How to use Files in your programs
=================================

Note 1: The problem to be solved is:
======

(From Prac Test 4, Q10). Write a program that reads in from the first line
an integer n, and thereafter on n subsequent lines two things per line
(an int SSN and a float wages-earned). All this is from a file.
You must prompt for the filename as a string that is certain to be 
less than 30 chars long.
Open the file, etc., read everything, and keep a running total of all 
the wages earned, then when reading is complete, prompt for an output
filename string, open it and write to it the average value of all the
earnings.



Note 2: We will divide the problem into TWO steps: the step of solving the 
======  problem without files (simple program without files) and the step
        of adding files. We refer to the first step as the Baby or Logic step.

The solution to the "Baby" stage, or "Logic" stage is:

   The starting program


   #include <stdio.h>
   int main() {
   
     int n;
     int ssn; float wages, wagestotal=0;
     scanf("%d", &n);
     for(i=0;i<n;i++)
      {  scanf("%d%f", &ssn, &wages);
         wagestotal += wages;
      }
         
     printf("%f", wagestotal/n);
      
   return 0;
   }



Note 3: Begin Step 2: Changes that are needed to do Files (for reading)
======

   Changes needed to do (reading) files:


   FILE  *fp1;


   fp1 = fopen("inputfile1.txt", "r");


   fscanf(fp1, ...



   fclose(fp1);



Note 4: Continue Step 2: Changes that are needed to do Files (for writing)
======

   Changes needed to do (writing) files:


   FILE  *fp2;


   fp2 = fopen("outputfile1.txt", "w");


   fprintf(fp2, ...



   fclose(fp2);



Note 5: (All Step 2)Changes that are needed to do Reading and Writing of files:
======

   Changes needed for reading and writing files:


   FILE  *fp1;
   FILE  *fp2;


   fp1 = fopen(word, "r");
   fp2 = fopen("outputfile1.txt", "w");


   fscanf(fp1, ...

   later, do, as needed,
      fprintf(fp2, ...


   fclose(fp1);
   fclose(fp2);


Note 6: Final Program:
======

   #include <stdio.h>
   int main() {
   FILE*  fp1;
   FILE*  fp2;
     int n,i;
     int ssn; float wages, wagestotal=0;
     char word[30],word2[30];
     printf("type input fname:");
     scanf("%s",word);
     printf("type output fname:");
     scanf("%s",word2);

     fp1 = fopen(word, "r");
     fp2 = fopen(word2,"w");

     fscanf(fp1,"%d", &n);
     for(i=0;i<n;i++)
      {  fscanf(fp1,"%d%f", &ssn, &wages);
         wagestotal += wages;
      }
         
     fprintf(fp2,"%f", wagestotal/n);
      
   fclose(fp1);
   fclose(fp2);
   return 0;
   }