how to do do line by line comparison of data of 2 files if if open files in binary in c?

Question

the question :- In the file 'CUSTOMER.DAT' there are 100 records with the structure customer .In another file 'TRANSACTIONS.DAT' there are several records with the structure trans

The element trans_type contains D/W indicating deposit or withdrawal of amount. Write a program to update 'CUSTOMER.DAT' file, ie, if the trans_type is 'D' then update the balance of 'CUSTOMER.DAT' by adding amount to balance for the corresponding accno. Similarly, if trans_type is 'W' then subtract the amount from balance.

I am able to compare line by line data in a file if i open file in txt mode ie in "r" and "w" but when i open in binary "rb" "wb" ,i can't compare line by line data. How to do it?

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>

struct customer
{
  int accno ;
  char name[30] ;
  float balance ;
};

struct trans
{
  int accnum ;
  char trans_type ;
  float amount ;
} ;


int main()
{
    FILE *fs,*ft,*f1;

    struct customer c;
    struct trans tr;

    fs = fopen("customer.txt","rb");

    if (fs==NULL)
    {
        printf("Can't open file.");
        exit(1);
    }

    f1 = fopen("transactions.txt","rb");

    if (f1==NULL)
    {
        printf("Can't open file.");
        exit(2);
    }


    ft = fopen("temp.txt","wb");

    if (ft==NULL)
    {
        printf("Can't open file.");
        exit(3);
    }

    while(fread(&c,sizeof(c),1,fs)==1)
    {
        while(fread(&tr,sizeof(tr),1,f1)==1)
        {
            if( tr.accnum == c.accno && tr.trans_type == 'D')
            {
                c.balance = c.balance + tr.amount;
                break;
            }

            else if( tr.accnum == c.accno && tr.trans_type == 'W')
            {
                if(c.balance - tr.amount < 100)
                    break;
                else
                    c.balance = c.balance - tr.amount;

                break;
            }
        }
        fwrite(&c,sizeof(c),1,ft);
    }
    fclose(fs);
    fclose(f1);
    fclose(ft);

    remove("customer.txt");
    rename("temp.txt","customer.txt");
    return 0;

}

The data sample in customer.txt is

1 aman 456.45

2 loma 199.40

3 shail 15

The data sample in transactions.txt is

1 D 500.89

3 W 51.00

2 W 40

where D is deposit and w is withdraw

Answer 1

File data is encoded as text . Do not read the data with fread() which expects a fixed length binary data.

Open the file in text mode and read the line of data with fgets() .

char buffer[100];
if (fgets(buffer, sizeof buffer, fs)) {
  // Now process the data

Let us process the data with sscanf() . Look for malformed data. Use " %n" to record the offset of trailing non-white-space text.

  struct trans tr;
  int n = 0; 
  sscanf(buffer, "%d %c %f %n", &tr.accnum, &tr.trans_type, &tr.amount, &n);
  // Was scanning incomplete or extra junk at the end or non W,D?
  if (n == 0 || buffer[n] != 0 || 
      (tr.trans_type != 'W' && tr.trans_type != 'D')) {
    fprintf(stderr, "Bad input <%s>\n", buffer);
    break;
  }

  // Use `t`. 

}

When it is time to write, use sufficient precision to write a distinctive float .

 fpritnf(fs, "%d %c %.9g\n", t.accnum, t.trans_type, t.amount);