Part -2 (15) C programming interview questions and answers

What is the difference between the 'switch' and 'if-else' statements in C? The 'switch' statement is used to execute different blocks of code based on the value of an expression, whereas the 'if-else' statement is used to execute different blocks of code based on the truth value of a condition. The 'switch' statement can be faster and more efficient than a series of 'if-else' statements when there are many possible values for the expression.

What is the purpose of the 'register' keyword in C? The 'register' keyword is used to specify that a variable should be stored in a register rather than in memory. This can improve the performance of a program by reducing the number of memory accesses and allowing for faster access to the variable.

How do you use the 'volatile' keyword in C? The 'volatile' keyword is used to indicate that a variable may be modified by an external source, such as an interrupt service routine. It tells the compiler to not optimize the access to the variable and always read from memory instead of from a register.

How do you use the 'restrict' keyword in C? The 'restrict' keyword is used to specify that the value of a pointer is the only way that a specific memory location can be accessed. It tells the compiler that the pointer is not aliased and the compiler can optimize the access accordingly.

What is the purpose of the 'inline' keyword in C? The 'inline' keyword is used to indicate that a function should be inlined, which is a form of optimization that replaces a function call with the body of the function. This can improve the performance of a program by reducing the overhead of function calls.

How can you use bitwise operations in C? Bitwise operations in C allow you to manipulate the individual bits of an integer or char type variables. Some of the common bitwise operations include bitwise AND(&), OR(|), XOR(^), NOT(~), left shift(<<), and right shift(>>). These operations can be useful for implementing low-level operations such as setting or clearing specific bits in a variable, or for creating efficient bit masks.

What is the purpose of the 'static' keyword when applied to functions in C? When applied to a function, the 'static' keyword limits the scope of the function to the current source file. It makes the function only visible and callable within the file it is defined, it is not accessible from other source files. This can be useful for functions that are only used within a specific module or for creating internal helper functions.

How can you use the 'extern' keyword in C? The 'extern' keyword is used to declare a variable or function that is defined in another source file. It tells the compiler that the variable or function is defined in another file and it should not allocate storage for it. It is used to create a reference to a global variable or function defined in another file.

How can you use macros in C? Macros in C are used to define a constant value or a short piece of code that can be reused throughout a program. They are defined using the '#define' preprocessor directive, followed by the name of the macro and its value. Macros can be useful for creating reusable constants, such as mathematical constants, or for creating short and simple functions that can be easily replaced with their corresponding code.

What is the purpose of the 'signed' and 'unsigned' keywords in C? The 'signed' and 'unsigned' keywords are used to specify the signedness of an integer type variable. A signed integer can represent negative and positive values, while an unsigned integer can only represent positive values. The signedness of an integer can affect the range of values that it can represent, and it can also affect the behavior of certain bitwise and arithmetic operations.

How can you use the 'typedef' keyword to create an alias for a function pointer in C? The 'typedef' keyword can be used to create an alias for a function pointer, which allows you to define a function pointer with a more meaningful and readable name. This can make your code more readable and reduce the likelihood of errors by making the code more self-explanatory. Syntax for this is: typedef return_type (*new_name)(parameter_list);

What is the difference between a 'preprocessor directive' and a 'compiler directive' in C? Preprocessor directives are instructions that are processed by the preprocessor before the code is compiled. They are used to include or exclude code, define constants and macros, and perform other tasks that affect the structure of the code. Compiler directives, on the other hand, are instructions that are processed by the compiler during the compilation process. They are used to specify options and settings that affect the behavior of the compiler, such as optimization level, warning level, and target architecture.

How can you use the 'assert' macro in C? The 'assert' macro in C is used to check for conditions at runtime. It is defined in the <assert.h> header file. The assert macro takes a single argument that is an expression that should evaluate to true. If the expression evaluates to false, the program will terminate and print an error message indicating that an assertion has failed, along with the source file name, the line number, and the failed expression.

How can you use the 'va_list', 'va_start', 'va_arg', and 'va_end' macros for variable arguments in C? The 'va_list', 'va_start', 'va_arg', and 'va_end' macros are used for variable arguments in C. The 'va_list' is a type that can hold information about a variable argument list. The 'va_start' macro is used to initialize a variable of type 'va_list' to the first argument in the variable argument list. The 'va_arg' macro is used to retrieve the next argument from the variable argument list, and the 'va_end' macro is used to clean up and free any resources used by the variable argument list.

How can you use the 'offsetof' macro in C? The 'offsetof' macro is defined in the <stddef.h> header file and it returns the offset of a member within a struct or union. It takes two arguments, the first is the type of the struct or union, and the second is the name of the member. It can be useful for accessing specific members of a struct or union at a specific offset, for example when working with binary data or low-level memory manipulation.