Control Instructions Questions and Answers

Q: We want to test whether a value lies in the range 2 to 4 or 5 to 7. Can we do this using a switch?

Correct answer: YesA switch cannot test a range directly, but the ranges here are small and the values are integers, so each can be listed as its own label with fall-through:case 2: case 3: case 4: /* first range */ break;case 5: case 6: case 7: /* second range */ break;This works because a label with no statements falls through to the next. For a wide or non-integer range, an if is the only option.

Q: By default, the data type of a constant without a decimal point is int, whereas the one with a decimal point is a double.

Correct answer: YesAn unsuffixed integer literal such as 10 has type int, and one with a decimal point such as 3.14 has type double - not float, which catches many people out. Suffixes override this: 10L, 10U, 3.14f.

Q: In the loop construct for(exp1; exp2; exp3), which part is always executed exactly once?

Correct answer: exp1exp1, the initialisation, is evaluated once before the loop starts and never again. exp2, the condition, is evaluated before every pass - at least once, and once more than the body runs. exp3, the update, runs after each pass, so it may not run at all if the condition fails immediately.

Q: The continue statement cannot be used with

Correct answer: switchcontinue means “begin the next iteration”, so it belongs to the three loops. A switch has no iterations, so a continue written inside one is either applied to an enclosing loop or, if there is none, rejected. break, by contrast, works in all four.

Q: Which keyword can be used for coming out of recursion?

Correct answer: returnRecursion is unwound by return: the base case returns instead of calling again, and each frame then returns in turn. break applies to loops and switches, not to function calls, and exit() would abandon the whole program rather than come back.

Q: goto can be used to jump from main into another function.

Correct answer: FALSEgoto can only reach a label in the same function; labels have function scope and are invisible outside it. Jumping between functions would leave the stack in an inconsistent state. Where a non-local jump really is needed, setjmp and longjmp provide a disciplined version of it.

Q: Which of the following is an invalid if-else statement?

Correct answer: if (if (a == 1)){}An if is a statement, and the parentheses of an if must contain an expression - so an if cannot appear there. The other three are fine: any scalar expression will do as a condition, including a cast and a function call.

Q: A switch statement accepts a controlling expression of type

Correct answer: All of the aboveThe controlling expression must be of integer type, and int, char and long all qualify - as do short and enumerations, with the smaller types promoted to int. Only the floating-point types are excluded.

Q: Which loop is guaranteed to execute at least once?

Correct answer: do whileA do-while tests its condition after the body, so the body always runs at least once. for and while test first, and so may not run at all. This makes do-while the natural choice for reading input and then validating it.

Q: A labelled statement consists of an identifier followed by

Correct answer: :A label is an identifier followed by a colon - here: - marking a point that goto can jump to. The same colon form is used by case and default labels inside a switch. Labels have function scope, so a goto can only reach one in the same function.

101.

We want to test whether a value lies in the range 2 to 4 or 5 to 7. Can we do this using a switch?

A.Yes
B.No

Answer: A

Correct answer: Yes

A switch cannot test a range directly, but the ranges here are small and the values are integers, so each can be listed as its own label with fall-through:

case 2: case 3: case 4: /* first range */ break; case 5: case 6: case 7: /* second range */ break;

This works because a label with no statements falls through to the next. For a wide or non-integer range, an if is the only option.

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102.

By default, the data type of a constant without a decimal point is int, whereas the one with a decimal point is a double.

A.Yes
B.No

Answer: A

Correct answer: Yes

An unsuffixed integer literal such as 10 has type int, and one with a decimal point such as 3.14 has type double - not float, which catches many people out. Suffixes override this: 10L, 10U, 3.14f.

Discuss in Forum

103.

In the loop construct for(exp1; exp2; exp3), which part is always executed exactly once?

A.exp1
B.exp3
C.exp1 and exp3
D.exp1, exp2 and exp3

Answer: A

Correct answer: exp1

exp1, the initialisation, is evaluated once before the loop starts and never again. exp2, the condition, is evaluated before every pass - at least once, and once more than the body runs. exp3, the update, runs after each pass, so it may not run at all if the condition fails immediately.

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104.

The continue statement cannot be used with

A.for
B.while
C.do while
D.switch

Answer: D

Correct answer: switch

continue means “begin the next iteration”, so it belongs to the three loops. A switch has no iterations, so a continue written inside one is either applied to an enclosing loop or, if there is none, rejected. break, by contrast, works in all four.

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105.

Which keyword can be used for coming out of recursion?

A.return
B.break
C.exit
D.both A and B

Answer: A

Correct answer: return

Recursion is unwound by return: the base case returns instead of calling again, and each frame then returns in turn. break applies to loops and switches, not to function calls, and exit() would abandon the whole program rather than come back.

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106.

goto can be used to jump from main into another function.

A.TRUE
B.FALSE
C.May Be
D.Can't Say

Answer: B

Correct answer: FALSE

goto can only reach a label in the same function; labels have function scope and are invisible outside it. Jumping between functions would leave the stack in an inconsistent state. Where a non-local jump really is needed, setjmp and longjmp provide a disciplined version of it.

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107.

Which of the following is an invalid if-else statement?

A.if (if (a == 1)){}
B.if (a){}
C.if ((char) a){}
D.if (func1 (a)){}

Answer: A

Correct answer: if (if (a == 1)){}

An if is a statement, and the parentheses of an if must contain an expression - so an if cannot appear there. The other three are fine: any scalar expression will do as a condition, including a cast and a function call.

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108.

A switch statement accepts a controlling expression of type

A.int
B.char
C.long
D.All of the above

Answer: D

Correct answer: All of the above

The controlling expression must be of integer type, and int, char and long all qualify - as do short and enumerations, with the smaller types promoted to int. Only the floating-point types are excluded.

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109.

Which loop is guaranteed to execute at least once?

A.for
B.while
C.do while
D.None of the above

Answer: C

Correct answer: do while

A do-while tests its condition after the body, so the body always runs at least once. for and while test first, and so may not run at all. This makes do-while the natural choice for reading input and then validating it.

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110.

A labelled statement consists of an identifier followed by

Answer: B

Correct answer: :

A label is an identifier followed by a colon - here: - marking a point that goto can jump to. The same colon form is used by case and default labels inside a switch. Labels have function scope, so a goto can only reach one in the same function.

Discuss in Forum

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