reading a complex txt file

[EDIT: 20110620 14:20 CDT - reformat - WDR]

I want to read a text file as below and use it in an iterative manner, after reading and making some changes I need to write it as a text file and then use it for the next iteration, the file consists of 6 sections, that I copied a couple of lines for each section below. I appreciate it if someone can help me with this.

the 1st section is just one line showing 1,

the 2nd section is again one line showing 0.00. these two sections are always the same.

the 3rd section always contains 5388 lines with 4 fields (always 4 fields).

number of lines in the 4th section is not fixed but can be found: the number of lines in the 4th section can be found from the elements with values of 4 or 5 in the 2nd field of the 3rd section PLUS some additional lines for each, in other words, each 4 or 5 (from section 3-field 2) forms a couple of 10-field line in section 4 (always 10) the number of generated 10-field lines equals the value of the 3rd field of the corresponding 4-field line in the 3rd section, and about additional lines, the 6th field of the 10-field lines shows the number of additional lines that are added right after the 10-field lines, these additional lanes can have different numbers of fields from min:5 to max:8 (the exact number of fields can be found from the 4th field of the additional lines),

the 5th section is just one line of string data,

the 6th section is somehow similar to section 4: the number of lines in this section equals the total number of elements with values of 6 in the 2nd field of the 3rd section PLUS some additional lines for each, in other words, each 6 (from section 3-field 2) forms a 3-field line in section 6 (always 3 fields), and about additional lines, for each 3-field line, 2 lines are added (always 2), the number of fields of the first added line equals 2*(the value of the 2nd field in the corresponding 3-field line), and the number of fields of the second added line equals 2*(the value of the 3rd field in the corresponding 3-field line),

here is a better sample: (the 1st field of the 3rd section (1,6,75,5075,5214) shows IDs so they can be traced in the sections 4 and 6)

1
    0.00
    1 5 4 180
    6 1 0   0
   75 6 0   0
 5075 4 4 105
 5214 6 0   0
    1      1     32      5      4      1      4      0      0      0
    4      1      1      3   7062   6493  16015
    1      2     32      5      4      1   6493      0      0      0
 6493      1      2      3  16015      4   7062
    1      3     32      5      4      1   7062      0      0      0
 7062      1      3      3   6493  16015      4
    1      4     64      5      4      1  16015      0      0      0
 5075      1     76     10      7      2   5077   6060      0      0
 5077   5075      1      2   6059   5074
 6060   5075      1      2   5074   6059
 5075      2     76     32      7      2   5077   6060      0      0
 5077   5075      2      2   6060   5074
 6060   5075      2      2   5077   6059
 5075      3     76     25      7      1   5074      0      0      0
 5074   5075      3      3   5077   6059   6060
 5075      4     76     10      7      1   6059      0      0      0
 6059   5075      4      3   6060   5074   5077
=======Two Way Stop Signs/Yield Signs Below =======
   75      2      2
  750     75   6186     75
   76     75   6182     75
 5214      2      3
 5237   5214   5255   5214
  440   5214   5224   5214   5258   5214

I want to change some values in the 3rd section that consequently will change some parts of the data in the 4th and 6th sections, and finally I want to write this file in the same format, then again from the beginning so I’d like to use this file in an iterative process, at each iteration I need to read the file and after some modifications, write it for the next iteration.

[Walter Roberson]

I am not sure why you do not read the file in, perform _all_ of the iterations, and then write it out only once?