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1. What is C language?
Explanation: The C programming language is a standardized programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the UNIX operating system. It has since spread to many other operating systems, and is one of the most widely used programming languages. C is prized for its efficiency, and is the most popular programming language for writing system software, though it is also used for writing applications.

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2. printf() Function What is the output of printf("%d")?
Explanation: 1. When we write printf("%d",x); this means compiler will print the value of x. But as here, there is nothing after %d so compiler will show in output window garbage value. 2. When we use %d the compiler internally uses it to access the argument in the stack (argument stack). Ideally compiler determines the offset of the data variable depending on the format specification string. Now when we write printf("%d",a) then compiler first accesses the top most element in the argument stack of the printf which is %d and depending on the format string it calculated to offset to the actual data variable in the memory which is to be printed. Now when only %d will be present in the printf then compiler will calculate the correct offset (which will be the offset to access the integer variable) but as the actual data object is to be printed is not present at that memory location so it will print what ever will be the contents of that memory location. 3. Some compilers check the format string and will generate an error without the proper number and type of arguments for things like printf(...) and scanf(...).

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3. malloc() Function- What is the difference between "calloc(...)" and "malloc(...)"?
Explanation: 1. calloc(...) allocates a block of memory for an array of elements of a certain size. By default the block is initialized to 0. The total number of memory allocated will be (number_of_elements * size). malloc(...) takes in only a single argument which is the memory required in bytes. malloc(...) allocated bytes of memory and not blocks of memory like calloc(...). 2. malloc(...) allocates memory blocks and returns a void pointer to the allocated space, or NULL if there is insufficient memory available. calloc(...) allocates an array in memory with elements initialized to 0 and returns a pointer to the allocated space. calloc(...) calls malloc(...) in order to use the C _set_new_mode function to set the new handler mode.

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4. printf() Function- What is the difference between "printf(...)" and "sprintf(...)"?
Explanation: sprintf(...) writes data to the character array whereas printf(...) writes data to the standard output device.

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5. Compilation How to reduce a final size of executable?
Explanation: Size of the final executable can be reduced using dynamic linking for libraries.

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6. Linked Lists -- Can you tell me how to check whether a linked list is circular?
Explanation: Create two pointers, and set both to the start of the list. Update each as follows: while (pointer1) { pointer1 = pointer1->next; pointer2 = pointer2->next; if (pointer2) pointer2=pointer2->next; if (pointer1 == pointer2) { print ("circular"); }} If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, its either 1 or 2 jumps until they meet.

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7. "union" Data Type What is the output of the following program? Why?
Explanation: #include main() { typedef union { int a; char b[10]; float c; } Union; Union x,y = {100}; x.a = 50; strcpy(x.b,"hello"); x.c = 21.50; printf("Union x : %d %s %f n",x.a,x.b,x.c); printf("Union y : %d %s %f n",y.a,y.b,y.c); }

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8. What does static variable mean?
Explanation: there are 3 main uses for the static. 1. If you declare within a function: It retains the value between function calls 2.If it is declared for a function name: By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files 3. Static for global variables: By default we can use the global variables from outside files If it is static global..that variable is limited to with in the file

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9. Advantages of a macro over a function?
Explanation: Macro gets to see the Compilation environment, so it can expand __ __TIME__ __FILE__ #defines. It is expanded by the preprocessor. For example, you can%u2019t do this without macros #define PRINT(EXPR) printf( #EXPR %u201C=%d\n%u201D, EXPR) PRINT( 5 6*7 ) // expands into printf(%u201D5 6*7=%d%u201D, 5 6*7 ); You can define your mini language with macros: #define strequal(A,B) (!strcmp(A,B)) Macros are a necessary evils of life. The purists don%u2019t like them, but without it no real work gets done.

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10. What are the differences between malloc() and calloc()?
Explanation: There are 2 differences. First, is in the number of arguments. malloc() takes a single argument(memory required in bytes), while calloc() needs 2 arguments(number of variables to allocate memory, size in bytes of a single variable). Secondly, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.

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