main.c.html

1	#include <stdio.h>
2	#include <stdlib.h>
3	
4	#define MONDAY 1
5	#define TUESDAY 2
6	#define WEDNESDAY 3
7	#define THURSDAY 4
8	#define FRIDAY 5
9	#define SATURDAY 6
10	#define SUNDAY 7
11	#define NO_DAY 8
12	
13	int main(int argc, char *argv[])
14	{
15	  int day = MONDAY;
16	  for(day = MONDAY;day <= NO_DAY;day++)
17	  {
18	    switch(day)
19	    {
20	      case MONDAY:
21	        printf("It's Monday, off to work\n");
22	        break;
23	      case TUESDAY:
24	        printf("It's Tuesday, long week ahead\n");
25	        break;
26	      case WEDNESDAY:
27	        printf("It's Wednesday, halfway there\n");
28	        break;
29	      case THURSDAY:
30	        printf("It's Thursday, one more day to go\n");
31	        break;
32	      case FRIDAY:
33	        printf("Thank Crunchie, it's Friday\n");
34	        break;
35	      case SATURDAY: /*This is an example of a drop through*/
36	      case SUNDAY:
37	        printf("It's the weekend, let's live it up\n");
38	        break;
39	      default:
40	        printf("Hey! This day cannot exist\n");
41	    }
42	  }
43	  system("PAUSE");	
44	  return 0;
45	}

`Purpose of the program`

This program prints out each day of the week with a little comment beside it. It demonstrates the usage of the switch statement. It also demonstrates a drop through in line 35 which cause the same message for Saturday and Sunday to be printed out.

`Break down of the code`

Line 1 - This line starts with a '#' hash sign which indicates that it is a preprocessor directive. The #include directive instructs the preprocessor to copy the contents of the following file into this source code file at this point. The filename is surrounded with '<>' brackets this instructs the preprocessor to look in the system 'include' directory first for this file. So this line copies the contents of the file 'stdio.h' into the source code file at this point before compiling starts. The file 'stdio.h' contains the declaration of many basic input output functions that are used in C programs.

Line 2 - This line works in the same manner as line 1. The difference is that the preprocessor copies the contents of the file 'stdlib.h' in to the source code at this point before compiling starts. The file 'stdlib.h' contains the declaration of many basic functions used by C programs.

Line 3 - Is blank.

Line 4 - This line also starts with a '#' hash sign so is again a preprocessor directive. This one tells the preprocessor that everywhere it finds 'MONDAY' in the source code replace it with the value 1.

Line 5 - Like line 4 this one tells the preprocessor to replace all occurrences of 'TUESDAY' with the value 2.

Line 6 - Like line 4 this one tells the preprocessor to replace all occurrences of 'WEDNESDAY' with the value 3.

Line 7 - Like line 4 this one tells the preprocessor to replace all occurrences of 'THURSDAY' with the value 4.

Line 8 - Like line 4 this one tells the preprocessor to replace all occurrences of 'FRIDAY' with the value 5.

Line 9 - Like line 4 this one tells the preprocessor to replace all occurrences of 'SATURDAY' with the value 6.

Line 10 - Like line 4 this one tells the preprocessor to replace all occurrences of 'SUNDAY' with the value 7.

Line 11 - Like line 4 this one tells the preprocessor to replace all occurrences of 'NO_DAY' with the value 8. This value is used in the for loop in line 16 as the value the loop should terminate on.

Line 12 - Is blank.

Line 13 - This line contains the start of our definition of the main function. As you can see main returns an int value. This value indicates to the operating system whether or not the program has terminated normally. The main function also takes two parameters these contain any command line options that are sent to you program when it starts. E.g. if you start notepad from the command line you would write notepad if you want to start notepad with a file to edit you would write notepad readme.txt. readme.txt would be a command line option. This is not a subject that will be considered further in the book so you may wish to find out more yourself.

Line 14 - This line contains the opening brace of the main function. There must be a closing brace to match every opening brace and vice versa. The closing brace is on line 13.

Line 15 - This line declares a variable of type integer and names it day. Then it sets the value of day to be equal to MONDAY which will be replaced by the preprocessor with the value 1.

Line 16 - In this line we set up a for loop. The first argument is our new variable day. It may seem superfluous to again assign the value MONDAY to the variable, but getting in a habit of doing so helps avoid problems with uninitilised variables. The second argument checks that the value of the variable is lower than NO_DAY which is our terminating value. The third argument increments the value of the variable, therefore making it equal to TUESDAY, WEDNESDAY, etc.

Line 17 - This line contains the opening brace of the for loop block. There must be a closing brace to match every opening brace and vice versa. The closing brace is on line 42.

Line 18 - This line contains the switch statement. The value within the curved brackets is the value which will be checked in the case part of the switch statement. In this example we will be checking the value of the variable day. This of course will be different each time the loop executes.

Line 19 - This line contains the opening brace of the switch statement block. There must be a closing brace to match every opening brace and vice versa. The closing brace is on line 41.

Line 20 - This line contains the first case statement. If the value of the variable in the switch statement is equal to the value specified in the case statement in the case MONDAY ( or 1) then the statement(s) following the colon ':' will be executed. If they are unequal then the next case statement will be checked.

Line 21 - This line uses the function printf() which is found in the stdio.h header file. This function is then instructed to print "It's Monday, off to work\n" on to the screen. Since there is a new line marker '\n' after this any further output will appear on the same line directly below this.

Line 22 - This line contains the break statement. This is vital to remember, it you omit this then the order of execution drops through to the next case statement. If we omitted this then the program would print out the message in line 21, followed by the message in line 24.

Line 23 - This line contains a case statement. If the value of the variable in the switch statement is equal to the value specified in the case statement in the case TUESDAY ( or 2) then the statement(s) following the colon ':' will be executed. If they are unequal then the next case statement will be checked.

Line 24 - This line uses the function printf() which is found in the stdio.h header file. This function is then instructed to print "It's Tuesday, long week ahead\n" on to the screen. Since there is a new line marker '\n' after this any further output will appear on the same line directly below this.

Line 25 - This line contains the break statement. This is vital to remember, it you omit this then the order of execution drops through to the next case statement.

Line 26 - This line contains a case statement. If the value of the variable in the switch statement is equal to the value specified in the case statement in the case WEDNESDAY ( or 3) then the statement(s) following the colon ':' will be executed. If they are unequal then the next case statement will be checked.

Line 27 - This line uses the function printf() which is found in the stdio.h header file. This function is then instructed to print "It's Wednesday, half way there\n" on to the screen. Since there is a new line marker '\n' after this any further output will appear on the same line directly below this.

Line 28 - This line contains the break statement. This is vital to remember, it you omit this then the order of execution drops through to the next case statement.

Line 29 - This line contains a case statement. If the value of the variable in the switch statement is equal to the value specified in the case statement in the case THURSDAY ( or 4) then the statement(s) following the colon ':' will be executed. If they are unequal then the next case statement will be checked.

Line 30 - This line uses the function printf() which is found in the stdio.h header file. This function is then instructed to print "It's Thursday, one more day to go\n" on to the screen. Since there is a new line marker '\n' after this any further output will appear on the same line directly below this.

Line 31 - This line contains the break statement. This is vital to remember, it you omit this then the order of execution drops through to the next case statement.

Line 32 - This line contains a case statement. If the value of the variable in the switch statement is equal to the value specified in the case statement in the case FRIDAY ( or 5) then the statement(s) following the colon ':' will be executed. If they are unequal then the next case statement will be checked.

Line 33 - This line uses the function printf() which is found in the stdio.h header file. This function is then instructed to print "Thank Crunchie, it's Friday\n" on to the screen. Since there is a new line marker '\n' after this any further output will appear on the same line directly below this.

Line 34 - This line contains the break statement. This is vital to remember, it you omit this then the order of execution drops through to the next case statement.

Line 35 - This line contains a case statement. If the value of the variable in the switch statement is equal to the value specified in the case statement in the case SATURDAY ( or 6) then the statement(s) following the colon ':' will be executed. If they are unequal then the next case statement will be checked. However since there are no statements following the colon execute will drop through to the next case statement. This causes the same value to be printed out for SATURDAY and SUNDAY.

Line 36 - This line contains a case statement. If the value of the variable in the switch statement is equal to the value specified in the case statement in the case SUNDAY ( or 7) then the statement(s) following the colon ':' will be executed. If they are unequal then the next case statement will be checked, which will be the default statement.

Line 37 - This line uses the function printf() which is found in the stdio.h header file. This function is then instructed to print "It's the weekend, let's live it up\n" on to the screen. Since there is a new line marker '\n' after this any further output will appear on the same line directly below this.

Line 38 - This line contains the break statement. This is vital to remember, it you omit this then the order of execution drops through to the next case statement.

Line 36 - This line contains the default case statement. If the value of the variable in the switch statement is not equal to any of the above case statements then the statement(s) following the colon ':' will be executed. The default usually exists to catch error values such as this example, values which you don't care about or a set of values that require the same processing no matter what they are.

Line 37 - This line uses the function printf() which is found in the stdio.h header file. This function is then instructed to print "Hey! This day cannot exist\n" on to the screen. Since there is a new line marker '\n' after this any further output will appear on the same line directly below this.

Line 41 - This line contains the closing brace of the switch statement block.

Line 42 - This line contains the closing brace of the for loop block.

Line 43 - The function system("PAUSE") is used to pause the program until a key is pressed. The reason for this is that under windows the console would open, the text would be output to it then it would close. You would see little more than a flash on the screen as this happened. Try commenting out the line to see this happen.

Line 44 - The return statement is used at the end of functions to return an item of data. This item of data should match the return type declared at the start of the function. We are in the main function and as you can see in line 6 this should be an integer. The return statement marks the end of the function any code after this will not be executed your compiler will usually warn you of this when you compile the program. The value 0 is a value that tells the operating system that the program has terminated normally.

Line 45 - This line contains the closing brace of the main function.