Reading in only first couple lines of input file

[chara76]

I'm trying to create a program that reads in data for 3 separate days and analyzes it. The data file has 72 lines (24 for each day). I only want to read in data for the first day (first 24 lines), but I cannot figure out how to.
-------------------------------------------------------------------------------------------------------
#include <iostream> // Needed for normal cin & cout statements
#include <fstream> // Needed to read or write files on disk
#include <cstdlib> // Needed for exit
#include <cmath> // Needed for certain math functions
#include <string> // Needed to read strings
using namespace std;
int main()
{
// Initializes variables
double Data1, Data2, Data3, Total(0);
int k;

// Opens data file
ifstream infile;
infile.open("data.txt");

if(!infile)
{
cout<<"Unable to open file: Data.txt\n"; // Displays error message if data file cannot be opened
system("pause"); // Pauses command window
exit (0); // Exits program
}
else
{
for(k=1; k<=24; k++) //Counter to read first 24 lines
{
while(infile>>Data1>>Data2>>Data3) // Reads in 3 data items
{
if(Data1 > 1) // Ignores Data1 if it is 1 or 0
Total=Total+Data1; // Adds up Data1 for first 24 lines
}
}
cout<<Total<<endl;
}
system("pause"); //Pauses console window
return (0); // Ends program
}

[laserlight]

This:

while (infile >> Data1 >> Data2 >> Data3) // Reads in 3 data items
{
    if (Data1 > 1) // Ignores Data1 if it is 1 or 0
        Total = Total + Data1; // Adds up Data1 for first 24 lines
}

should be:

if (infile >> Data1 >> Data2 >> Data3) // Reads in 3 data items
{
    if (Data1 > 1) // Ignores Data1 if it is 1 or 0
        Total += Data1; // Adds up Data1 for first 24 lines
}
else
{
    // report missing data?
    break;
}

Notice that I posted in [code][/code] bbcode tags and indented the example code. Next time, please do the same.

EDIT:
Also, try and declare variables near first use. It is bad practice to declare Data1, Data2, Data3, Total and k at the start the main function when you could have declared them before the loop. In fact, you can even declare k in the for loop, i.e.,

for (int k = 0; k < 24; ++k)

Likewise, you could have declared Data1, Data2 and Data3 in the body of the for loop, though declaring them just before the loop is acceptable.

[chara76]

Thanks, that worked great. I'll make sure to post the right way next time.

[chara76]

How would I then read the data for the next day (lines 25-48)? I tried the following:

for(int k=1; k<=24; k++)
                   {
                   if(infile>>Data1>>Data2>>Data3)  // Reads in 3 data items
                        {                                             
                         if(sunlight > 1)  // Ignores Data 1 if it is 1 or 0
                             Total+=Data1;     // Adds up Data1 for first 24 lines                             
                        }
    
                   while(k>24 && k<=48)  // Analyzes data for lines 25 to 48
                         Total2=Data1;  // Adds up Data1 for lines 25 to 48
                   }

[davidk]

Use another loop, something like

for(int k=25; k<=48; k++)

Also, you have to add to 'total' variable, not overwrite its data.

Total2 += Data1;

[chara76]

Where would I add the new loop? I tried Adding it after the first for loop, but that did not work.

[davidk]

Basically, the same loop as first one, but change the variable 'Total' to 'Total2'.

Consider using arrays instead of variables like 'Total*' in case you wanna read next 3 days, or even more.

[chara76]

I'm still new to c++. Could you give an example of how to use an array?