What is the difference between plc,scada and DCS?

In my opinion 

Simply

PLC .. programable logic control , it's consists of many inputs ( switches, sensors,p.b .....ets )  and after programing CPU transferred output to  (Motors, Valves open/close....ets) 

LIMITED CONTRL

Plc it's the main part of both ( DCS&SCADA) for an example if you want connect that PLC with a monitor for controlling like motor start/stop or Valve open/close by the operator your system now is SCADA system SCADA means supervisory control and data acquisition and if you want to use more PLC's with more I/O with some monitors HMI's for controlling your system now transfered to DCS

DCS

DCSs use multi-tasking operating systems ,DCSs allow centralized configuration from the operator or engineering,DCSs have user-friendly configuration tools,DCSs allow graphical configuration

PLC is basically a controller to perform different actions on inputs and outputs according to programming. While SCADA is a way of implementation of your project and it contains multiple stages, top level stages is the server and a user interface, second level stage is intelligent devices stage which would be having PLCs, third level stage usually contain sensors and remote terminal units and forth level stage is equipped with field devices to be controlled. DCS is fully advanced system consisting of hundreds of SCADAs

PLC for digital inputs control usually for programmable sequence

Scadda is a remote control usually for oil & Gas wells & pipelines

DCS is the distributed control system usually in Main Control Room

Instrumentation are for controlling plants parameters

PLC is a programmable logic controller which can handle the binary input and output of the logic statement which are stored in its memory.its a digitally operating system which are logic stored in its memory by programming system.DCS Distributed control system its control all types of process variable at a time through this we can control the whole plant,we can see the status of plant,and handling unit.In PLC the Scan time is less.but the scan time of DCS is high.Because it Control the whole plant. So in safety loop we used PLC

01.A programmable logic controller, PLC, or programmable controller is a digital computer used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many machines, in many industries.                                                                                                      02.scada generally refers to an industrial computer system that monitors and controls a process

03.A distributed control system (DCS) is a control system for a process or plant, wherein control elements are distributed throughout the system. This is in contrast to non-distributed systems,

i am industrial automation engineering and i think to study in America with control systems such as ( SCAD/ BMS / smart home) or one of these.

But do you advise me and what its academic  name to study like these systems and not a requirement master may tutorial is enough  ??

PLC is the programmmable logic controller.

SCADA is a monitoring system used with PLC.

DCS means distributive control system.

DCS stands for distributed Control System, controlling is performed by embedded system (Microcontroller based or Microprocessor based controlling unit for device or instruments from which data is to be collect. It provides very intelligent analog control capability. It is very sensitive for HMI (Human machine Interface) for easy and smooth control of proces whereas PLC SCADA is concered they operate uses a programmable memory for the internal storage of instructions for implementing specific functions, such as logic, sequencing, timing, counting and arithmetic, to control through digital or analog input/output, various types of machines or process

plc is a device  rbased on tight or extensive control  system but Scada is basically a software observe operation of plc , DCS is considered a very tight control system which have more features of communcation more than plc

PLC is a device that makes SCADA and DCS. While SCADA and DCS are complete monitoring and control systems with upto millions of I/Os

All have the same similarities except plc is a programming device like a computer dcs is a panel where whole operation is watched for proper functioning and scada is a suoervisory computer linked to dcs