How do you parse an input file to tell you which code to run?

The input file is structured as:

1 data + integer

1 data - integer

2 integer + data

3 data - data

4 data <= data

4 data == data

4 data > data

so that the the number on the front of each line tells you how to parse it. my code that specifically handles the input file is:

ifstream infile("test.txt");
int command = 0;
Data tempdata1, tempdata2;
int tempint = 0;
string s;
while(!infile.eof())
{
    infile >> command;        //should read the first int of each line            
                                    to determine how to handle the data
    switch(command)
    {
        case 1:
            infile >> tempdata1;
            infile >> s;
            infile >> tempint;

            /*handle the data and int according to if s is + or - */
            break;

        case 2:
            infile >> tempint;
            infile >> s;
            infile >> tempdata1;

            /*handle the data and int according to if s is + or - */
            break;

        case 3:
            infile >> tempdata1;
            infile >> s;
            infile >> tempdata2;

            /*handle the data and data according to if s is + or - */
            break;
        case 4:
            infile >> tempdata1;
            infile >> s;
            infile >> tempdata2;

            /*handle the data and data according to if s 
                is <=, <, ==, >=, or !=, etc */
            break;
    }

}

I have a class to handle these data types, with their operators overloaded. The code I have so far worked for the first 3 lines of my input file, but then it thought that 3 was 2 and treated it as a case 2. I also noticed that when I made the input file only 2 lines long, it looped through it 3 times.

My concise questions are:

1. 
   

   Is there a better way to parse this type of input file?

   
   


2. 
   

   Any ideas why the code mistreats some cases?