Control Instructions Questions and Answers

Q: How many lines of output does the following C code produce? #include <stdio.h> float i=2.0; float j=1.0; float sum = 0.0; main() { while (i/j > 0.001) { j+=j; sum=sum+(i/j); printf("%f\n", sum); } }

Correct answer: 11Each pass doubles j and prints, so the tested quantity \(i/j\) starts at 2 and halves every time: 2, 1, 0.5, 0.25, … The loop continues while it exceeds 0.001. Since \(2/2^{11} = 0.000977\) is the first value at or below the threshold, the test succeeds for \(j = 1, 2, 4, \ldots, 1024\) - eleven passes, and eleven lines.

Q: Point out the error, if any in the for loop. #include <stdio.h> int main() { int i=1; for(;;) { printf("%d\n", i++); if(i>10) break; } return 0; }

Correct answer: No errorfor(;;) is legal and idiomatic: all three clauses may be omitted, and an omitted condition is taken as true, giving an infinite loop. The two semicolons are required, since the header always has three parts. The loop here terminates properly through its break.

Q: What will be the output of the program? #include <stdio.h> int main() { char str[]="C-program"; int a = 5; printf(a >10?"Ps\n":"%s\n", str); return 0; }

Correct answer: C-programThe conditional operator chooses between the two format strings, not between two outputs. Since \(5 > 10\) is false, the format used is "%s\n", and str is the argument it consumes - so the program prints C-program. Had the condition been true, "Ps\n" would have been the format and str an unused extra argument.

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: Which of the following errors would be reported by the compiler on compiling the program given below? #include <stdio.h> int main() { int a = 5; switch(a) { case 1: printf("First"); case 2: printf("Second"); case 3 + 2: printf("Third"); case 5: printf("Final"); break; } return 0; }

Correct answer: Duplicate case case 5:case 3 + 2 is perfectly legal - a label may be any constant expression, and the compiler evaluates it to 5. That is exactly the problem: it then collides with case 5, and duplicate labels are an error, since the jump would be ambiguous. Missing break statements are legal (they produce fall-through).

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: Which of the following statements are correct about the below program? #include <stdio.h> int main() { int n = 0, y = 1; y == 1 ? n=0 : n=1; if(n) printf("Yes\n"); else printf("No\n"); return 0; }

Correct answer: Error: Lvalue requiredAssignment binds more loosely than ?:, so the line parses as (y == 1 ? n = 0 : n) = 1;, and the left-hand side is a value rather than an object. The compiler reports that an lvalue is required. Written as n = (y == 1) ? 0 : 1; it compiles and does what was meant.

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: The output of the code below is #include <stdio.h> int x; void main() { if (x) printf("hi"); else printf("how are u"); }

Correct answer: how are ux is declared at file scope, so it has static storage duration and is zero-initialised - not left holding junk, as an uninitialised local would be. The condition is therefore false and the else branch runs.

Q: What will be the output of the program? #include <stdio.h> int main() { int a = 500, b = 100, c; if(!a >= 400) b = 300; c = 200; printf("b = %d c = %d\n", b, c); return 0; }

Correct answer: b = 100 c = 200! binds far tighter than >=, so the condition is (!a) >= 400, not !(a >= 400). With a non-zero, !a is 0, and \(0 \ge 400\) is false - so b keeps its initial 100. The assignment c = 200 is a separate statement, outside the if altogether, so it always runs.

61.

How many lines of output does the following C code produce?

#include <stdio.h>
float i=2.0;
float j=1.0;
float sum = 0.0;
main()
{
    while (i/j > 0.001)
    {
        j+=j;
        sum=sum+(i/j);
        printf("%f\n", sum);
    }
}

A.8
B.9
C.10
D.11

Answer: D

Correct answer: 11

Each pass doubles j and prints, so the tested quantity \(i/j\) starts at 2 and halves every time: 2, 1, 0.5, 0.25, … The loop continues while it exceeds 0.001. Since \(2/2^{11} = 0.000977\) is the first value at or below the threshold, the test succeeds for \(j = 1, 2, 4, \ldots, 1024\) - eleven passes, and eleven lines.

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62.

Point out the error, if any in the for loop.

#include <stdio.h>
int main()
{
    int i=1;
    for(;;)
    {
        printf("%d\n", i++);
        if(i>10)
           break;
    }
    return 0;
}

A.There should be a condition in the for loop
B.The two semicolons should be dropped
C.The for loop should be replaced with while loop.
D.No error

Answer: D

Correct answer: No error

for(;;) is legal and idiomatic: all three clauses may be omitted, and an omitted condition is taken as true, giving an infinite loop. The two semicolons are required, since the header always has three parts. The loop here terminates properly through its break.

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63.

What will be the output of the program?

#include <stdio.h>
int main()
{
    char str[]="C-program";
    int a = 5;
    printf(a >10?"Ps\n":"%s\n", str);
    return 0;
}

A.C-program
B.Ps
C.Error
D.None of above

Answer: A

Correct answer: C-program

The conditional operator chooses between the two format strings, not between two outputs. Since \(5 > 10\) is false, the format used is "%s\n", and str is the argument it consumes - so the program prints C-program. Had the condition been true, "Ps\n" would have been the format and str an unused extra argument.

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64.

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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65.

Which of the following errors would be reported by the compiler on compiling the program given below?

#include <stdio.h>
int main()
{
    int a = 5;
    switch(a)
    {
    case 1:
    printf("First");

    case 2:
    printf("Second");

    case 3 + 2:
    printf("Third");

    case 5:
    printf("Final");
    break;

    }
    return 0;
}

A.There is no break statement in each case.
B.Expression as in case 3 + 2 is not allowed.
C.Duplicate case case 5:
D.No error will be reported

Answer: C

Correct answer: Duplicate case case 5:

case 3 + 2 is perfectly legal - a label may be any constant expression, and the compiler evaluates it to 5. That is exactly the problem: it then collides with case 5, and duplicate labels are an error, since the jump would be ambiguous. Missing break statements are legal (they produce fall-through).

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66.

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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67.

Which of the following statements are correct about the below program?

#include <stdio.h>
int main()
{
    int n = 0, y = 1;
    y == 1 ? n=0 : n=1;
    if(n)
        printf("Yes\n");
    else
        printf("No\n");
    return 0;
}

A.Error: Declaration terminated incorrectly
B.Error: Syntax error
C.Error: Lvalue required
D.None of above

Answer: C

Correct answer: Error: Lvalue required

Assignment binds more loosely than ?:, so the line parses as (y == 1 ? n = 0 : n) = 1;, and the left-hand side is a value rather than an object. The compiler reports that an lvalue is required. Written as n = (y == 1) ? 0 : 1; it compiles and does what was meant.

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68.

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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69.

The output of the code below is

#include <stdio.h>
    int x;
    void main()
    {
        if (x)
            printf("hi");
        else
            printf("how are u");
    }

A.hi
B.how are u
C.compile time error
D.none of the mentioned

Answer: B

Correct answer: how are u

x is declared at file scope, so it has static storage duration and is zero-initialised - not left holding junk, as an uninitialised local would be. The condition is therefore false and the else branch runs.

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70.

What will be the output of the program?

#include <stdio.h>
int main()
{
    int a = 500, b = 100, c;
    if(!a >= 400)
        b = 300;
    c = 200;
    printf("b = %d c = %d\n", b, c);
    return 0;
}

A.b = 300 c = 200
B.b = 100 c = garbage
C.b = 300 c = garbage
D.b = 100 c = 200

Answer: D

Correct answer: b = 100 c = 200

! binds far tighter than >=, so the condition is (!a) >= 400, not !(a >= 400). With a non-zero, !a is 0, and \(0 \ge 400\) is false - so b keeps its initial 100. The assignment c = 200 is a separate statement, outside the if altogether, so it always runs.

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