cquizzzz

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Question #1: What is the correct output from the following code?55% on 9917 times asked

#include

int main(int argc, char** argv){

int x = 3;printf("%d", x++ + ++x);return 1;

}

3

5

6

7

undefined - correct

description:If you modify a variable more than one time in a single statement the behavior isundefined according to the C standard.

Question #2: What will the following code do?66% on 4743 times asked

int main(int argc, char** argv){char* ptr = NULL;free(ptr);return 0;

}

core dump

nothing, but the code is safe - correct

undefined behavior

description:Calling free on a NULL ptr is a no operation. It is not illegal and will not coredump. It is defined behavior.

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Question #3: Which of the following differences between malloc and calloc are true? 53% on 4066 times asked

1) malloc allocates number of bytes passed as argument

2) calloc allocates the product of number of elementsmultiplied by the size of each element,which are both passed as arguments.

3) both malloc and calloc return void*

4) both malloc and calloc initialize allocatedmemory to all 0

1, 2, 3, 4

1, 2, 3 - correct

1, 2

1

none of the statements are true

description:All statements are true except 4. calloc will initialize the memory to 0, but mallocdoes not initialize the memory.

Question #4: True or false. Calling free on the same address twice is ok.60% on 3398 times asked

true

false - correct

description:False. You can not call free 2 times on the same address. This may core dump!

Question #5: Which are true about: void *realloc(void *ptr, size_t size);

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46% on 3336 times asked

1) realloc changes the size of the allocatedmemory pointed to by the argument ptr

2) newly allocated memory will be uninitialized

3) you can pass a NULL ptr safely to realloc

4) realloc will guarantee not to move the datapointed to in ptr

1, 2, 3, 4

1, 2, 3 - correct

1, 2

1

none are true

description:4 is false. realloc may move your data to a new pointer and free the memory atthe old pointer. It will return the new pointer, or the old pointer if the data is not moved.

Question #6: In general which of the following functions should be faster for sendinginformation to a file?53% on 3114 times asked

int printf(const char *format, ...);

int fprintf(FILE *stream, const char *format, ...);

ssize_t write(int fd, const void *buf, size_t count); - correct

description:In general, printf and fprintf should be slower than write. The printf functions areformatted printing and they have to be parsed where as write is the basic system call whichshould have less overhead.

Question #7: How many bytes of memory are used to store a long long data type?

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4 bytes

8 bytes

16 bytes

32 bytes

It is implementation defined - correct

description:The answer is different on different systems as per the C language specificationwhich allows this.

Question #8: What should the program below print?50% on 3588 times asked

#include #include #include void myfunc(char** param){

++param;}int main(){

char* string = (char*)malloc(64);strcpy(string, "hello_World");myfunc(&string);myfunc(&string);printf("%s\n", string);// ignore memory leak for sake of quizreturn 0;

}

hello_World - correct

ello_World

llo_World

lo_World

Illegal memory access, undefined behavior

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description:Look at it carefully, the function is not actually modifying the data from main, sothe original pointer is unchanged.

Question #9: In theory, which is faster, the call to strcpy or the call to memcpy?66% on 2479 times asked

#include #include int main(){

char msg[12] = "Hello World";char buffer1[12];char buffer2[12];

strcpy(buffer1, msg);memcpy(buffer2, msg, sizeof(msg));return 0;

}

strcpy

memcpy - correct

they should have the same speed

description:memcpy should be faster because it does not need to check every byte for aNULL, it is copying a known size of data.

Question #10: True or False?int32_t is a data type that is guaranteed to be available on all standard conforming Cimplementations and represents a 32 bit signed integer type? 61% on 2229 times asked

true

false - correct

description:This data type is a 32 bit signed integer and available in stdint.h. HOWEVER: Ifan implementation does not provide any integer type with 32 bit widths they do not have todefine this data type.

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Question #11: Which of the following is the correct way to declare a function pointernamed pMyFunc that returns an int and has an int parameter?52% on 3341 times asked

*(int pMyFunc(int));

int ()(int)* pMyFunc;

int (*pMyFunc)(int); - correct

int *pMyFunc (int);

(int *pMyFunc int);

Question #12: For the code below which lines should be reported as errors by acompiler?44% on 3663 times asked

int main(int argc, char** argv){

const char* foo = "wow"; // line 1foo = "top"; // line 2

foo[0] = 1; // line 3

return 0;}

line 2

line 3 - correct

lines 2 and 3

none of the lines

description:foo is a pointer to a const string. The pointer can be reassigned but the data inthe string can not. Had it been char *const foo; then it would have been a constant pointer tochangeable data.

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Question #13: When running the program below, the malloc statement will always beexecuted?58% on 1867 times asked

#include

int* ptrToData;

int main(){

if (!ptrToData){ptrToData = (int*)malloc(sizeof(int) * 10);

}

free(ptrToData);return 0;

}

True, the malloc statement will always be executed - correct

False, depending on how ptrToData is initialized in the machine the mallocstatement might not get run.

description:Variables declared outside of functions or with the static specifier are alwaysinitialized to zero. Therefore this program has deterministic behavior.

Question #14: What number is output by the program below? (assuming 8 bytepointers)46% on 2419 times asked

#include

int main(){const char firstname[] = "bobby";const char* lastname = "eraserhead";printf("%lu\n", sizeof(firstname) +

sizeof(lastname));

return 0;}

8

14 - correct

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16

17

20

description:6 bytes for the firstname array and 8 bytes for the pointer lastname.

Question #15: what value should be printed by the program:57% on 1784 times asked

typedef union ds_{

short s;char c;} ds;

ds object;object.s = 0x0503;printf("%d\n", object.c);

0

3

5

0x0503

machine dependent - correct

description:The answer is machine dependent. On a little endian machine, 3 should beprinted on a big endian machine 5 should be printed.

Question #16: What value gets printed by the program below?48% on 2085 times asked

struct Foo{int x:1;int y:2;

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};

struct Foo obj;

obj.x = 5;

printf("%d\n", obj.x);

1

2

5

not defined - correct

description:X is a 1 bit bitfield. Assigning 5 to it is not defined.

Question #17: What value gets printed by the program below?56% on 1970 times asked

int w = 3;int x = 31;int y = 10;double z = x / y % w;

printf("%f\n", z);

0 - correct

1

3

undefined

machine dependent

description:31 / 10 is integer division which ignores the remainder and gives result 3. 3modulus 3 has a result of 0.

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Question #18: What gets printed by the code below? (Assume 1 byte characters)70% on 1861 times asked

char array[] = "foo";

printf("%lu\n", sizeof(array[1]));

0

1 - correct

2

3

4

description:It prints the size of a single character which we are assuming to be 1 byte.

Question #19: What gets printed?59% on 1705 times asked

int array[2][2] = {0, 1, 2, 3};int i;int sum = 0;

for (i =0; i < 4; ++i){

int x, y;

x = i % 2;

if (x){y = 0;

}else{

y = 1;}sum += array[x][y];

}

printf("%d\n", sum);

6 - correct

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7

8

9

10

description:Note the order of initialization of the members of the array is array[0][0]=0,array[0][1]=1, array[1][0]=2, array[1][1]=3. And the addition done is SUM =array[0][1]+array[1][0]+array[0][1]+array[1][0]


int i = 3;

if (!i)i++;i++;

if (i==3)i+=2;i+=2;

printf("%d\n", i);

3

5

6 - correct

7

9

description:A single statement is part of an if conditional if no curly braces are used.

Question #21: What gets printed?

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printf("%d\n", 4 ?: 8);

4

0

8

NULL

program has a compiler error - correct

description:According to the C standard this program is invalid because it is missing an

expression between the ? and :. The interesting thing is that there is an extension to thewidely used GCC compiler that will make this code compile and the result will be 4. "Themiddle operand in a conditional expression may be omitted. Then if the first operand isnonzero, its value is the value of the conditional expression."

Question #22: what gets printed?45% on 1081 times asked

#include

int main(){

int ints[] = { 0, 1, 2, 3 };int* i1 = ints + 1;int a = ++*i1;int b = a + *i1;printf("%d\n", b);return 0;

}

3

4 - correct

5

6

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code has undefined behavior

description:the prefix operator and dereference operator have the same precedence andassociate from right to left


#include

int main(){

int ints[] = { 0, 5, 10, 15 };

int* i2 = ints + 2;int a = *i2++;printf("%d#%d\n", a, *i2);return 0;

}

10#11

10#15 - correct

11#15

15#15

ill-formed syntax

description:The postfix increment operator has priority over the dereference operator. In thiscase the increment is done on the pointer but its value is not changed until the nextstatement.


01 #include 0203 int main()04 {

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05 int ints[] = { 0, 1, 2, 3 };06 int* i1 = ints + 1;07 int* i2 = ints + 2;08 int a = ++*i1 + *i2++;09 int b = *++i1 + *i2--;10 printf("%d#%d", a, b);

11 return 0;12 }

5#6

4#6

4#5 - correct

Undefined behavior

Compiler error on line 9

description:The postfix increment operator has priority over the dereference operator whilethe prefix operator has the same precedence as the dereference operator. The dereferenceoperator and the prefix increment associate right to left.

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