Control Instructions Questions and Answers

Q: Which of the following sentences are correct about a switch loop in a C program? 1. switch is useful when we wish to check the value of variable against a particular set of values. 2. switch is useful when we wish to check whether a value falls in different ranges. 3. Compiler implements a jump table for cases used in switch. 4. It is not necessary to use a break in every switch statement.

Correct answer: 1,3,41 is true - a switch compares the controlling expression against a set of discrete constants. 3 is true: where the labels are dense the compiler typically builds a jump table, which is why a switch can beat a chain of ifs. 4 is true: omitting break is legal and produces deliberate fall-through.2 is false. A switch cannot test a range - each value in the range needs its own label - which is what if-else if is for.

Q: Consider the following pseudocode: x:=1; i:=1; while (x ≤ 500) begin x := 2^x ; i:=i+1; end What is the value of i at the end of the pseudocode?

Correct answer: 5Each pass replaces x by \(2^x\), which grows extremely fast:after pass-1234x1241665536i12345The test \(x \le 500\) fails once x reaches 65536, and i is then 5.

Q: What will be the output of the program? #include <stdio.h> int main() { int i = 5; while(i-- >= 0) printf("%d,", i); i = 5; printf("\n"); while(i-- >= 0) printf("%i,", i); while(i-- >= 0) printf("%d,", i); return 0; }

Correct answer: 4, 3, 2, 1, 0, -1 4, 3, 2, 1, 0, -1i-- >= 0 tests the old value and then decrements, so the value printed is always one less than the value tested. Starting at 5 that gives 4, 3, 2, 1, 0 and finally -1 - the pass where the test saw 0. The loop then leaves i at -2. After i is reset to 5 the second loop prints the same line. The third loop then starts with i at -2, so its very first test fails and it prints nothing.

Q: Which of the following cannot be checked in a switch-case statement?

Correct answer: FloatA switch requires an integer controlling expression, so char, int and enumeration constants are all fine. float is not: exact equality against a case label would be unreliable for values that cannot be represented exactly in binary.

Q: How many times the while loop will get executed if a short int is 2 byte wide? #include <stdio.h> int main() { int j=1; while(j <= 255) { printf("%c %d\n", j, j); j++; } return 0; }

Correct answer: 255 timesj runs from 1 and the loop continues while j <= 255, so it executes for j equal to 1, 2, …, 255 - 255 passes. The width of a short is a red herring: j is declared int, and 255 is nowhere near the limit of either type.

Q: What is the output of this C code? void main() { int k; for (k = -3; k < -5; k++) printf("Hello"); }

Correct answer: NothingA for tests its condition before the first pass. With k at -3, the test k < -5 is already false, so the body never runs and nothing is printed. (Had it been a do-while, the body would have run once.)

Q: What is the output of the following C code? #include <stdio.h> int main() { int index; for(index=1; index<=5; index++) { printf("%d", index); if (index==3) continue; } }

Correct answer: 12345The continue is the last statement in the body, so it skips nothing - the next thing after it would have been the end of the iteration anyway. Every pass prints its index, giving 12345.

Q: A char variable can store either an ASCII character or a Unicode character.

Correct answer: FalseIn C a char is one byte - sizeof(char) is 1 by definition - and on ordinary implementations that is eight bits, giving 256 possible values. That is ample for ASCII, which uses only the codes 0 to 127, but Unicode defines over a million code points, so a single char cannot hold an arbitrary Unicode character. C provides other types for that work: wchar_t for wide characters, and since C11 char16_t and char32_t for UTF-16 and UTF-32 code units, declared in <uchar.h>. What a char array can hold is a Unicode character encoded in UTF-8, but that takes one to four char elements per character, not one - the character is spread across several bytes rather than stored in a single variable. The confusion usually comes from Java, where char is a 16-bit UTF-16 code unit and the statement would be much closer to true. In C it is false.

Q: A short integer is at least 16 bits wide and a long integer is at least 32 bits wide.

Correct answer: TrueThe standard sets minimum widths, not exact ones: short must be at least 16 bits and long at least 32, with int at least 16 and long long at least 64. It also requires the ordering char ≤ short ≤ int ≤ long ≤ long long. Actual widths vary by platform, which is why <stdint.h> offers fixed-width types.

21.

Which of the following sentences are correct about a switch loop in a C program?

1. switch is useful when we wish to check the value of variable against a particular set of values.

2. switch is useful when we wish to check whether a value falls in different ranges.

3. Compiler implements a jump table for cases used in switch.

4. It is not necessary to use a break in every switch statement.

A.1,2
B.1,3,4
C.2,4
D.2

Answer: B

Correct answer: 1,3,4

1 is true - a switch compares the controlling expression against a set of discrete constants. 3 is true: where the labels are dense the compiler typically builds a jump table, which is why a switch can beat a chain of ifs. 4 is true: omitting break is legal and produces deliberate fall-through.

2 is false. A switch cannot test a range - each value in the range needs its own label - which is what if-else if is for.

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22.

Consider the following pseudocode:

x:=1;
i:=1;
while (x ≤ 500)
begin
x := 2^x ;
i:=i+1;
end

What is the value of i at the end of the pseudocode?

Answer: B

Correct answer: 5

Each pass replaces x by \(2^x\), which grows extremely fast:

after pass	-	1	2	3	4
x	1	2	4	16	65536
i	1	2	3	4	5

The test \(x \le 500\) fails once x reaches 65536, and i is then 5.

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23.

In mathematics and computer programming, which is the correct order of mathematical operators ?

A.Addition, Subtraction, Multiplication, Division
B.Division, Multiplication, Addition, Subtraction
C.Multiplication, Addition, Division, Subtraction
D.Addition, Division, Modulus, Subtraction

Answer: B

Correct answer: Division, Multiplication, Addition, Subtraction

Multiplication and division sit at the same, higher precedence, and addition and subtraction at the same, lower one; within a level, evaluation runs left to right. The listed order reflects that grouping, which is what BODMAS and PEMDAS describe.

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24.

What will be the output of the program?

#include <stdio.h>
int main()
{
    int i = 5;
    while(i-- >= 0)
        printf("%d,", i);
    i = 5;
    printf("\n");
    while(i-- >= 0)
        printf("%i,", i);
    while(i-- >= 0)
        printf("%d,", i);
    return 0;
}

A.4, 3, 2, 1, 0, -14, 3, 2, 1, 0, -1
B.5, 4, 3, 2, 1, 05, 4, 3, 2, 1, 0
C.Error
D.5, 4, 3, 2, 1, 05, 4, 3, 2, 1, 05, 4, 3, 2, 1, 0

Answer: A

Correct answer: 4, 3, 2, 1, 0, -1 4, 3, 2, 1, 0, -1

i-- >= 0 tests the old value and then decrements, so the value printed is always one less than the value tested. Starting at 5 that gives 4, 3, 2, 1, 0 and finally -1 - the pass where the test saw 0. The loop then leaves i at -2. After i is reset to 5 the second loop prints the same line. The third loop then starts with i at -2, so its very first test fails and it prints nothing.

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25.

Which of the following cannot be checked in a switch-case statement?

A.Character
B.Integer
C.Float
D.enum

Answer: C

Correct answer: Float

A switch requires an integer controlling expression, so char, int and enumeration constants are all fine. float is not: exact equality against a case label would be unreliable for values that cannot be represented exactly in binary.

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26.

How many times the while loop will get executed if a short int is 2 byte wide?

#include <stdio.h>
int main()
{
    int j=1;
    while(j <= 255)
    {
        printf("%c %d\n", j, j);
        j++;
    }
    return 0;
}

A.Infinite times
B.255 times
C.256 times
D.254 times

Answer: B

Correct answer: 255 times

j runs from 1 and the loop continues while j <= 255, so it executes for j equal to 1, 2, …, 255 - 255 passes. The width of a short is a red herring: j is declared int, and 255 is nowhere near the limit of either type.

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27.

What is the output of this C code?

void main()

    {

        int k;

        for (k = -3; k < -5; k++)

            printf("Hello");

    }

A.Hello
B.Infinite hello
C.Run time error
D.Nothing

Answer: D

Correct answer: Nothing

A for tests its condition before the first pass. With k at -3, the test k < -5 is already false, so the body never runs and nothing is printed. (Had it been a do-while, the body would have run once.)

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28.

What is the output of the following C code?

#include <stdio.h>
int main()
{
int index;
for(index=1; index<=5; index++)
{
printf("%d", index);
if (index==3)
continue;
}
}

A.1245
B.12345
C.12245
D.12354

Answer: B

Correct answer: 12345

The continue is the last statement in the body, so it skips nothing - the next thing after it would have been the end of the iteration anyway. Every pass prints its index, giving 12345.

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29.

A char variable can store either an ASCII character or a Unicode character.

A.True
B.False

Answer: A

Correct answer: False

In C a char is one byte - sizeof(char) is 1 by definition - and on ordinary implementations that is eight bits, giving 256 possible values. That is ample for ASCII, which uses only the codes 0 to 127, but Unicode defines over a million code points, so a single char cannot hold an arbitrary Unicode character. C provides other types for that work: wchar_t for wide characters, and since C11 char16_t and char32_t for UTF-16 and UTF-32 code units, declared in <uchar.h>. What a char array can hold is a Unicode character encoded in UTF-8, but that takes one to four char elements per character, not one - the character is spread across several bytes rather than stored in a single variable. The confusion usually comes from Java, where char is a 16-bit UTF-16 code unit and the statement would be much closer to true. In C it is false.

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30.

A short integer is at least 16 bits wide and a long integer is at least 32 bits wide.

A.True
B.False

Answer: A

Correct answer: True

The standard sets minimum widths, not exact ones: short must be at least 16 bits and long at least 32, with int at least 16 and long long at least 64. It also requires the ordering char ≤ short ≤ int ≤ long ≤ long long. Actual widths vary by platform, which is why <stdint.h> offers fixed-width types.

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