# Write ac program to convert cfg to pda

So on each move, we 1.

### Cfg to pda question

We have previously described the process of generating a string by left-most derivation as Begin with a string consisting only of the start symbol. Change state, and 2. Remember that a PDA transition can write any number of symbols to the stack. See Example 6. Here are two PDAs for L: and The idea in both of these machines is to stack the a's and match off the b's. The data structure used for implementing a PDA is stack. That automaton is, to all appearances, deterministic. On receiving 2, pop 1 from stack and goto next state Step On receiving 2 pop 1 from stack. Even messier, the multiple parallel transitions may manipulate the stack in different ways, leading to different stack contents for each of those parallel states. You can see that the solution attempted there is, at best, a textual hack. In fact, the set of languages that can be recognized by PDAs are the context-free languages of the previous module. Nevertheless, one can maintain knowledge of an empty stack by using a dedicated stack symbol, c, representing the "stack bottom" with the property that it is pushed onto an empty stack by a transition from the start state with no other outgoing or incoming transitions. The second version is deterministic in that the first b acts as a trigger to start matching off. The proof is in you textbook. On the other hand, this PDA is very definitely non-deterministic.

We could actually drop those productions without affecting the language accepted by the CFG we are going to generate. If not, stop the algorithm.

### Cfl to cfg conversion

Even messier, the multiple parallel transitions may manipulate the stack in different ways, leading to different stack contents for each of those parallel states. The variables in the leftmost derivation are encoding the contents that the PDA stack would have once it has recognized all of the terminal symbols to the left of the first variable. The last is the big change in the way that state transitions are dedermined. That automaton is, to all appearances, deterministic. Looking at the derivation, and comparing to the PDA, you can start to see what happens with this style of grammar construction. We have previously described the process of generating a string by left-most derivation as Begin with a string consisting only of the start symbol. When they're equal, no stack bottom is necessary. One of the problems associated with DFAs was that could not make a count of number of characters which were given input to the machine. Change state, and 2. This is the technique I have used in the examples above.

A PDA has an output associated with every input. Similarly, if the input is 1, then no matter what symbol is on top of the stack, we push a 1 onto the stack.

The empty stack is our key new requirement relative to finite state machines. In the above PDA, the only non-determinism is the issue of guessing the end of input; however this form of non-determinism is considered artificial.

Pick the leftmost variable occurrence in the current string. Go to step 6. Thereafter for every 1 as input a 0 is popped out of stack.

## Cfg to pda conversion example ppt

User can perform the basic push and pop operations on the stack which is use for PDA. Behavior of PDA The three groups of loop transitions in state q represent these respective functions: input a with no b's on the stack: push a input b with no a's on the stack: push b input a with b's on the stack: pop b; or, input b with a's on the stack: pop a For example if we have seen 5 b's and 3 a's in any order, then the stack should be "bbc". Acceptance by empty stack only or final state only is addressed in problems 3. Other strings in the language may require other productions. Q is a finite set of states. All the inputs are either pushed into a stack or just ignored. When they're unequal, you have to be prepared to recognize that the stacked a's have been completely matched or not. The last is the big change in the way that state transitions are dedermined. In fact, the set of languages that can be recognized by PDAs are the context-free languages of the previous module. Look at the transitions from q to itself. That leaves the question of knowing when we are done. If string is finished and stack is empty then string is accepted by the PDA otherwise not accepted. Replace the chosen occurrence of that variable by the right-hand side of the chosen production. Once you get to the final state, you can consume remaining b's and end marker. That transition triggers on every state transition including the start of the automaton.

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