Thread: Why does program jump over first data input line?

Code:

#include <stdio.h>
#include<string.h>
#include<windows.h>

void menu (void);
void locate(short x, short y);
//void removeScrollbars(void);
void enterBill(void);

struct A
    {
        char bill[6];
        char date[10];
        char descr[36];
        char euros[9];
        char code[6];
    };

int main(void)
{
    //removeScrollbars();
    menu();

}

void menu(void)
{
    system("@cls||clear");
    char s;
    locate(5,5); printf("1 = Enter a bill");
    locate(5,6); printf("2 = Retrieve a bill");
    locate(5,7); printf("3 = Correct a bill");
    locate(5,8); printf("4 = Enter a description");
    locate(5,9); printf("5 = Change a description");
    locate(5,11); printf("Make a selection: ");
    s = getchar();
    if (s == '1') enterBill(); else exit(0);
}

void enterBill(void)
{
    system("@cls||clear");
    struct A B;

    strcpy(B.bill,"");
    strcpy(B.date,"");
    strcpy(B.descr,"");
    strcpy(B.euros,"");
    strcpy(B.code,"");

    // This entry line is being passed over

    char *p;
    locate(5,5);printf("Bill numer");locate(30,5);printf(": ");
    fgets(B.bill, sizeof(B.bill),stdin);    
    if( (p = strchr(B.bill,'\n')) != NULL ) *p = '\0';
        
    locate(5,6);printf("Enter date");locate(30,6); printf(": ");
    fgets(B.date, sizeof(B.date),stdin);                         
    if( (p = strchr(B.date,'\n')) != NULL ) *p = '\0';

    locate(5,7);printf("Amount");locate(30,7);printf(": ");
    fgets(B.euros, sizeof(B.euros),stdin);                
    if ( (p = strchr(B.euros,'\n')) != NULL ) *p = '\0';

    locate(5,8);printf("Code");locate(30,8);printf(": ");
    fgets(B.code, sizeof(B.code),stdin);
    if ( (p = strchr(B.code,'\n')) != NULL ) *p = '\0';


    FILE *C;
    C = fopen("data2","ab");
    fwrite(&B,sizeof(struct A),1,C);
    fclose(C);            

}

void locate(short x, short y) 
{
    COORD pos = {x, y};
    SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), pos);
}

Above is a test program to find out why the program jumps over the first entry line when you select 1 in the menu. I am showing a lot of code hoping my question will be clear. Please help. Many thanks, Zach.

Probably because you left a new line character in the input buffer inside the menu() function.

Originally Posted by jimblumberg

Probably because you left a new line character in the input buffer inside the menu() function.

Yes I assumed there was something left in a buffer; the question of course is where is what getting stuck, and how can I get rid of it. I have been trying everything I could think of for many hours, but in vain. I have given a lot of code, so one of you clever guys could put your finger on it )

Well the problem occurs because of the getchar() on line 36, and the problem is "seen" on line 55. The problem is that getchar() leaves the newline character in the input buffer, check the boards FAQ there are a couple of entries about this "problem"

How do I avoid a "dangling" newline when reading single character user input?

and

Flush the input buffer

Originally Posted by jimblumberg

Well the problem occurs because of the getchar() on line 36, and the problem is "seen" on line 55. The problem is that getchar() leaves the newline character in the input buffer, check the boards FAQ there are a couple of entries about this "problem"

How do I avoid a "dangling" newline when reading single character user input?

and

Flush the input buffer

The first quote uses scanf, which I don't in my test code because I was told not to because of its hicks and tricks.

The second code

Code:

#include <stdio.h> 

int main(void)
{
 // int   ch;
 // char  buf[BUFSIZ];
   
 // while ((ch = getchar()) != '\n');
 
 printf ("Enter some text: ");
  
  if (fgets(buf, sizeof(buf), stdin))
  {
    printf ("You entered: %s", buf);
  }
  
  return 0;
}

The last three lines only make sense to my C-rooky brain.

Jim, first of all as I was told, don't use scanf, secondly, the golden code line seems to be:

Code:

    //s = getchar();
    while ( getchar() != '\n' );
    // use s

Well if that suffices, that is not so bad then.
Although I think a mature language shouldn't need such plasters.
Thank you for your help! Zach k.

Originally Posted by zach

Jim, first of all as I was told, don't use scanf, secondly, the golden code line seems to be:

Code:

    //s = getchar();
    while ( getchar() != '\n' );
    // use s

Well if that suffices, that is not so bad then.
Although I think a mature language shouldn't need such plasters.
Thank you for your help! Zach k.

The better version of the code is:

Code:

   int ch = 0;
   while ((ch = getchar()) != '\n' && ch != EOF);

Simple enough to create a function to call in multiple places. This will work if the input is from the keyboard, from a file, or when using redirection from a file on the command line.

Your first quote is about scanf, which I was previously told to avoid because of its hicks and tricks.

It cannot surely be true that you have to add lines of code to compense for the C language dysfunctioning!!

So, Jim, C is a language of which you cannot simply use the data input functions, because you will end up in a hell of a mess? Zach. K

Originally Posted by laserlight

The problem with scanf is basically the same problem you have with using getchar to read a char: it leaves the newline from entering the input in the input buffer, which doesn't play well with fgets and other line-based input functions. If you want to avoid scanf because of this, then avoid getchar as well: always use fgets or other line-based input functions to read the entire line of input, then parse the line for what you want, possibly with sscanf (but other functions are available too, e.g., strtol, or if you just want a char, you can easily manually parse the line for that char).

Thank you! I will have to chew over what you say. I still have much to learn. I am making a reference manual for myself as I go along and learn from my needs , mistakes and responses like yours. Zach.

Hi Laserlight, at this point in time I have been messing about for a few days apparently because of stuff dangling about in the buffer. If I manage to overcome the problem at one point in the program, a new bug arises elsewhere. It is truly disheartening. Surely other people will have set up a menu driven application before and have encountered the wall I seem to be up against. Is it is impossible to write a menu driven program in C? In the past I have written in other languages and have never experienced bugs in the language like the ones I am up against now.

Originally Posted by zach

Is it is impossible to write a menu driven program in C?

Do you believe if I tell you it is possible to write entire opeating systems and GUIs in C?