why default switch c++ code example

Example 1: switch c++

switch(expression) {
   case 1:
      //equivalent to if(expression == 1){//do someting...}
      //do something...
      break; 
    //if case 1 is true the rest of the statments arn't 
    //evaluated because of the break
   case 45:
      //equivalent to else if(expression == 45){//do someting...}
      //do something...
      break;
    
   // you can have any number of case statements and default has to be last
   default :
      // equivalent to else{//do someting...}
      //do something...
}

switch(expression) {
   case 1:
      //equivalent to if(expression == 1){//do someting...}
      //do something...
   case 45:
      //equivalent to if(expression == 45){//do someting...}
      //do something...
   default :
      //always runs if there are no breaks in any of the cases
      //do something...
}

//modification of answer by Homeless Hoopoe

Example 2: case label in c++

switch(foo) {
  case 1:
    int i = 42; // i exists all the way to the end of the switch
    dostuff(i);
    break;
  case 2:
    dostuff(i*2); // i is *also* in scope here, but is not initialized!
}