Need some help doing error checking

**t_6** · 05-27-2008

Hi everybody,

I am in an introduction to C class and here is a program we had to do. Now, what I am trying to do is expand on it a little more and do some error checking. So, if the user inputs something other than the correct amount or the correct store I want it to loop back up and ask again. Can someone help, I have tried using a for loop but I haven't been able to get it to work correctly.

Code:

#include <stdio.h>

// function prototypes 
float tax_delmar(float);
float tax_encinitas(float);
float tax_lajolla(float);
float add_total(float, float);

// global variables that can be used by any function
float sales_tax;
float total;


main()

{

	//defining and initializing data type 
	float purchase_amt = 0.0;
	char  store = '0';
	
	
	printf("\nWhat is your purchase amount? $");
	//receiving user input for the purchase amount
	scanf("%f", &purchase_amt);
	
	printf("\nWhat store?\n");
	printf("\nPress D for DelMar, E for Encinitas, or L for LaJolla: ");
	scanf("%c", &store);

	
	if(purchase_amt >= 0.0 && purchase_amt <= 1000.0 && store == 'd')
	{
	//sales tax for the Del Mar store rate
	printf("\n\nSales tax for $%.2f at the DelMar store is: $%.2f\n", purchase_amt, tax_delmar(purchase_amt));
	//total price with sales tax included for the Del Mar store
	printf("\nThe total purchase price at the DelMar store is = $%.2f\n\n\n", add_total(sales_tax, purchase_amt));
	}
	else if(purchase_amt >= 0.0 && purchase_amt <= 1000.0 && store == 'e')
	{
	//sales tax for the Encinitas store rate
	printf("\nSales tax for $%.2f at the Encinitas store is: $%.2f\n", purchase_amt, tax_encinitas(purchase_amt));
	//total price with sales tax included for the Encinitas store
	printf("\nThe total purchase price at the Encinitas store is = $%.2f\n\n\n", add_total(sales_tax, purchase_amt));
	}
	else if(purchase_amt >= 0.0 && purchase_amt <= 1000.0 && store == 'l')
	{
	//sales tax for the La Jolla store rate
	printf("\nSales tax for $%.2f at the LaJolla store is: $%.2f\n", purchase_amt, tax_lajolla(purchase_amt));
	//total price with sales tax included for the La Jolla store
	printf("\nThe total purchase price at the LaJolla store is = $%.2f\n\n\n", add_total(sales_tax, purchase_amt));
	}
	
	printf("\nPress return to end program!\n");
	
	//pausing program until user ends program
	getch();
	return;
	
}	

//calculate the sales tax on the purchase amount for the Del Mar store	
float tax_delmar(float purchase_amt) 
{
	sales_tax = purchase_amt * 0.0725;
	return sales_tax;
}
//calculate the sales tax on the purchase amount for the Encinitas store
float tax_encinitas(float purchase_amt) 
{
	sales_tax = purchase_amt * 0.075;
	return sales_tax;
}
//calculate the sales tax on the purchase amount for the La Jolla store	
float tax_lajolla(float purchase_amt) 
{
	sales_tax = purchase_amt * 0.0775;
	return sales_tax;
}
//add up a total for the purchase amount plus the sales tax for that amount
float add_total(float sales_tax, float purchase_amt)
{
	total = sales_tax + purchase_amt;
	return total;
}

**jason_m** · 05-27-2008

Your choice for loops are:
for, while, and do

I'll do the easier comparison first, while and do.
A while looks like

Code:

while (condition) {
  statement(s);
}

So, if condition isn't true to begin with, the loop will never be executed.

A do loop looks like

Code:

do {
  statement(s);
} while (condtion);

So the statement(s) in the body of a do loop with always be executed at least once. If you want to read in some input and loop until it satisfies some criteria, you may often want a do loop.

The for loop looks something like:

Code:

for(statement1, condition, statement2) {
  statement(s);
}

and is the same as (stealing from K&R)

Code:

statement1;
while (condition) {
  statement(s);
  statement2;
}

So, a for is just a special kind of while loop. The context of the problem usually indicated which is better.

Hope that helps some.

**Elysia** · 05-28-2008

Don't forget that scanf will leave stuff in the input buffer if the user enters incorrect information.
Therefore, the easiest approach to this problem is typically to read a string, then convert to appropriate data type and check if the conversion succeeds. If it doesn't, then it's a bad input.
String to float -> strtof.
And for the char, just grab the first character in the string you read.
For reading strings, use fgets.

**rags_to_riches** · 05-28-2008

University of Phoenix assignment? Seems I've seen this before...

**t_6** · 05-29-2008

Thanks everybody! Yes, it's for UOP.

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