Which of the following is correct with respect to “Jump Statements” in C?
Answer: D
Correct answer: All of the above.
C has four jump statements, and three of them are listed: goto, which transfers to a label in the same function; continue, which starts the next iteration; and break, which leaves a loop or switch. The fourth is return.
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Which of the following sentences are correct about a switch loop in a C program?
1. switch is useful when we wish to check the value of variable against a particular set of values.
2. switch is useful when we wish to check whether a value falls in different ranges.
3. Compiler implements a jump table for cases used in switch.
4. It is not necessary to use a break in every switch statement.
Answer: B
Correct answer: 1,3,4
1 is true - a switch compares the controlling expression against a set of discrete constants. 3 is true: where the labels are dense the compiler typically builds a jump table, which is why a switch can beat a chain of ifs. 4 is true: omitting break is legal and produces deliberate fall-through.
2 is false. A switch cannot test a range - each value in the range needs its own label - which is what if-else if is for.
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Consider the following pseudocode:
x:=1;
i:=1;
while (x ≤ 500)
begin
x := 2^x ;
i:=i+1;
end
What is the value of i at the end of the pseudocode?
Answer: B
Correct answer: 5
Each pass replaces x by \(2^x\), which grows extremely fast:
| after pass | - | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| x | 1 | 2 | 4 | 16 | 65536 |
| i | 1 | 2 | 3 | 4 | 5 |
The test \(x \le 500\) fails once x reaches 65536, and i is then 5.
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In mathematics and computer programming, which is the correct order of mathematical operators ?
Answer: B
Correct answer: Division, Multiplication, Addition, Subtraction
Multiplication and division sit at the same, higher precedence, and addition and subtraction at the same, lower one; within a level, evaluation runs left to right. The listed order reflects that grouping, which is what BODMAS and PEMDAS describe.
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What will be the output of the program?
#include <stdio.h>
int main()
{
int i = 5;
while(i-- >= 0)
printf("%d,", i);
i = 5;
printf("\n");
while(i-- >= 0)
printf("%i,", i);
while(i-- >= 0)
printf("%d,", i);
return 0;
}
Answer: A
Correct answer: 4, 3, 2, 1, 0, -1 4, 3, 2, 1, 0, -1
i-- >= 0 tests the old value and then decrements, so the value printed is always one less than the value tested. Starting at 5 that gives 4, 3, 2, 1, 0 and finally -1 - the pass where the test saw 0. The loop then leaves i at -2. After i is reset to 5 the second loop prints the same line. The third loop then starts with i at -2, so its very first test fails and it prints nothing.
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Which of the following cannot be checked in a switch-case statement?
Answer: C
Correct answer: Float
A switch requires an integer controlling expression, so char, int and enumeration constants are all fine. float is not: exact equality against a case label would be unreliable for values that cannot be represented exactly in binary.
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How many times the while loop will get executed if a short int is 2 byte wide?
#include <stdio.h>
int main()
{
int j=1;
while(j <= 255)
{
printf("%c %d\n", j, j);
j++;
}
return 0;
}
Answer: B
Correct answer: 255 times
j runs from 1 and the loop continues while j <= 255, so it executes for j equal to 1, 2, …, 255 - 255 passes. The width of a short is a red herring: j is declared int, and 255 is nowhere near the limit of either type.
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What is the output of this C code?
void main()
{
int k;
for (k = -3; k < -5; k++)
printf("Hello");
}
Answer: D
Correct answer: Nothing
A for tests its condition before the first pass. With k at -3, the test k < -5 is already false, so the body never runs and nothing is printed. (Had it been a do-while, the body would have run once.)
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What is the output of the following C code?
#include <stdio.h>
int main()
{
int index;
for(index=1; index<=5; index++)
{
printf("%d", index);
if (index==3)
continue;
}
}
Answer: B
Correct answer: 12345
The continue is the last statement in the body, so it skips nothing - the next thing after it would have been the end of the iteration anyway. Every pass prints its index, giving 12345.
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A char variable can store either an ASCII character or a Unicode character.
Answer: A
Correct answer: False
In C a char is one byte - sizeof(char) is 1 by definition - and on ordinary implementations that is eight bits, giving 256 possible values. That is ample for ASCII, which uses only the codes 0 to 127, but Unicode defines over a million code points, so a single char cannot hold an arbitrary Unicode character. C provides other types for that work: wchar_t for wide characters, and since C11 char16_t and char32_t for UTF-16 and UTF-32 code units, declared in <uchar.h>. What a char array can hold is a Unicode character encoded in UTF-8, but that takes one to four char elements per character, not one - the character is spread across several bytes rather than stored in a single variable. The confusion usually comes from Java, where char is a 16-bit UTF-16 code unit and the statement would be much closer to true. In C it is false.
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