Consider the following statements about the use of backpatching in a compiler:
(I) Backpatching can be used to generate code for Boolean expression in one pass.
(II) Backpatching can be used to generate code for flow-of-control statements in one pass.
Which ONE of the following options is CORRECT?

The correct option is Both (I) and (II) are correct.

To understand why both statements are correct, let us analyze the concept of backpatching and its application in compiler design.

What is Backpatching?
In a single-pass compiler, code is generated as the source program is being parsed. A primary challenge in one-pass code generation is handling target addresses for jumps (jumps in Boolean expressions or flow-of-control constructs). For example, when generating code for a forward jump, the target instruction address is not yet known because that target code has not yet been compiled.
Backpatching is a systematic technique used to solve this issue. Instead of waiting for a second pass, the compiler leaves the target address of a jump instruction blank (or puts it in a placeholder list) when the jump is first generated. Later, when the target instruction is finally synthesized and its address becomes known, the compiler goes back and "patches" (fills in) the correct target address into all the instructions that were waiting for it. This allows syntax-directed translation to generate intermediate code in a single pass.

Analysis of Statement (I):
Statement (I) states: "Backpatching can be used to generate code for Boolean expression in one pass."
Boolean expressions are often evaluated using short-circuit evaluation (e.g., in $A\vee B$, if $A$ is true, the rest of the expression is not evaluated). This requires conditional jumps. Since the destination of these jumps (such as the start of the code representing the "true" or "false" exits) is determined later during syntax analysis, backpatching is used to manage lists of jumps (known as truelist and falselist) and fill in their target addresses in one pass. Therefore, Statement (I) is correct.

Analysis of Statement (II):
Statement (II) states: "Backpatching can be used to generate code for flow-of-control statements in one pass."
Flow-of-control statements like if-then, if-then-else, while-do, and repeat-until require jumps to transfer control. For instance, in a while loop, a conditional jump exits the loop if the condition is false. The target address for exiting the loop is only known after the entire body of the loop has been compiled. By maintaining a list of instructions that need to jump to this exit point (often called a nextlist) and patching the exit address once it is generated, backpatching enables one-pass code generation for these control flow statements. Therefore, Statement (II) is correct.

Since both statements (I) and (II) are correct, the correct option is indeed Both (I) and (II) are correct.