gets function

This is a discussion on gets function within the C Programming forums, part of the General Programming Boards category; I am haing a problem with the loop in my code. It works fine until the second iteration through the ...

  1. #1
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    gets function

    I am haing a problem with the loop in my code.
    It works fine until the second iteration through the loop.
    When I make the loop into the code:

    printf("Please enter the first word\n");

    gets(str1);
    printf("%s a\n", str1);

    count1 = strlen(str1);

    printf("Please enter the second word\n");

    gets(str2);
    printf("%s a\n", str2);
    count2 = strlen(str2);
    The code appears to pass right by the first printf() and gets(str1)
    and goes directly to str2 printf() and gets.

    What is causing this problem?

    The first time into the loop it works correctly.

  2. #2
    Registered User Sargnagel's Avatar
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    I guess it's because there is a '\n' left in the stdin stream after reading in the first string.
    You just have to flush stdin with this or a similar function before gets(str2) is called:
    Code:
    void tidy (FILE *in)
    {
        int c;
        while( (c = fgetc(in)) != EOF && c != '\n');
    }
    You can not write the following:

    fflush(stdin);

    This is undefined by the ANSI C99 Standard!

  3. #3
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    I had added printf() to do some debugging. This is what I have without the debug printf().
    here is the whole code:
    #include <stdio.h>
    #include <string.h>
    #include <ctype.h>
    #define str_length 100
    void main()
    {

    char str1[100];
    char str2[100];
    int count1;
    int count2;
    char more ; /* variable to continue with the loop y||Y */




    do
    {

    printf("Please enter the first word:");

    gets(str1);


    count1 = strlen(str1);

    printf("Please enter the second word:");

    gets(str2);

    count2 = strlen(str2);


    /* concatenate str2 to end of str1 */
    if(count1 == count2 ||count1 < count2 )
    {
    printf(" %s %s and \n", str1,str2);

    printf(" %s %s\n",strrev(str1), str2);

    }
    else
    /* concatenate str1 to end of str2 */
    {
    printf(" %s %s and \n", str2,str1);

    printf(" %s %s \n",strrev(str2),str1);

    }

    printf(" Would you like to continue? y or n:\n");
    scanf("%c", &more);


    }while(more == 'y' || more == 'Y');




    }

  4. #4
    Registered User Vber's Avatar
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    What is causing the problem? few things on your code.
    ->void main()
    The main function return's an integer, so change it to int main() and return an value at the end of main().

    ->gets(str2);
    Don't use gets(), search on the board about it, use instead fgets()
    http://man.he.net/man3/fgets

  5. #5
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    It still doesnt work.

  6. #6
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    #include <stdio.h>
    #include <string.h>
    #include <ctype.h>
    #define str_length 100
    int main()
    {

    char str1[100];
    char str2[100];
    int count1;
    int count2;
    char more ; /* variable to continue with the loop y||Y */




    do
    {

    printf("Please enter the first word\n");

    fgets(str1);
    printf("%s a\n", str1);

    count1 = strlen(str1);

    printf("Please enter the second word\n");

    fgets(str2);
    printf("%s a\n", str2);
    count2 = strlen(str2);


    /* concatenate str2 to end of str1 */
    if(count1 == count2 ||count1 < count2 )
    {
    printf(" %s %s and \n", str1,str2);

    printf(" %s %s\n",strrev(str1), str2);

    }
    else
    /* concatenate str1 to end of str2 */
    {
    printf(" %s %s and \n", str2,str1);

    printf(" %s %s \n",strrev(str2),str1);

    }

    printf(" Would you like to continue? y1 or n:\n");
    scanf("%c", &more);


    }while(more == 'y' || more == 'Y');

    return 0;


    }

  7. #7
    Me want cookie! Monster's Avatar
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    It's because you use the scanf function. This function has the nasty habbit to leave newline characters in your input buffer.
    You can try to flush your input buffer with the following line:
    Code:
    scanf("%c", &more); 
    while(getchar() != '\n') ; /* flush input buffer */
    For more information: FAQ

  8. #8
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    That was it! It worked. Thanks. The information on the scanf leaving a newline character is interesting. Does this always occur in a scanf() or is it intermitent?

  9. #9
    Me want cookie! Monster's Avatar
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    >> Does this always occur in a scanf() or is it intermitent?

    For normal use with the scanf function: Yes

    This is one of the reasons I always use the fgets function to read from input and for example the sscanf function scan the buffer.

    There are however some tricks you can use with the scanf function so prevent the function from leaving the newline character in the input buffer.

  10. #10
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    Cool. Thanks for the help, the info. and the links.

  11. #11
    Me want cookie! Monster's Avatar
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    You're welcome.

    b.t.w. take a look at Salem's advice

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