Topics for today CISC105, 09/26/05
P. Conrad, Sections 022-025

Announcements: 
  Review the course calendar... I moved the
date of Exam 1 to 10/10/05 (Monday).

Questions I want to consider...


(1) What happens if you misspell the name of a function?
    What kind of error do you get?


(2) How can we read _lots of data_ into a program 
    (more than we might want to type all at once?)

What are your questions?

(1) formatting of numbers

 Q: If I have a variable that represents
    a number that will always be in the range
    13.00 to 35.00, what format specifier
    (percent-thingy) should I use to print it?

 A: The numbers in that range take up 
    5 characters, and have 2 after the decimal
    point.  (We we say "take up 5 chars", we
    include the decimal point as one of the
    characters)

           ++-- 2 after the decimal point 
           ||
           vv      
   so   35.00
        <-5->    5 characters in all

   So the format specifier we want is:

   for float: printf("The value is: %5.2f\n",ourVariable);

   for double:printf("The value is: %5.2lf\n",ourVariable);


   Now: the exam question is:

   Print x=1234.56;

     4 digits before, 2 after the decimal point

    double x = 1234.56;
    printf("x=____\n",x);

    Fill in the blank: ______  Answer: %7.2lf

   Suppose I want an integer, and I want it take
   up 5 spaces.

   The value is:     8 
   The value is:    68 
   The value is: 12345

   So, I want to print some integer values, but
   I want to be sure that they all line up.   
   The space for the values will be 5 characters
   wide, and the value will be "right justified"

   I also want one blank in front:

   int x;
   printf("The value is:______",x);
 
   What goes in the blank?  
   %5d with a space in front, like this:

   printf("The value is: %5d",x);

 
   (2) Formatting dollar amounts

  Question:

    Goal 10 on project 1 says that you should know how to: print a
    float or double as a dollar amount, appropriately formatted.

   double priceOfJeep = 35000.99;

   printf("The Jeep costs: $%8.2lf\n",priceOfJeep);

   
   float priceOfJeep = 35000.99;

   printf("The Jeep costs: $%8.2f\n",priceOfJeep);

   


(1) What happens if you misspell the name of a function?
    What kind of error do you get?

   What do we mean by a function?

   void printStars(void)
   {
     printf("***************************************\n");
   }

   int main(void)
   {
     printStars();
     printf("*     WELCOME TO MY PROGRAM!!!        *\n");
     printStars();

     printf("\n\n\n");

     printStars();
     printf("*       I hope you enjoyed it!!!      *\n");
     printStars();

     return 0;

   }


If we change the name of the function calls to printDecorativeLine,
but don't change the function definition, we get an error like this:

> make printStarExample
cc    -o printStarExample printStarExample.c 
"printStarExample.c", line 14: warning: implicit function declaration: printDecorativeLine
Undefined                       first referenced
 symbol                             in file
printDecorativeLine                 printStarExample.o
ld: fatal: Symbol referencing errors. No output written to printStarExample
*** Error code 1
make: Fatal error: Command failed for target `printStarExample'
> 


To understand this error, we need to understand the
four  phases of the compiler:

(1) preprocessor

(2) parsing 

(3) code generation (writing the .o files)

(4) linking

We will pick up there next time (Wednesday)