Question

Using the virtual machine instructions, give an operational semantic definition of the following:

a. Java do-while
b. Ada for
c. C++ if-then-else
d. C for
e. Cswitch

Answer 1

Operational semantics define the execution steps of control structures in programming languages. For Java do-while, Ada for, C++ if-then-else, and C for and switch, these semantics describe how loops and conditional constructs operate at runtime in a sequential and conditional manner.

Step-by-step explanation:

The operational semantics of control structures in various programming languages specify how the instructions associated with these structures are executed by the virtual machine or compiler during the runtime of a program. Each language has its own specific implementation details, but the core ideas behind these constructs are often similar across languages.

The Java do-while loop is a post-tested loop which means it executes the body at least once before checking the condition. The operational semantics are as follows:

1. Execute the loop body.
2. Check the loop condition.
3. If the condition is true, go back to step 1; otherwise, exit the loop.

The Ada for loop is used for iterating over a range of values. The operational semantics are:

1. Initialize the loop counter to the starting value.
2. Check if the loop counter has surpassed the ending value.
3. If not, execute the body and increment the counter, then go back to step 2; otherwise, exit the loop.

The C++ if-then-else statement is a conditional branching construct that allows for two paths of execution based on a Boolean condition. Semantically:

1. Evaluate the condition.
2. If the condition is true, execute the 'then' block.
3. If the condition is false, execute the 'else' block (if it exists); otherwise, continue execution with the next statement.

The C for loop is a pre-tested loop with an initial setup, a condition check, and an iteration expression. Operational semantics:

1. Execute the initial setup once.
2. Check the condition.
3. If true, execute the loop body then the iteration expression and go back to step 2; otherwise, exit.

The C switch statement is a multi-way branch statement that selects one branch to execute based on the value of an expression. The semantics:

1. Evaluate the controlling expression.
2. Compare the result with each 'case' value.
3. Execute the matching case block. If no match is found and a 'default' case exists, execute the 'default' block.