need to add a leading space? Why doesn't it work the way I tried?
    A leading space causes scanf to discard any leading whitespace, such as the newline at the end of the previous input.
    This makes it behave like %s, %d, %f etc.

    %c (by itself) always takes the next character on the input stream (including any newlines left by previous scanf calls).
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  8. #8
    qny
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    scanf() was designed to deal with formatted data (reason for its name: scan_formatted).
    User input and formatted data are very very different.
    I suggest you use a function more capable of dealing with user input: fgets() and afterwards parse the input string for your needs (maybe with sscanf() or strtol() or ...)

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