Pushdown Automata MCQ Quiz Questions

Explanation
Pushdown Automata are equivalent to Context-Free Grammar. This is because both Pushdown Automata and Context-Free Grammar are formal models of computation that can generate and recognize context-free languages. Pushdown Automata use a stack to keep track of information, while Context-Free Grammar uses production rules to generate strings. Therefore, they are considered equivalent in terms of their computational power.

Explanation
A PDA, or Pushdown Automata, is a theoretical device used in computer science and formal language theory. It is a type of finite-state machine with an added stack, or pushdown stack, that allows for more complex computations. The stack enables the PDA to remember and manipulate data, making it more powerful than a regular finite-state machine. Therefore, "Pushdown Automata" is the correct definition for PDA.

Explanation
The correct answer is "Nondeterministic Pushdown Automata". NPDA stands for Nondeterministic Pushdown Automata, which is a theoretical model of computation used in computer science. It is a variation of a pushdown automaton, which is a type of finite state machine that can use a stack to store and retrieve information. In an NPDA, the next state of the machine is not uniquely determined by the current state and input symbol, allowing for multiple possible transitions. This non-determinism gives NPDA more computational power than deterministic pushdown automata.

Explanation
A PDA is a finite automata with a push-down stack. This means that it has a finite number of states and can transition between these states based on input symbols. Additionally, it has a stack that allows it to store and retrieve symbols. The stack can be used to remember information about previous inputs, making it more powerful than a regular finite automata. However, the stack itself has a finite capacity, which means that a PDA is ultimately limited in the amount of information it can remember and process. Therefore, the correct answer is "Finite".

Explanation
If a machine at the end of the string enters one of the final states, then the string is considered "Accepted". This means that the machine has successfully processed the string according to its rules and has reached a valid final state, indicating that the string satisfies the criteria or requirements set by the machine.

Explanation
The given operations "Insert," "Add," and "Delete" are not eligible in a PDA (Pushdown Automaton) as they are not standard operations performed in a PDA. However, "Push" is an eligible operation in a PDA as it refers to the process of pushing a symbol onto the stack of the automaton.

Explanation
The correct answer is "Both" because a pushdown automaton (PDA) can be either deterministic (DPDA) or nondeterministic (NPDA). A DPDA is a type of PDA that follows a deterministic set of rules to transition between states, while an NPDA is a type of PDA that can have multiple possible transitions from a given state. Therefore, both DPDA and NPDA are valid types of pushdown automata.

Explanation
A language is considered context-free if it can be accepted by a Pushdown Automaton (PDA). A PDA is a theoretical machine that has a stack to store and retrieve symbols. It can read input symbols, push symbols onto the stack, pop symbols from the stack, and transition between states based on the current input symbol and the top symbol of the stack. The fact that a language is accepted by a PDA means that it can be generated by a context-free grammar, which is a set of production rules that define the structure of the language. Therefore, the correct answer is PDA.

Explanation
DPDA stands for Deterministic Pushdown Automata. A pushdown automaton is a type of automaton that can recognize context-free languages. It consists of a finite state control, a stack, and an input tape. The term "deterministic" means that for each state and input symbol, there is at most one transition. In other words, the behavior of the automaton is uniquely determined by its current state and the symbol it reads from the input. Therefore, the correct answer is Deterministic Pushdown Automata.

Explanation
Pushdown Automata can manipulate the stack. This means that they can perform operations such as pushing new symbols onto the stack, popping symbols off the stack, or replacing symbols on the stack with other symbols. By manipulating the stack, a pushdown automaton can keep track of the context or history of the input it is processing, which allows it to recognize and accept certain types of languages that cannot be recognized by finite automata.