Problem-1

import java.util.Scanner;
class caluculator{
 double a,b;
 caluculator(double a, double b){
   this.a=a;
   this.b=b;
 }
 double add(){ retuen a+b; }
 double sub(){ retuen a-b; }
 double mul(){ retuen a*b; }
 double div(){ retuen a/b; }
}
 plublic class calc{
   
   public static void main(String args[]){
      Scanner sr= new Scanner(System.in);
      System.out.print("enter a");
      Double a = input.nextDouble();
      System.out.print("enter b");
      Double b = input.nextDouble();
      System.out.print("enter the operator(+,-,*,/) : ");
      String op=sr.next();
      Double c=0;
      
      caluculator obj=new calculator(a,b);
      switch(op){
          case "+": c=obj.add(); break;
          case "-": c=obj.sub(); break;
          case "*": c=obj.mul(); break;
          case "/": c=obj.div(); break;
          default: system.out.println("invalid operation");
        }
        
        System.out.println(a + op + b "=" + c );
        
    }
 }