• Transition diagrams are powerful tool to represent the Regular expression 

• Transition diagram consists of states and edges

• A transition diagram starts with a start/ initial state and may have one or more final states

• During the process of scanning the input, 

1. States represent the condition when the lexeme matches the patterns

2. States are represented as nodes or circles

3. Final states are represented as double circle

• Transition from one state to another state is indicated with edges.

• Every edge is labeled by either a symbol or a set of symbols

Example: Transition diagram for C identifier

Solution: Here, A and B are the states and B represents the final state. Every edge is labeled with the symbol.