Control Instructions Questions and Answers

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.

Q: #include <stdio.h> int i; int main() { if (i); else printf("Else"); return 0; } What is correct about the above program?

Correct answer: Else block is executedi is a global, so it is zero-initialised - not indeterminate, which is what makes the outcome predictable. The condition is therefore false. The semicolon after if (i) is the empty statement that forms the if branch, and the else attaches to it perfectly legally, so the else branch runs.

Q: Output? #include <stdio.h> int main() { int c = 5, no = 10; do { no /= c; } while(c--); printf ("%d\n", no); return 0; }

Correct answer: Runtime ErrorThe loop divides no by c and then tests c--, so c falls 5, 4, 3, 2, 1, 0. On the pass after the test that saw c equal to 1, c is 0 - and no /= 0 is integer division by zero, which the hardware traps. The compiler cannot see it, so it is a run-time fault.

Q: What is the output of the below program? #include <stdio.h> int main() { int i = 0; switch (i) { case '0': printf("Geeks"); break; case '1': printf("Quiz"); break; default: printf("GeeksQuiz"); } return 0; }

Correct answer: GeeksQuiz'0' is a character constant, and its value is the ASCII code 48, not the number 0. Likewise '1' is 49. The controlling expression is 0, which matches neither, so control falls to default.

21.

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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22.

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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23.

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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24.

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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25.

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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26.

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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27.

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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28.

#include <stdio.h>
int i;
int main()
{
    if (i);
    else
        printf("Else");
    return 0;
}

What is correct about the above program?

A.If block is executed
B.Else block is executed
C.It is unpredictable as i is not initialized
D.Error: misplaced else

Answer: B

Correct answer: Else block is executed

i is a global, so it is zero-initialised - not indeterminate, which is what makes the outcome predictable. The condition is therefore false. The semicolon after if (i) is the empty statement that forms the if branch, and the else attaches to it perfectly legally, so the else branch runs.

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29.

Output?

#include <stdio.h>
int main()
{
    int c = 5, no = 10;
    do {
        no /= c;
    } while(c--);
  
    printf ("%d\n", no);
    return 0;
}

A.1
B.Runtime Error
C.Compiler Error

Answer: B

Correct answer: Runtime Error

The loop divides no by c and then tests c--, so c falls 5, 4, 3, 2, 1, 0. On the pass after the test that saw c equal to 1, c is 0 - and no /= 0 is integer division by zero, which the hardware traps. The compiler cannot see it, so it is a run-time fault.

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30.

What is the output of the below program?

#include <stdio.h>
int main()
{
    int i = 0;
    switch (i)
    {
        case '0': printf("Geeks");
                break;
        case '1': printf("Quiz");
                break;
        default: printf("GeeksQuiz");
    }
    return 0;
}

A.Geeks
B.Quiz
C.GeeksQuiz
D.Compile-time error

Answer: C

Correct answer: GeeksQuiz

'0' is a character constant, and its value is the ASCII code 48, not the number 0. Likewise '1' is 49. The controlling expression is 0, which matches neither, so control falls to default.

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