reading from text file to find average number

[kw1991]

i have a text file with 30 records of dates and numbers(rainfall)
i want to find the average rainfall between two dates so i want to be able to enter two dates and the output will give me the average rainfall of those two dates

a record will look like this:
1 12 2009 2.5
2 12 2009 5.1
and so on til 30

heres what i have so far. all this code does so far is display the date

int day = 0, month = 0, year = 0;
cout <<"Enter a date : " << endl;
cin >> day,month,year;
for (int i = 0; i < 30; i++)
{
if (day, month, year == date[i].day, date[i].month, date[i].year) 
{
infile >> date[i].day >> date[i].month >> date[i].year >> report[i].rainfall; 

cout << "rainfall for the "<< date[i].day << "/" << date[i].month << "/" << date[i].year << " is " << report[i].rainfall  << endl;
					}
				 }

i havn't got the average yet because i want to make sure the correct date is displaying which its not. The output is displaying all dates instead of the date i entered

[kw1991]

really hope someone can help me with this
thanks

[JMJAtlanta]

take a look at how to build an "if" statement.

	if (day, month, year == date[i].day, date[i].month, date[i].year) 

should be expressed

	if (day == date[i].day && month == date[i].month && year == date[i].year) 

[kw1991]

ok but now its not displaying anything
i want to display the date i just entered

[Mathhead200]

Line 3...

[kw1991]

ok but what do i do? if i remove line 3 it still doesnt display anything

[Gaminic]

The "comma operator" doesn't work that way. Not in an if, not in a cin. For a cin, repeat the >> ('in' operator) for each variable.

[kw1991]

ok thanks it works so now the code looks like this:

int day = 0; 
int month = 0; 
int year = 0;
cout <<"Enter a date : " << endl;
cin >> day >> month >> year;

for (int i = 0; i < 30; i++)
{
	if (day == date[i].day && month == date[i].month && year == date[i].year) 
	{
	infile >> date[i].day >> date[i].month >> date[i].year >> report[i].rainfall; 
	cout << "rainfall for the "<< date[i].day << "/" << date[i].month << "/" << date[i].year << " is " << report[i].rainfall  << endl;
	}
 }

int day2 = 0; 
int month2 = 0; 
int year2 = 0;
cout <<"Enter another date : " << endl;
cin >> day2 >> month2 >> year2;

for (int i = 0; i < 30; i++)
{
	if (day2 == date[i].day && month2 == date[i].month && year2 == date[i].year) 
	{
	infile >> date[i].day >> date[i].month >> date[i].year >> report[i].rainfall;
	cout << "rainfall for the "<< date[i].day << "/" << date[i].month << "/" << date[i].year << " is " << report[i].rainfall  << endl;
}

now i want to be able to take the two rainfall numbers that displayed and find the average of them

[Gaminic]

You're already accessing the data in your ifs. Now just save them in a variable. Make sure to declare the variable outside of the for loops, because you'll need them afterwards.

You can either use N variables to store all N rainfalls (N = 2 in your question, but in the general case where you want multiple days, you'll need N variables) and then sum and divide at the end, or use one variable to store the total. In the first case, you'll need a separate variable for each and use the assignment operator ('=') inside the ifs. The latter case needs one variable (initialize at 0!) and the addition operator ('+=').

[kw1991]

ok so do you mean something like this?

  int N = 0; 
double average;
average = (report[N].rainfall + report[N].rainfall)/2;
cout << "Average rainfall is : " << average << endl;
 

i know this code is wrong though because the average output is not correct
could you tell me what i'm doing work?

[kw1991]

can anyone help with this?

[Mathhead200]

No...

double sum = 0; //a running total
for( int i = 0; i < N; i++ ) //loop though the "report" array, where "N" is it's length
    sum += report[i].rainfall; //add to the running total
double avg = sum / N; //calculate the average 

report[N] would be outside the array's boundaries. Array indexes must be an integer in [0, N) i.e. [0, N-1].

[kw1991]

its still not working

int N =0;
double sum = 0; 
for( int i = 0; i < N; i++ )
sum += report[N].rainfall; 
double avg = sum / N; 
				
cout << "avgerage = " << avg << endl;

the output looks like this

Enter a date: 12 12 2009
rainfall on the 12 12 2009 is 1.8
Enter another date:13 12 2009
rainfall on the 13 12 2009 is 2.3
average = -1.#IND

it should be getting the average of 1.8 and 2.3 but now its not even display a number

[ne555]

Think in what you are doing. Use pen and paper to follow your program.

[Mathhead200]

report[i], iterate through the array by increasing i each time... Not array[N] which tries to dereference memory that is out of bound!