JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III PRINCIPLES OF PROGRAMMING LANGUAGES Previous Question Paper (October - 2020 - R13)

The dangling else problem arises in standard grammars because an else clause can be associated with multiple if statements. To resolve this, we must distinguish between matched statements (those where every if has a corresponding else) and unmatched statements. An unambiguous grammar is defined as follows:

In this grammar, an unmatched statement cannot appear before an else clause, forcing the else to bind to the closest preceding if statement.

Language implementation methods define how source code is transformed into executable machine code. The three primary methods are:

• Compilation: The source program is translated into machine code by a compiler. The resulting object code is executed directly by the hardware. This approach offers high execution speed but requires a separate compilation step before execution.
• Pure Interpretation: The source program is executed by an interpreter, which acts as a software simulation of a computer. The interpreter fetches, decodes, and executes instructions one by one. This allows for easy debugging and platform independence but is significantly slower than compiled code.
• Hybrid Implementation: This method translates high-level source code into an intermediate language (e.g., bytecode), which is then interpreted by a virtual machine. This provides a balance between the portability of interpretation and the efficiency of compilation. Examples include Java (JVM) and Python.