Programming with C/C++ Language
Introduction to the C++ Language
switch case in C++

1. Switch case

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 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.

Here is the basic format for using switch case :

 

switch (  ) {
case this-value:
  Code to execute if  == this-value
  break;
case that-value:
  Code to execute if  == that-value
  break;
...
default:
  Code to execute if  does not equal the 
  value following any of the cases
  break;
} 

The condition of a switch statement is a value.

The break is used to break out of the case statements.It is a keyword that breaks out of the code block. It prevents the program from falling through and executing the code in all the other case statements.

The case values may only be constant integral expressions. The following code is not allowed:

int x = 12;

switch ( a ) {
case x:
  // Code  ..
  break;
default:
  // Code .. 
  break;
} 

The default case is optional, but it is wise to include it as it handles any unexpected cases.

Switch statements serves 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.

2. Example

Here is an Example:

 
#include 

using namespace std;

void write()
{
    cout << "Write a poem";
}
void compose()
{
    cout << "Compose this poem ";
}
void sing()
{
    cout << "Sing the written composed poem ";
}
	
	
int main()
{
  int input;
  
  cout<<"1. Write a poem \n";
  cout<<"2. Compose the poem \n";
  cout<<"3. Sing the poem \n";
  cout<<"4. Quit\n";
  cout<<"Selection: "; 
  
  cin>> input;
  switch ( input ) {
  case 1: 
   write();
    break;
  case 2:
    compose ();
    break;
  case 3: 
    sing();
    break;
  case 4: 
    cout<<"The song is done .. !\n";
    break; 
	
  default: 
    cout<<"Error, incorrect input, quitting\n";
    break;
  }
  cin.get();
} 

This program will compile, but cannot be run until the is input is processed.

Default simply skips out of the switch case construction and allows the program to terminate naturally.