Declarations - C Multiple Choice Questions and Answers

1. What is the output of this C code?

void foo(const int *);
int main()
{
const int i = 10;
printf("%d ", i);
foo(&i);
printf("%d", i);
}
void foo(const int *i)
{
*i = 20;
}

A. Compile time error
B. 10 20
C. Undefined value
D. 10

Answer & Explanation

Answer: Option A

Explanation:

Cannot change a const type value.
Output:
$ cc pgm1.c
pgm1.c: In function ‘foo’:
pgm1.c:13: error: assignment of read-only location ‘*i’

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2. Comment on the output of this C code?

int main()
{
const int i = 10;
int *ptr = &i;
*ptr = 20;
printf("%d\n", i);
return 0;
}

A. Compile time error
B. Compile time warning and printf displays 20
C. Undefined behaviour
D. 10

Changing const variable through non-constant pointers invokes compiler warning
Output:
$ cc pgm2.c
pgm2.c: In function ‘main’:
pgm2.c:5: warning: initialization discards qualifiers from pointer target type
$ a.out
20

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3. What is the output of this C code?

int main()
{
j = 10;
printf("%d\n", j++);
return 0;
}

A. 10
B. 11
C. Compile time error
D. 0

Answer & Explanation

Answer: Option C

Explanation:

Variable j is not defined.
Output:
$ cc pgm3.c
pgm3.c: In function ‘main’:
pgm3.c:4: error: ‘j’ undeclared (first use in this function)
pgm3.c:4: error: (Each undeclared identifier is reported only once
pgm3.c:4: error: for each function it appears in.)

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4. Does this compile without error?

int main()
{
for (int k = 0; k < 10; k++);
return 0;
}

A. Yes
B. No
C. Depends on the C standard implemented by compilers
D. None of the mentioned

Answer & Explanation

Answer: Option C

Explanation:

Compilers implementing C90 does not allow this but compilers implementing C99 allow it.
Output:
$ cc pgm4.c
pgm4.c: In function ‘main’:
pgm4.c:4: error: ‘for’ loop initial declarations are only allowed in C99 mode
pgm4.c:4: note: use option -std=c99 or -std=gnu99 to compile your code

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5. Does this compile without error?

int main()
{
int k;
{
int k;
for (k = 0; k < 10; k++);
}
}

A. Yes
B. No
C. Depends on the compiler
D. Depends on the C standard implemented by compilers

Answer & Explanation

Answer: Option A

Explanation:

There can be blocks inside block and within blocks variables have only block scope.
Output:
$ cc pgm5.c

Online Test Name	Declarations
Exam Type	Multiple Choice Questions
Category	Computer Science Engineering Quiz
Number of Questions	14

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