Control Instructions Questions and Answers

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.

Q: The statement c = (n) ? a : b; can be rewritten as

Correct answer: if(n){c = a;}else{c = b;}The conditional operator evaluates its first operand as a condition: if it is true the result is the second operand, otherwise the third. So c = n ? a : b; assigns a when n is non-zero and b when it is zero - exactly what the first if-else does.

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: #include <stdio.h> int main() { int i = 3; while (i--) { int i = 100; i--; printf("%d ", i); } return 0; }

Correct answer: 99 99 99The inner int i = 100; shadows the outer i for the whole of the loop body, so i-- and the printf refer to the new variable, which is created afresh at 100 on every pass and printed as 99. The outer i is untouched inside the body and is decremented only by the while condition, so the loop still runs three times.

Q: What is the output of this C code? int main() { printf("before continue "); continue; printf("after continue\n"); }

Correct answer: Compile time errorcontinue must appear inside a loop. In a function body with no loop around it there is no next iteration to jump to, so the compiler rejects the program - neither printf ever runs.

101.

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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102.

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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103.

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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104.

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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105.

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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106.

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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107.

The statement c = (n) ? a : b; can be rewritten as

A.if(n){c = a;}else{c = b;}
B.if(!n){c = a;}else{c = b;}
C.if(n){c = b;}else{c = a;}
D.None of the above

Answer: A

Correct answer: if(n){c = a;}else{c = b;}

The conditional operator evaluates its first operand as a condition: if it is true the result is the second operand, otherwise the third. So c = n ? a : b; assigns a when n is non-zero and b when it is zero - exactly what the first if-else does.

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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.

#include <stdio.h>
int main()
{
    int i = 3;
    while (i--)
    {
        int i = 100;
        i--;
        printf("%d ", i);
    }
    return 0;
}

A.Infinite Loop
B.99 99 99
C.99 98 97
D.2 2 2

Answer: B

Correct answer: 99 99 99

The inner int i = 100; shadows the outer i for the whole of the loop body, so i-- and the printf refer to the new variable, which is created afresh at 100 on every pass and printed as 99. The outer i is untouched inside the body and is decremented only by the while condition, so the loop still runs three times.

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110.

What is the output of this C code?

int main()

    {

        printf("before continue ");

        continue;

        printf("after continue\n");

    }

A.Before continue after continue
B.Before continue
C.after continue
D.Compile time error

Answer: D

Correct answer: Compile time error

continue must appear inside a loop. In a function body with no loop around it there is no next iteration to jump to, so the compiler rejects the program - neither printf ever runs.

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