List of websites for C-language preparation

1	GeeksforGeeks
2	Programiz
3	TutorialsPoint
4	Try to Program
5	MYCPLUS
6	C-Programming.com

List of websites for C++ -language preparation

1	GeeksforGeeks
2	Programiz
3	TutorialsPoint
4	LearnCpp.com
5	cplusplus.com
6	edabit

List of websites for Python preparation

1	GeeksforGeeks
2	Programiz
3	TutorialsPoint
4	learnpython.org

List of websites for Java preparation

1	GeeksforGeeks
2	Programiz
3	TutorialsPoint
4	learnjava.org
5	Learneroo

Best of luck