Control Instructions Questions and Answers

Q: If scanf() is used to store a value in a char variable then along with the value a carriage return also gets stored with it.

Correct answer: FalseNothing extra is stored. scanf("%c", &ch) reads exactly one character into the variable; the newline you typed afterwards is simply left in the input buffer, where it will be picked up by the next read. That is why a second %c so often appears to read nothing - it consumes the leftover newline.

Q: What will be the output of the program? #include <stdio.h> int main() { int x=1, y=1; for(; y; printf("%d %d\n", x, y)) { y = x++ <= 5; } printf("\n"); return 0; }

Correct answer: 2 1 3 1 4 1 5 1 6 1 7 0The third clause of the for is the printf, so the values are printed after each pass through the body. The body sets y to the result of x++ <= 5, which is 1 while the old x is at most 5. So the pairs printed are 2 1, 3 1, 4 1, 5 1, 6 1 - and on the pass where x is 6 the comparison fails, giving 7 0, after which the condition y is false and the loop ends.

Q: A do-while loop terminates when its controlling expression evaluates to

Correct answer: ZeroA loop continues while its condition is true, that is non-zero, and stops when it evaluates to zero. The do-while differs from the others only in when the test happens - after the body rather than before - so the body always runs at least once.

Q: #include <stdio.h> int main() { int i; if (printf("0")) i = 3; else i = 5; printf("%d", i); return 0; }

Correct answer: 03printf returns the number of characters written. It prints 0 - that is one character - and returns 1, which is true, so i becomes 3. The output is therefore the 0 from the condition followed by the 3: 03.

Q: What will be the output of the program? #include <stdio.h> int main() { int a = 300, b, c; if(a >= 400) b = 300; c = 200; printf("%d, %d, %d\n", a, b, c); return 0; }

Correct answer: 300, Garbage, 200The condition \(300 \ge 400\) is false, so b = 300 never runs - and b, an uninitialised automatic variable, holds whatever was on the stack. c = 200 is a separate statement outside the if, so it always executes.

Q: What will be the output of the program? #include <stdio.h> int main() { int i=3; switch(i) { case 1: printf("Hello\n"); case 2: printf("Hi\n"); case 3: continue; default: printf("Bye\n"); } return 0; }

Correct answer: Error: Misplaced continuecontinue asks for the next iteration of a loop, and a switch is not a loop - nor is there any loop around this one. The compiler therefore rejects it. break would have been legal, since break applies to a switch as well as to a loop.

Q: Point out the error, if any in the program. #include <stdio.h> int main() { int i = 1; switch(i) { printf("This is c program."); case 1: printf("Case1"); break; case 2: printf("Case2"); break; } return 0; }

Correct answer: No Error and prints "Case1"The printf before the first case is legal but unreachable: a switch transfers control straight to a matching label, so nothing before the first label ever runs. i is 1, so case 1 executes and the break ends the switch.

Q: What is the output of this C code? void main() { int i = 0; if (i == 0) { printf("Hello"); continue; } }

Correct answer: Compile time errorcontinue is meaningful only inside a loop: it asks for the next iteration, and here there is no loop to iterate. Written inside a bare if with no enclosing loop, it is a compile-time error.

Q: Point out the error, if any in the program. #include <stdio.h> int main() { int a = 10; switch(a) { } printf("This is c program."); return 0; }

Correct answer: No ErrorA switch body is just a compound statement, and an empty one is perfectly legal. Neither a case nor a default is required - the switch simply evaluates its controlling expression, finds no matching label, and does nothing. The program compiles and prints its message.

Q: In C++, which system - provided function is called when no handler is provided to deal with an exception?

Correct answer: terminate ( )If an exception is thrown and no matching handler is found, C++ calls std::terminate(), which by default calls abort(). unexpected() belonged to the old dynamic exception specifications and is now removed; abort() is what terminate ends up calling rather than the function called first.

91.

If scanf() is used to store a value in a char variable then along with the value a carriage return also gets stored with it.

A.True
B.False

Answer: B

Correct answer: False

Nothing extra is stored. scanf("%c", &ch) reads exactly one character into the variable; the newline you typed afterwards is simply left in the input buffer, where it will be picked up by the next read. That is why a second %c so often appears to read nothing - it consumes the leftover newline.

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92.

What will be the output of the program?

#include <stdio.h>
int main()
{
    int x=1, y=1;
    for(; y; printf("%d %d\n", x, y))
    {
        y = x++ <= 5;
    }
    printf("\n");
    return 0;
}

A.2 13 14 15 16 17 0
B.2 13 14 15 16 1
C.2 13 14 15 1
D.2 23 34 45 5

Answer: A

Correct answer: 2 1 3 1 4 1 5 1 6 1 7 0

The third clause of the for is the printf, so the values are printed after each pass through the body. The body sets y to the result of x++ <= 5, which is 1 while the old x is at most 5. So the pairs printed are 2 1, 3 1, 4 1, 5 1, 6 1 - and on the pass where x is 6 the comparison fails, giving 7 0, after which the condition y is false and the loop ends.

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93.

A do-while loop terminates when its controlling expression evaluates to

A.One
B.Zero
C.Non - zero
D.None of the above

Answer: B

Correct answer: Zero

A loop continues while its condition is true, that is non-zero, and stops when it evaluates to zero. The do-while differs from the others only in when the test happens - after the body rather than before - so the body always runs at least once.

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94.

#include <stdio.h>
int main()
{
    int i;
    if (printf("0"))
        i = 3;
    else
        i = 5;
    printf("%d", i);
    return 0;
}

A.3
B.5
C.03
D.05

Answer: C

Correct answer: 03

printf returns the number of characters written. It prints 0 - that is one character - and returns 1, which is true, so i becomes 3. The output is therefore the 0 from the condition followed by the 3: 03.

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95.

What will be the output of the program?

#include <stdio.h>
int main()
{
    int a = 300, b, c;
    if(a >= 400)
        b = 300;
    c = 200;
    printf("%d, %d, %d\n", a, b, c);
    return 0;
}

A.300, 300, 200
B.Garbage, 300, 200
C.300, Garbage, 200
D.300, 300, Garbage

Answer: C

Correct answer: 300, Garbage, 200

The condition \(300 \ge 400\) is false, so b = 300 never runs - and b, an uninitialised automatic variable, holds whatever was on the stack. c = 200 is a separate statement outside the if, so it always executes.

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96.

What will be the output of the program?

#include <stdio.h>
int main()
{
    int i=3;
    switch(i)
    {
        case 1:
            printf("Hello\n");
        case 2:
            printf("Hi\n");
        case 3:
            continue;
        default:
            printf("Bye\n");
    }
    return 0;
}

A.Error: Misplaced continue
B.Bye
C.No output
D.Hello Hi

Answer: A

Correct answer: Error: Misplaced continue

continue asks for the next iteration of a loop, and a switch is not a loop - nor is there any loop around this one. The compiler therefore rejects it. break would have been legal, since break applies to a switch as well as to a loop.

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97.

Point out the error, if any in the program.

#include <stdio.h>
int main()
{
    int i = 1;
    switch(i)
    {
        printf("This is c program.");
        case 1:
            printf("Case1");
            break;
        case 2:
            printf("Case2");
            break;
    }
return 0;
}

A.Error: No default specified
B.Error: Invalid printf statement after switch statement
C.No Error and prints "Case1"
D.None of above

Answer: C

Correct answer: No Error and prints "Case1"

The printf before the first case is legal but unreachable: a switch transfers control straight to a matching label, so nothing before the first label ever runs. i is 1, so case 1 executes and the break ends the switch.

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98.

What is the output of this C code?

void main()

    {

        int i = 0;

        if (i == 0)

        {

            printf("Hello");

            continue;

        }

    }

A.Hello is printed infinite times
B.Hello
C.varies
D.Compile time error

Answer: D

Correct answer: Compile time error

continue is meaningful only inside a loop: it asks for the next iteration, and here there is no loop to iterate. Written inside a bare if with no enclosing loop, it is a compile-time error.

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99.

Point out the error, if any in the program.

#include <stdio.h>
int main()
{
    int a = 10;
    switch(a)
    {
    }
    printf("This is c program.");
    return 0;
}

A.Error: No case statement specified
B.Error: No default specified
C.No Error
D.Error: infinite loop occurs

Answer: C

Correct answer: No Error

A switch body is just a compound statement, and an empty one is perfectly legal. Neither a case nor a default is required - the switch simply evaluates its controlling expression, finds no matching label, and does nothing. The program compiles and prints its message.

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100.

In C++, which system - provided function is called when no handler is provided to deal with an exception?

A.terminate ( )
B.unexpected ( )
C.abort ( )
D.kill ( )

Answer: A

Correct answer: terminate ( )

If an exception is thrown and no matching handler is found, C++ calls std::terminate(), which by default calls abort(). unexpected() belonged to the old dynamic exception specifications and is now removed; abort() is what terminate ends up calling rather than the function called first.

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