What is the value of x in this C code?
void main()
{
int x = 4 *5 / 2 + 9;
}
Answer: C
Correct answer: 19
* and / bind tighter than + and, having equal precedence, associate left to right:
Every step is integer arithmetic, so the answer is exactly 19.
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What will be the output of the following code?
#include <stdio.h>
int main()
{
extern int a;
static char j = 'E';
printf("%c %d", ++j, ++a);
return 0;
}
Answer: B
Correct answer: F 1
++j takes the static char from 'E' to 'F', which %c prints as the letter. extern int a; declares a variable defined at file scope elsewhere; such an object has static storage duration and is therefore zero-initialised, so ++a gives 1. Output: F 1.
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What is the output of this C code?
void main()
{
int x = 4, y, z;
y = --x;
z = x--;
printf("%d%d%d", x, y, z);
}
Answer: B
Correct answer: 2 3 3
Follow the two statements:
y = --x; - pre-decrement, so x becomes 3 and y takes that new value, 3.z = x--; - post-decrement, so z takes the old value 3 and x then becomes 2.Printing x, y, z gives 2 3 3.
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Which among the following is NOT a logical or relational operator?
Answer: D
Correct answer: =
= is the assignment operator: it stores a value rather than comparing or combining truth values. != and == are relational, and || is logical. Mistaking = for == in a condition is the classic C bug.
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What is the value of x after executing the following statement?
int x = 011 | 0x10;
Answer: C
Correct answer: 25
The two literals are in different bases: a leading 0 marks octal and 0x marks hexadecimal.
The bitwise OR sets every bit that is set in either, giving \(11001_2 = 25\).
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What is the output of this C code?
void main()
{
int a = 5, b = -7, c = 0, d;
d = ++a && ++b || ++c;
printf("\n%d%d%d%d", a, b, c, d);
}
Answer: D
Correct answer: 6 -6 0 1
Evaluate left to right, remembering that any non-zero value is true.
++a makes a 6, which is true.++b makes b -6 - non-zero, so also true.&& is therefore true, so || short-circuits and ++c never runs: c stays 0.d gets the value of the whole expression, 1.Output: 6 -6 0 1.
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Which is not a storage class?
Answer: B
Correct answer: Struct
The storage classes in C are auto, register, static, extern and typedef - typedef being grouped with them by the grammar even though it names a type rather than allocating storage. struct is not among them: it introduces a type, and a structure variable still needs a storage class of its own.
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For the following statement find the values generated for p and q?
int p = 0, q = 1;
p = q++;
p = ++q;
p = q--;
p = --q;
Value of p & q are
Answer: A
Correct answer: 1 1
Follow the four statements from p = 0, q = 1:
p = q++; - p gets the old 1; q becomes 2.p = ++q; - q becomes 3 and p gets 3.p = q--; - p gets the old 3; q becomes 2.p = --q; - q becomes 1 and p gets 1.So both end at 1.
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What is the output of this C code?
void main()
{
int a = -5;
int k = (a++, ++a);
printf("%d\n", k);
}
Answer: A
Correct answer: -3
The comma operator evaluates its left operand, discards the result, then evaluates the right operand and yields that. So a++ takes a to -4, then ++a takes it to -3 and produces -3. k is therefore -3. There is a sequence point at the comma, so this is well defined.
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What is the output of this C code?
int main()
{
int x = -2;
x = x >> 1;
printf("%d\n", x);
}
Answer: B
Correct answer: -1
-2 is all ones followed by a zero: \(\ldots 1110\). Shifting right on a signed negative value is an arithmetic shift in every mainstream implementation, so the sign bit is copied in from the left and the result is \(\ldots 1111 = -1\). Arithmetically it is a division by two, rounding toward negative infinity.
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