LEC20080908 - Introduction to Computer Programming...

Introduction to Computer Programming
September 8, 2008
1 Required readings
How many lines of code have you written? Let n be your answer. If n is zero,
you must read Chapter 2 of the textbook twice carefully. If n is between 1 and
1 , 000, you should read Chapter 2 once. If n is greater than 1 , 000, you can
safely ignore Chapter 2, and proceed to Chapter 3.
2 Convert the above requirements to C code
The requirements in Section 1 can be easily converted to a C program, which,
based on our input, n , tells us what we should do. read.c is the source file for
the program. See Section 3 for detailed explanations.
/* read.c */
#include <stdio.h>
void read_ch2_twice()
{
printf(‘‘:( I must read Chapter 2 twice carefully!\n’’);
}
void read_ch2_once()
{
printf(‘‘I should read Chapter 2 once.\n’’);
}
void ignore_ch2()
{
printf(‘‘:) I can safely ignore Chapter 2.\n’’);
}
/*
1

* Input the number of lines of code that you have written. Hit Enter
* key. Follow the instructions given by the computer.
*/
int main()
{
int n;
printf(‘‘How many lines of code have you written? ‘‘);
if (scanf(‘‘%d’’, &n) < 1 || n < 0)
return 1;
if (n == 0) /* no lines? */
read_ch2_twice();
if (n > 0 && n <= 1000) /* some lines? */
read_ch2_once();
if (n > 1000) /* enough lines? */
ignore_ch2();
return 0;
}
3 Explanation
When we see a /* */ pattern, this is a C’s comment. The comment helps us
(not computers) understand the code. As we will see below, a comment may
occupy only one line, or may occupy multiple lines.
/* read.c */
/*
* Input the number of lines of code that you have written. Hit Enter
* key. Follow the instructions given by the computer.
*/
When we see #include , this is a C’s preprocessor directive. #include
<stdio.h> inserts the contents from the file stdio.h into the current file,
read.c . If we check stdio.h , we will find this line:
extern int printf (__const char *__restrict __format, ...);