Chapter - 13: File Input-Output

In the file ‘CUSTOMER.DAT’ there are 100 records with the following structure:


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

In another file ‘TRANSACTIONS.DAT’ there are several records with the following structure:

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

The parameter trans_type contains D/W indicating deposit or withdrawal of the amount. Write a program to update ‘CUSTOMER.DAT’ file, i.e. if the trans_type is ‘D’ then update the balance of ‘CUSTOMER.DAT’ by adding the amount to balance for the corresponding account. Similarly, if trans_type is ‘W’ then subtract the amount from balance. However, while subtracting the amount make sure that the amount should not get overdrawn, i.e. at least 100 Rs. Should remain in the account.


Ans:

#include<stdio.h>
#include<Windows.h>
#include<string.h>
#include<conio.h>

void display(char*);
void add_info(int, char*, float);
void transaction(int, char, float);

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

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

int main()
{
	add_info(1, "Siraj", 1000);
	puts("\n\t\tBefore Transaction");
	display("customer.dat");
	transaction(1, 'd', 1000);
	puts("\n\t\tAfter Transaction");
	display("customer.dat");
	_getch();
	return 0;
}

void display(char *file)
{
	FILE *fp;
	struct customer holder;
	fp = fopen(file, "rb");
	while (fread(&holder, sizeof(holder), 1, fp) == 1)
	{
		printf("\n%d", holder.accno);
		printf(":\t%s", holder.name);
		printf("\t%f\n", holder.balance);
	}
	fclose(fp);
}

void add_info(int accno, char *name, float bal)
{
	FILE *fp;
	struct customer holder;
	fp = fopen("customer.dat", "rb+");
	if (fp == NULL)
		fp = fopen("customer.dat", "wb");
	fseek(fp, 0, SEEK_END);
	holder.accno = accno;
	strcpy(holder.name, name);
	holder.balance = bal;
	fwrite(&holder, sizeof(holder), 1, fp);
	fclose(fp);
}

void transaction(int accno, char ttype, float amount)
{
	FILE *fp, *temp;
	struct customer holder;
	fp = fopen("customer.dat", "rb");
	temp = fopen("temp.dat", "wb");
	while (fread(&holder, sizeof(holder), 1, fp) == 1)
	{
		if (holder.accno == accno)
		{
			switch (ttype)
			{
			case 'd':
			case 'D':
				holder.balance += amount;
				break;
			case 'w':
			case 'W':
				if ((holder.balance - amount) < 100)
				{
					system("cls");
					printf("\nYour account balance is low.\n");
					printf("Transaction failed!!");
					_getch();
				}
				else
					holder.balance -= amount;
				break;
			default:
				system("cls");
				puts("Wrong transaction type!!");
				puts("\nTry Again!!");
				fclose(fp);
				fclose(temp);
				remove("temp.dat");
				return;
			}
		}
		fwrite(&holder, sizeof(holder), 1, temp);
	}
	fclose(fp);
	fclose(temp);
	remove("customer.dat");
	rename("temp.dat", "customer.dat");
}

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