Control Instructions Questions and Answers

Q: Consider the following program fragment i=6720; j=4; while (i%j)==0 { i=i/j; j=j+1; } On termination j will have the value

Correct answer: 9Each pass divides i by j and then increases j:i672016803365681j456789At each step the division is exact, so the loop continues - until i is 1 and j is 9, where \(1 \bmod 9 = 1\) and the loop stops. j is then 9. (Note that 6720 = 4 × 5 × 6 × 7 × 8, which is what makes every division exact.)

Q: Which of the following statements are correct about the below program? #include <stdio.h> int main() { int i = 10, j = 15; if(i % 2 = j % 3) printf("IndiaBIX\n"); return 0; }

Correct answer: Error: Lvalue required= is assignment, not comparison, and its left operand must be an object that can be assigned to. i % 2 is a computed value, so the compiler reports that an lvalue is required. The author meant ==.

Q: How many times is GeeksQuiz printed? #include <stdio.h> int main() { int i = -5; while (i <= 5) { if (i >= 0) break; else { i++; continue; } printf("GeeksQuiz"); } return 0; }

Correct answer: 0 timesEvery path through the loop body reaches either break or continue before the printf. While i is negative the else runs, incrementing and continuing; the moment i reaches 0 the break fires. The printf is therefore unreachable, and a compiler will usually say so.

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

Correct answer: HiA switch jumps directly to a matching label, so the printf("Hello") written before any case is unreachable. i is 1, so control lands on case 1, prints Hi, and the break ends the switch.

Q: When 1 is entered, The output of the code below is? #include <stdio.h> void main() { int ch; printf("enter a value btw 1 to 2:"); scanf("%d", &ch); switch (ch, ch + 1) { case 1: printf("1\n"); break; case 2: printf("2"); break; } }

Correct answer: 2The controlling expression uses the comma operator: ch, ch + 1 evaluates ch, discards it, and yields ch + 1. With 1 entered, the switch is therefore performed on 2, so case 2 runs and prints 2.

Q: Which of the following statements are correct about the below program? #include <stdio.h> int main() { int i = 0; i++; if(i <= 5) { printf("IndiaBIX\n"); exit(0); main(); } return 0; }

Correct answer: The program prints 'IndiaBIX' one timeexit(0) terminates the program immediately. The recursive main() call written after it is never reached, so the message is printed exactly once. (Calling main recursively is legal in C, which is why the last option is wrong - it just never happens here.)

Q: Can we use a switch statement to switch on strings?

Correct answer: NoA switch requires an integer controlling expression, and a string in C is an array of characters - in an expression, a pointer. Comparing strings means comparing their contents, which == does not do, so a chain of if (strcmp(s, "...") == 0) is the usual alternative. (Java added string switches; C has not.)

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.

61.

Consider the following program fragment i=6720; j=4; while (i%j)==0 { i=i/j; j=j+1; } On termination j will have the value

A.4
B.8
C.9
D.6720

Answer: C

Correct answer: 9

Each pass divides i by j and then increases j:

i	6720	1680	336	56	8	1
j	4	5	6	7	8	9

At each step the division is exact, so the loop continues - until i is 1 and j is 9, where \(1 \bmod 9 = 1\) and the loop stops. j is then 9. (Note that 6720 = 4 × 5 × 6 × 7 × 8, which is what makes every division exact.)

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62.

In the context of "break" and "continue" statements in C, pick the best statement.

A.“break” can be used in “for”, “while” and “do-while” loop body.
B.“continue” can be used in “for”, “while” and “do-while” loop body
C.“break” and “continue” can be used in “for”, “while”, “do-while” loop body and “switch” body
D.“break” and “continue” can be used in “for”, “while” and “do-while” loop body. But only “break” can be used in “switch” body

Answer: D

Correct answer: “break” and “continue” can be used in “for”, “while” and “do-while” loop body. But only “break” can be used in “switch” body

Both statements work in all three loops. The difference is the switch: break is what ends a switch, while continue has no meaning there, since a switch has no iterations. A continue written inside a switch applies to the loop enclosing the switch, and fails to compile if there is none.

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63.

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

#include <stdio.h>
int main()
{
    int i = 10, j = 15;
    if(i % 2 = j % 3)
        printf("IndiaBIX\n");
    return 0;
}

A.Error: Expression syntax
B.Error: Lvalue required
C.Error: Rvalue required
D.The Code runs successfully

Answer: B

Correct answer: Error: Lvalue required

= is assignment, not comparison, and its left operand must be an object that can be assigned to. i % 2 is a computed value, so the compiler reports that an lvalue is required. The author meant ==.

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64.

How many times is GeeksQuiz printed?

#include <stdio.h>
int main()
{
    int i = -5;
    while (i <= 5)
    {
        if (i >= 0)
            break;
        else
        {
            i++;
            continue;
        }
        printf("GeeksQuiz");
    }
    return 0;
}

A.10 times
B.5 times
C.Infinite times
D.0 times

Answer: D

Correct answer: 0 times

Every path through the loop body reaches either break or continue before the printf. While i is negative the else runs, incrementing and continuing; the moment i reaches 0 the break fires. The printf is therefore unreachable, and a compiler will usually say so.

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65.

What will be the output of the program?

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

A.HelloHi
B.HelloBye
C.Hi
D.Bye

Answer: C

Correct answer: Hi

A switch jumps directly to a matching label, so the printf("Hello") written before any case is unreachable. i is 1, so control lands on case 1, prints Hi, and the break ends the switch.

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66.

When 1 is entered, The output of the code below is?

#include <stdio.h>
    void main()
    {
        int ch;
        printf("enter a value btw 1 to 2:");
        scanf("%d", &ch);
        switch (ch, ch + 1)
        {
        case 1:
            printf("1\n");
            break;
        case 2:
            printf("2");
            break;
        }
    }

A.1
B.2
C.3
D.Run time error

Answer: B

Correct answer: 2

The controlling expression uses the comma operator: ch, ch + 1 evaluates ch, discards it, and yields ch + 1. With 1 entered, the switch is therefore performed on 2, so case 2 runs and prints 2.

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67.

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

#include <stdio.h>
int main()
{
    int i = 0;
    i++;
    if(i <= 5)
    {
        printf("IndiaBIX\n");
        exit(0);
        main();
    }
    return 0;
}

A.The program prints 'IndiaBIX' 5 times
B.The program prints 'IndiaBIX' one time
C.The call to main() after exit() doesn't materialize.
D.The compiler reports an error since main() cannot call itself.

Answer: B

Correct answer: The program prints 'IndiaBIX' one time

exit(0) terminates the program immediately. The recursive main() call written after it is never reached, so the message is printed exactly once. (Calling main recursively is legal in C, which is why the last option is wrong - it just never happens here.)

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68.

Can we use a switch statement to switch on strings?

A.Yes
B.No

Answer: B

Correct answer: No

A switch requires an integer controlling expression, and a string in C is an array of characters - in an expression, a pointer. Comparing strings means comparing their contents, which == does not do, so a chain of if (strcmp(s, "...") == 0) is the usual alternative. (Java added string switches; C has not.)

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69.

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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70.

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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