Thread: Adding records to a 2 dimensional database.

  1. 01-16-2005 #1
    colinuk
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    Adding records to a 2 dimensional database.

    Hi Guys,

    Im working on an exersiz that requires the user input a name , 4 scores and an ID number for the record being added.

    I had it all going but when I try to add the ID numbers taken from the user and do a check to see if the number is taken ive got a little lost.....

    I wonder if anyone can point out the flaws in my function below?

    Regards as ever
    Colin

    Code:
    void add_new_name(void)

{

int found=0;
int record_id;
int loop=0;
clrscr();

/* Add the name and DOB & ID to the database*/

printf("\n\n\t\t   Enter new name and Grades\n\n");
printf("Enter new name: ");
gets(names_database[index].name);
flush(stdin);

printf("Please enter 4 grade marks in as a percentage value:\n\n");
scanf("%d%d%d%d",&names_database[index].grade1, &names_database[index].grade2,&names_database[index].grade3,&names_database[index].grade4);
fflush(stdin);

printf("Please enter an ID number between 100-999\n");
scanf("%d",&record_id);
fflush(stdin);


while(found=0 && loop < MAX)
{

 if(record_id == names_database[loop].id)

{
printf("This ID number is taken");
printf("Please Re-enter an ID number between 100-999\n");
scanf("%d",&record_id);
fflush(stdin);
}

loop++;

}

if(found=0)
{
names_database[loop].id = record_id;
}

/* Increment the student array */
index++;

}
  2. 01-16-2005 #2
    Sebastiani
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    >> gets(names_database[index].name);
    >> flush(stdin);

    1) don't use gets() - use fgets() to prevent buffer overflow.
    2) fflush() is not intended for input streams - read the FAQ for more reliable ways to do that.
    3) what happens when you enter the function and index > MAX?


    >> while(found=0 && loop < MAX)

    I don't see where 'found' is actually used, but at any rate, you're setting it - not testing it - with the value of zero each iteration. and there's no sense in testing data from 'index' through 'MAX' since there isn't any valid data there anyway.

    >> if(found=0)

    again, this should be ==.

    >> if(record_id == names_database[loop].id)

    what happens if the new 'record_id' corresponds to a value already passed in previous iterations of the loop? for instance, let's say the first 4 id's are:

    98
    21
    72
    35

    suppose the user chooses '72'. when you find that value at position three you prompt for a new number and the user chooses '98' - since you didn't restart loop you'll never know that number is already taken, too.

    >> names_database[loop].id = record_id;

    'loop' is going to be MAX - 1, what you want is the element at 'index'.
    Code:
    #include <cmath>
#include <complex>
bool euler_flip(bool value)
{
    return std::pow
    (
        std::complex<float>(std::exp(1.0)), 
        std::complex<float>(0, 1) 
        * std::complex<float>(std::atan(1.0)
        *(1 << (value + 2)))
    ).real() < 0;
}
  3. 01-16-2005 #3
    colinuk
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    Hi Sebastiani

    Thanks for your reply,

    Im still a little stuck, forgive me Im a newbie to C.....

    Im sure its my loop thats wrong but I cant puzzle it out as yet.

    Here is what I tried after your suggestion, I cant think how to recheck the ID once its has been entered again??

    Perhaps you couls assist me again.

    Thanks again

    Code:
    while(found==0 && loop < MAX)  /*Max is defined as 999*/
{

if(record_id == names_database[loop].id)

{
found=1;
printf("This ID number is taken");
printf("Please Re-enter an ID number between 100-999\n");
scanf("%d",&record_id);
fflush(stdin);
}

loop++;

}

if(found==0)
{
names_database[loop].id = record_id;
}

/* Increment the student array */
index++;
  4. 01-16-2005 #4
    Sebastiani
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    something like:

    Code:
     int retry = 1; 
 while(retry) 
 {
  retry = 0; 
  loop = 0;
  while(loop < index)  
  {
   if(record_id == names_database[loop].id)
   {
    printf("This ID number is taken");
    printf("Please Re-enter an ID number between 100-999\n");
    scanf("%d",&record_id);
    fflush(stdin);
    retry = 1;
    break; 
   }
  loop++;
  }
 }
    >> names_database[loop].id = record_id;

    again, you're not assigning the id to the proper array element.
    Code:
    #include <cmath>
#include <complex>
bool euler_flip(bool value)
{
    return std::pow
    (
        std::complex<float>(std::exp(1.0)), 
        std::complex<float>(0, 1) 
        * std::complex<float>(std::atan(1.0)
        *(1 << (value + 2)))
    ).real() < 0;
}
  5. 01-16-2005 #5
    colinuk
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    Hi there,
    Thanks for your quick reply,

    Can you tell me what "while(retry)" means??

    Thanks again
  6. 01-16-2005 #6
    Kybo_Ren
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    It is a variable that is set to 1 when the user has to enter the data.

    That way the user will keep getting that message and have to enter the data until they enter valid input.
  7. 01-16-2005 #7
    Sebastiani
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    conditionals always evaluate the non-zero-ness of a condition. so:

    while(retry)

    is semantically the same as:

    while(retry != 0)
    Code:
    #include <cmath>
#include <complex>
bool euler_flip(bool value)
{
    return std::pow
    (
        std::complex<float>(std::exp(1.0)), 
        std::complex<float>(0, 1) 
        * std::complex<float>(std::atan(1.0)
        *(1 << (value + 2)))
    ).real() < 0;
}
  8. 01-16-2005 #8
    colinuk
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    Thanks Guys,

    I will see how I get on....Your comments are very appreciated.

    Regards as ever.
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