switch case in C
Switch case statements are a substitute for long if statements that compare a
variable to several "integral" values ("integral" values are simply values
that can be expressed as an integer, such as the value of a char). The basic format for using switch case is
outlined below. The value of the variable given into switch is compared to
the value following each of the cases, and when one value matches the value of
the variable, the computer continues executing the program from that point.
switch ( <variable> ) {
case this-value:
Code to execute if <variable> == this-value
break;
case that-value:
Code to execute if <variable> == that-value
break;
...
default:
Code to execute if <variable> does not equal the value following any of the cases
break;
}
The condition of a switch statement is a value. The case says that if it has
the value of whatever is after that case then do whatever follows the colon.
The break is used to break out of the case statements. Break is a keyword that
breaks out of the code block, usually surrounded by braces, which it is in. In
this case, break prevents the program from falling through and executing the
code in all the other case statements. An important thing to note about the
switch statement is that the case values may only be constant integral
expressions. Sadly, it isn't legal to use case like this:
int a = 10;
int b = 10;
int c = 20;
switch ( a ) {
case b:
/* Code */
break;
case c:
/* Code */
break;
default:
/* Code */
break;
}
The default case is optional, but it is wise to include it as it handles any
unexpected cases. It can be useful to put some kind of output to alert you to
the code entering the default case if you don't expect it to. Switch
statements serve as a simple way to write long if statements when the
requirements are met. Often it can be used to process input from a user.
Below is a sample program, in which not all of the proper functions are
actually declared, but which shows how one would use switch in a program.
#include <stdio.h>
void playgame()
{
printf( "Play game called" );
}
void loadgame()
{
printf( "Load game called" );
}
void playmultiplayer()
{
printf( "Play multiplayer game called" );
}
int main()
{
int input;
printf( "1. Play game\n" );
printf( "2. Load game\n" );
printf( "3. Play multiplayer\n" );
printf( "4. Exit\n" );
printf( "Selection: " );
scanf( "%d", &input );
switch ( input ) {
case 1: /* Note the colon, not a semicolon */
playgame();
break;
case 2:
loadgame();
break;
case 3:
playmultiplayer();
break;
case 4:
printf( "Thanks for playing!\n" );
break;
default:
printf( "Bad input, quitting!\n" );
break;
}
getchar();
}
This program will compile, but cannot be run until the undefined functions are
given bodies, but it serves as a model (albeit simple) for processing input.
If you do not understand this then try mentally putting in if statements for
the case statements. Default simply skips out of the switch case construction
and allows the program to terminate naturally. If you do not like that, then
you can make a loop around the whole thing to have it wait for valid input.
You could easily make a few small functions if you wish to test the code.
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