GATE CSE 1989 | Question: 4-v

Question

Is the following code template for the if-then-else statement correct? if not, correct it.

• $\text{if} \text{ expression then statement } 1$
  $\text{else statement }2$

Template:

Code for expression

• (*result in $E, E > O$ indicates true *)
• Branch on $E > O$ to $L1$
• Code for statement $1$
• $L1$: Code for statement $2$

Answer 1

The given template is wrong. The following should be correct:

Code for Expression

• Branch on $E>0$ to $L$
• Code for segment $2$
• Branch to $L1$
• $L$: Code for statement $1$
• $L1$:

Comments

That means ,  in template "condition statement 1" & " condition statement 2" should be swapped to make it correct.

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After swapping statement 1 and statement 2, an unconditional branch instruction should be also included after statement 2. Otherwise both the statements will get executed, which should not happen.

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Why would this →  L: Code for statement 1 execute again? after executing above code. L would execute then and then only when L is called particularly by IF right?

What is the significance of this line → Branch to L1 and L1 :

Please explain.

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ankit3009

I think it is for exit.

Answer 2

What is expected from the code:

“if expression is true execute statement 1, else execute statement 2.”

What given code is doing:

“if expression (E > 0) is true execute statement 2, else execute statement 1.”

Modified Template:

Code for expression

• (*result in E, E>O indicates true *)
• Branch on E>O to L1
• Code for statement 2
• L1: Code for statement 1