Control Instructions Questions and Answers

Q: What will be the output of the program? #include <stdio.h> int main() { float a = 0.7; if(0.7 > a) printf("Hi\n"); else printf("Hello\n"); return 0; }

Correct answer: Hi0.7 written in the source is a double, while a is a float, which holds fewer bits. Storing 0.7 in a float loses precision, and when a is promoted back to double for the comparison it is slightly less than the double 0.7. So the condition is true and Hi is printed - the classic warning against comparing floating-point values of different types for equality or order.

Q: Which of the following is not a logical operator?

Correct answer: && is the bitwise AND: it combines the operands bit by bit and yields an integer. The logical operators are &&, || and !, which treat their operands as true or false, yield 0 or 1, and - unlike & - short-circuit.

Q: Which of the following sentences are correct about a for loop in a C program? 1. for loop works faster than a while loop. 2. All things that can be done using a for loop can also be done using a while loop 3. for(;;); implements an infinite loop. 4. for loop can be used if we want statements in a loop get executed at least once.

Correct answer: 2, 3, 42 is true - anything a for can do a while can do, since the for is only a compact way of writing initialisation, test and update. 3 is true: an omitted condition counts as true, so for(;;) loops forever.1 is false. Both compile to the same test-at-the-top loop, so neither is faster.4 is the weakest of the four: the construct designed to run its body at least once is the do-while, though a for can of course be written so that its condition is true on the first test.

Q: What is the output of this C code? void main() { int i = 0, j = 0; for (i = 0;i < 5; i++) { for (j = 0;j < 4; j++) { if (i > 1) break; } printf("Hi \n"); } }

Correct answer: Hi is printed 5 timesThe printf is outside the inner loop but inside the outer one, so it runs once per outer iteration - five times in all. The break only ever escapes the inner loop, and even then it changes nothing visible: whether the inner loop runs four times or stops at once, the outer loop still completes its five passes.

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

Correct answer: Compile time errorA switch requires an integer controlling expression, and ch is a double. Floating-point values are excluded precisely because equality against a case label would be unreliable for numbers that cannot be represented exactly in binary.

Q: Which of the following is an invalid if-else statement?

Correct answer: if (if (a == 1)){}An if is a statement, and the parentheses of an if must contain an expression - so an if cannot appear there. The other three are fine: any scalar expression will do as a condition, including a cast and a function call.

Q: What will be the output of the program? #include <stdio.h> int main() { unsigned int i = 65536; /* Assume 2 byte integer*/ while(i != 0) printf("%d",++i); printf("\n"); return 0; }

Correct answer: No outputAn unsigned int two bytes wide holds 0 to 65535, so the initialiser 65536 wraps round to 0. The condition i != 0 is false on the very first test, the loop body never runs, and the only thing printed is the newline.

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.

91.

What will be the output of the program?

#include <stdio.h>
int main()
{
    float a = 0.7;
    if(0.7 > a)
        printf("Hi\n");
    else
        printf("Hello\n");
    return 0;
}

A.Hi
B.Hello
C.Hi Hello
D.None of above

Answer: A

Correct answer: Hi

0.7 written in the source is a double, while a is a float, which holds fewer bits. Storing 0.7 in a float loses precision, and when a is promoted back to double for the comparison it is slightly less than the double 0.7. So the condition is true and Hi is printed - the classic warning against comparing floating-point values of different types for equality or order.

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92.

Which of the following is not a logical operator?

A.&
B.&&
C.||
D.!

Answer: A

Correct answer: &

& is the bitwise AND: it combines the operands bit by bit and yields an integer. The logical operators are &&, || and !, which treat their operands as true or false, yield 0 or 1, and - unlike & - short-circuit.

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93.

Which of the following sentences are correct about a for loop in a C program?

1. for loop works faster than a while loop.

2. All things that can be done using a for loop can also be done using a while loop

3. for(;;); implements an infinite loop.

4. for loop can be used if we want statements in a loop get executed at least once.

A.1
B.1, 2
C.2, 3
D.2, 3, 4

Answer: D

Correct answer: 2, 3, 4

2 is true - anything a for can do a while can do, since the for is only a compact way of writing initialisation, test and update. 3 is true: an omitted condition counts as true, so for(;;) loops forever.

1 is false. Both compile to the same test-at-the-top loop, so neither is faster.

4 is the weakest of the four: the construct designed to run its body at least once is the do-while, though a for can of course be written so that its condition is true on the first test.

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94.

What is the output of this C code?

void main()

    {

        int i = 0, j = 0;

        for (i = 0;i < 5; i++)

        {

            for (j = 0;j < 4; j++)

            {

                if (i > 1)

                    break;

            }

            printf("Hi \n");

        }

    }

A.Hi is printed 5 times
B.Hi is printed 9 times
C.Hi is printed 7 times
D.Hi is printed 4 times

Answer: A

Correct answer: Hi is printed 5 times

The printf is outside the inner loop but inside the outer one, so it runs once per outer iteration - five times in all. The break only ever escapes the inner loop, and even then it changes nothing visible: whether the inner loop runs four times or stops at once, the outer loop still completes its five passes.

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95.

The output of the code below is

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

A.Compile time error
B.1
C.2
D.Varies

Answer: A

Correct answer: Compile time error

A switch requires an integer controlling expression, and ch is a double. Floating-point values are excluded precisely because equality against a case label would be unreliable for numbers that cannot be represented exactly in binary.

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96.

Which of the following is an invalid if-else statement?

A.if (if (a == 1)){}
B.if (a){}
C.if ((char) a){}
D.if (func1 (a)){}

Answer: A

Correct answer: if (if (a == 1)){}

An if is a statement, and the parentheses of an if must contain an expression - so an if cannot appear there. The other three are fine: any scalar expression will do as a condition, including a cast and a function call.

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97.

What will be the output of the program?

#include <stdio.h>
int main()
{
    unsigned int i = 65536; /* Assume 2 byte integer*/
    while(i != 0)
        printf("%d",++i);
    printf("\n");
    return 0;
}

A.Infinite loop
B.0 1 2 ... 65535
C.0 1 2 ... 32767 - 32766 -32765 -1 0
D.No output

Answer: D

Correct answer: No output

An unsigned int two bytes wide holds 0 to 65535, so the initialiser 65536 wraps round to 0. The condition i != 0 is false on the very first test, the loop body never runs, and the only thing printed is the newline.

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98.

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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99.

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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100.

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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