What is C language?
Language is a collection of words and symbols which can be used to perform certain task or activities and to establish a communication between person to person.
In the same manner computer languages are the collection of predefine key words which can be used to perform certain task and to communicate between to entities like between two machines or between human and computers or computers and others peripherals.
There are three different level of programming languages. They are
(1) Machine languages (low level)
(2) Assembly languages
(3) Procedure Oriented languages (high level)
(4) Fourth Generation languages (4 GLS)
What is Operator ?
Operator is symbol, which represents, a particular operation that can be performed on some data. The data itself (which can be either a variable or a constant) is called the “operand”. The operator thus operates on operand. They are Classified as
(1)Arithmetic
(2)relational
(3)logical
(4)Assignment
(5)increment/decrement
(6)conditional
(7)bitwise
(8)special
Difference of Compiler – Interpreter :-
Error finding is much easier in Interpreter because it checks and executes each statement at a time. So wherever it fine some error it will stop the execution. Where Compiler first check all the statement for error and provide lists of all the errors in the program.
Interpreter take more time for the execution of a program compared to Compilers because it translates and executes each statement one by one.
Printf() function :
Printf() function is use to display something on the console or to display the value of some variable on the console The general syntax for printf() function is as follows
printf(<”format string”>,<list of variables>);
To print some message on the screen
Printf(“God is great”);
This will print message “God is great” on the screen or console.
Scanf() function is use to read data from keyboard and to store that data in the variables. The general syntax for scanf() function is as follows.
Scanf(“Format string1,format string2”,&variable1,&variable2);
For Integer Variable :
Int rollno;
Scanf(“%d”,&rollno);
Printf(“Enter rollno=”);
Here in scanf() function %d is a format string for integer variable and &rollno will give the address of variable rollno to store the value at variable rollno location.
Single character input – the getchar function :
Single characters can be entered into the computer using the “C” library function getchar. The getchar function is a part of the standard “C” language I/O library. It returns a single character from a standard input device (typically a keyboard). The function does not required any arguments through a pair of empty parentheses must follow the word getchar.
In general terms, a reference to the getchar function is written as.
Character variable=getchar();
Single character output – The putchar function:
Single character can be displayed (i.e. written out of the computer) using the C library function putchar.The putchar function, like getchar is a part of the standard “C” language I/O library.
It transmits a single character to a standard output device. The character being transmitted will normally be represented as a character-type variable. It must be expressed as an argument to the function, enclosed in parentheses following the word putchar.
In general a reference to the putchar function is written as
Putchar (character variable)
Where character variable refers to some previously declared character variable.
A “C” program contains the following statements.:
char c=’a’;
putchar(c);
What is Loop Control Structure ?
If we want to perform certain action for no of times or we want to execute same statement or a group of statement repeatedly then we can use different type of loop structure available in C.
Basically there are 3 types of loop structure available in C
(1) While loop
(2) Do..while
(3) For loop
(1) While loop
The while statement is used to carry out looping operations. The general form of the statements
Initialization;
While(exp)
{
statement 1;
statement 2;
increment/ decrement;
}
(2) Do..while
Sometimes, however, it is desirable to have a loop with the test for continuation at the end or each pass. This can be accomplished by means of the do-while statement.
The general form of do-while statement is
Do
{
statement1;
statement2;
increment/decrement operator;
} while(expression);
(3) For loop
The for statement is another entry controller that provides a more concise loop control structure. The general form of the for loop is :
For(initialization, test condition, increment)
{
statement 1;
statement 2;
}
| Array is a collection or group of similar data type elements stored in contiguous memory. The |
What is Break Statement ?
The break statement is used to terminate loops or to exit a switch. The break statement will break or terminate the inner-most loop. It can be used within a while, a do-while, a for or a switch statement. The break statement is written simply as break; Without any embedded expressions or statement.
For example,
For(I=1; I<=10; I++)
{
if(I==5)
break;
printf(“\nI=%d”,I);
}
The output will be 1,2,3,4 and then break will terminate this loop and stop the execution of the for loop.
The continue statement is used to skip or to bypass some step or iteration of looping structure. It does not terminate the loop but just skip or bypass the particular sequence of the loop structure. It is simply written as continue;.
For(I=1; I<=10; I++)
{
if(I==5)
continue;
printf(“\nI=%d”,I);
}
The output of the above program will be 1,2,3,4,6,7,8,9,10. The 5th iteration of the loop will be skipped as we have define the continue for that iteration. So it will not print the value ‘5’.
The switch statement causes a particular group of statements to be chosen from several available groups. The selection is based upon the current value of an expression that is included within a switch statement. The general form of switch-case statement is :
Switch(expression)
{
Case expression1
Statement1;
Statement2;
Case expression2
Statement1;
Statement2;
Case expression3
Statement1;
Statement2;
}
The goto statement is used to alter the normal sequence of program execution by transferring control to some other part of the program. In its general for the goto statement is written as goto label; Where label is an identifier used to label the target statement to which control will be transferred.
What is Array ?
Array is a collection or group of similar data type elements stored in contiguous memory. The individual data items can be characters, integers, floating points numbers and so on .
What is Multidimensional Array ?
Multidimensional, array is defined in much the same manner as one-dimensional arrays, except that a separate pair of square brackets is required for each subscript.
Thus a two dimensional array will require two pairs of square brackets, three dimensional array will require three pairs of square brackets and so on.
In general terms, a multidimensional array definition can be written as
Storage_class data_type array[exp1][exp2]…[expn];
For Example:
Float table [50][50];
Char page[24][80];
Static double records[100][66][255];
Static double records[L][M][N];
| DEFINING A FUNCTION : A function has three principal components : the first line, the argument declarations the body of the function The first line of a function definition contains the byte specification of the value returned byte the function, followed by the function name and (optionally) a set of parameters separated by comas and enclosed in parenthesis. The type specification can be omitted if the function returns an integer or a character, in entry pair of parenthesis must follow the function name if the function definition does not include any arguments. In general terms, the first line can be |
DEFINING A FUNCTION :
A function has three principal components :
the first line,
the argument declarations
the body of the function
The first line of a function definition contains the byte specification of the value returned byte the function, followed by the function name and (optionally) a set of parameters separated by comas and enclosed in parenthesis.
The type specification can be omitted if the function returns an integer or a character, in entry pair of parenthesis must follow the function name if the function definition does not include any arguments. In general terms, the first line can be written as :
Data-type name(formal arg1, arg2, argn)
Where data type represents the data type of the value, which is returned, and name represents
the function name.
For Example:
Low-to-up(Char el)
{
char c2
c2 = c1>=’a’ && c1<=’z’) ? (‘A’+cl-‘a’) : cl;
return c2;
}
Difference between const char* p and char const* p
In const char* p, the character pointed by ‘p’ is constant, so u cant change the value of character pointed by p but u can make ‘p’ refer to some other location.
in char const* p, the ptr ‘p’ is constant not the character referenced by it, so u cant make ‘p’ to reference to any other location but u can change the value of the char pointed by ‘p’.
How can you determine the size of an allocated portion of memory?
You can’t, really. free() can , but there’s no way for your program to know the trick free() uses. Even if you disassemble the library and discover the trick, there’s no guarantee the trick won’t change with the next release of the compiler.
Can static variables be declared in a header file?
You can’t declare a static variable without defining it as well (this is because the storage class modifiers static and extern are mutually exclusive).
A static variable can be defined in a header file, but this would cause each source file that included the header file to have its own private copy of the variable, which is probably not what was intended.
Can a variable be both const and volatile?
Yes. The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code. For instance, in the example in FAQ 8, the timer structure was accessed through a volatile const pointer.
The function itself did not change the value of the timer, so it was declared const. However, the value was changed by hardware on the computer, so it was declared volatile. If a variable is both const and volatile, the two modifiers can appear in either order.
Can include files be nested?
Yes. Include files can be nested any number of times. As long as you use precautionary measures , you can avoid including the same file twice. In the past, nesting header files was seen as bad programming practice, because it complicates the dependency tracking function of the MAKE program and thus slows down compilation. Many of today’s popular compilers make up for this difficulty by implementing a concept called precompiled headers, in which all headers and associated dependencies are stored in a precompiled state.
Many programmers like to create a custom header file that has
#include statements for every header needed for each module. This is perfectly acceptable and can help avoid potential problems relating to
#include files, such as accidentally omitting an #include file in a
module.
When does the compiler not implicitly generate the address of the first element of an array?
Whenever an array name appears in an expression such as
- array as an operand of the sizeof operator
- array as an operand of & operator
- array as a string literal initializer for a character array
Then the compiler does not implicitly generate the address of the
address of the first element of an array.
What is a null pointer?
There are times when it’s necessary to have a pointer that doesn’t point to anything. The macro NULL, defined in , has a value that’s guaranteed to be different from any valid pointer.
NULL is a literal zero, possibly cast to void* or char*. Some people, notably C++ programmers, prefer to use 0 rather than NULL.
The null pointer is used in three ways:
1) To stop indirection in a recursive data structure
2) As an error value
3) As a sentinel value
What is the difference between text and binary modes?
Streams can be classified into two types: text streams and binary streams. Text streams are interpreted, with a maximum length of 255 characters.
With text streams, carriage return/line feed combinations are translated to the newline n character and vice versa. Binary streams are uninterrupted and are treated one byte at a time with no translation of characters.
Typically, a text stream would be used for reading and writing standard text files, printing output to the screen or printer, or receiving input from the keyboard.
A binary text stream would typically be used for reading and writing binary files such as graphics or word processing documents, reading mouse input, or reading and writing to the modem.
What is static memory allocation and dynamic memory allocation?
Static memory allocation: The compiler allocates the required memory space for a declared variable.
By using the address of operator,the reserved address is obtained and this address may be assigned to a pointer variable.Since most of the declared variable have static memory,this way of assigning pointer value to a pointer variable is known as static memory allocation. memory is assigned during compilation time.
Dynamic memory allocation: It uses functions such as malloc( ) or calloc( ) to get memory dynamically.If these functions are used to get memory dynamically and the values returned by these functions are assingned to pointer variables, such assignments are known as dynamic memory allocation.memory is assined during run time.
When should a far pointer be used?
Sometimes you can get away with using a small memory model in most of a given program. There might be just a few things that don’t fit in your small data and code segments. When that happens, you can use explicit far pointers and function declarations to get at the rest of memory.
A far function can be outside the 64KB segment most functions are shoehorned into for a small-code model. (Often, libraries are declared explicitly far, so they’ll work no matter what code model the program uses.) A far pointer can refer to information outside the
64KB data segment. Typically, such pointers are used with farmalloc() and such, to manage a heap separate from where all the rest of the data lives. If you use a small-data, large-code model, you should explicitly make your function pointers far.
How are pointer variables initialized?
Pointer variable are initialized by one of the following two ways
- Static memory allocation
- Dynamic memory allocation
Difference between arrays and pointers?
- Pointers are used to manipulate data using the address. Pointers use * operator to access the data pointed to by them
- Arrays use subscripted variables to access and manipulate data. Array variables can be equivalently written using pointer expression.
Is using exit() the same as using return?
No. The exit() function is used to exit your program and return control to the operating system. The return statement is used to return from a function and return control to the calling function.
If you issue a return from the main() function, you are essentially returning control to the
calling function, which is the operating system. In this case, the return statement and exit() function are similar.
What is a method?
Method is a way of doing something, especially a systematic way; implies an orderly logical arrangement (usually in steps).
What is indirection?
If you declare a variable, its name is a direct reference to its value. If you have a pointer to a variable, or any other object in memory, you have an indirect reference to its value.
What is modular programming?
If a program is large, it is subdivided into a number of smaller programs that are called modules or subprograms. If a complex problem is solved using more modules, this approach is known as modular programming.
How many levels deep can include files be nested?
Even though there is no limit to the number of levels of nested include files you can have, your compiler might run out of stack space while trying to include an inordinately high number of files. This number varies according to your hardware configuration and possibly your compiler.
What is the difference between declaring a variable and defining a variable?
Declaring a variable means describing its type to the compiler but not allocating any space for it. Defining a variable means declaring it and also allocating space to hold the variable. You can also initialize a variable at the time it is defined.
What is an lvalue?
An lvalue is an expression to which a value can be assigned. The lvalue expression is located on the left side of an assignment statement, whereas an rvalue is located on the right side of an assignment statement. Each assignment statement must have an lvalue and an rvalue. The lvalue expression must reference a storable variable in memory. It cannot be a constant.
Differentiate between an internal static and external static variable?
An internal static variable is declared inside a block with static storage class whereas an external static variable is declared outside all the blocks in a file.An internal static variable has persistent storage,block scope and no linkage.An external static variable has permanent storage,file scope and internal linkage.
What is the difference between a string and an array?
An array is an array of anything. A string is a specific kind of an array with a well-known convention to determine its length.There are two kinds of programming languages: those in which a string is just an array of characters, and those in which it’s a special type.
In C, a string is just an array of characters (type char), with one wrinkle: a C string always ends with a NUL character.The “value” of an array is the same as the address of (or a pointer to) the first element; so, frequently, a C string and a pointer to char are
used to mean the same thing.
An array can be any length. If it’s passed to a function, there’s no way the function can tell how long the array is supposed to be, unless some convention is used. The convention for strings is NUL termination; the last character is an ASCII NUL (‘’) character.
What is an argument? Differentiate between formal arguments and actual arguments?
An argument is an entity used to pass the data from calling function to the called function. Formal arguments are the arguments available in the function definition. They are preceded by their own data types. Actual arguments are available in the function call.
What are advantages and disadvantages of external storage class?
Advantages of external storage class
1)Persistent storage of a variable retains the latest value
2)The value is globally available
Disadvantages of external storage class
1)The storage for an external variable exists even when the variable is
not needed
2)The side effect may produce surprising output
3)Modification of the program is difficult
4)Generality of a program is affected
What is a void pointer?
A void pointer is a C convention for a raw address. The compiler has no idea what type of object a void Pointer really points to. If you write
int *ip;
ip points to an int. If you write
void *p;
p doesn’t point to a void!
In C and C++, any time you need a void pointer, you can use another pointer type. For example, if you have a char*, you can pass it to a function that expects a void*. You don’t even need to cast it. In C (but not in C++), you can use a void* any time you need any kind of pointer, without casting. (In C++, you need to cast it).
A void pointer is used for working with raw memory or for passing a pointer to an unspecified type.
Some C code operates on raw memory. When C was first invented, character pointers (char *) were used for that. Then people started getting confused about when a character pointer was a string, when it was a character array, and when it was raw memory.
When should a type cast not be used?
A type cast should not be used to override a const or volatile declaration. Overriding these type modifiers can cause the program to fail to run correctly.
A type cast should not be used to turn a pointer to one type of structure or data type into another. In the rare events in which this action is beneficial, using a union to hold the values makes the programmer’s intentions clearer.
When is a switch statement better than multiple if statements?
A switch statement is generally best to use when you have more than two conditional expressions based on a single variable of numeric type.
What is a static function?
A static function is a function whose scope is limited to the current source file. Scope refers to the visibility of a function or variable. If the function or variable is visible outside of the current source file, it is said to have global, or external, scope. If the function or variable is not visible outside of the current source file, it is said to have local, or static, scope.
What is a pointer variable?
A pointer variable is a variable that may contain the address of another variable or any valid address in the memory.
What is a pointer value and address?
A pointer value is a data object that refers to a memory location. Each memory location is numbered in the memory. The number attached to a memory location is called the address of the location.
What is a modulus operator? What are the restrictions of a modulus operator?
A Modulus operator gives the remainder value. The result of x%y is obtained by (x-(x/y)*y). This operator is applied only to integral operands and cannot be applied to float or double.
Differentiate between a linker and linkage?
A linker converts an object code into an executable code by linking together the necessary build in functions. The form and place of declaration where the variable is declared in a program determine the linkage of variable.
What is a function and built-in function?
A large program is subdivided into a number of smaller programs or subprograms. Each subprogram specifies one or more actions to be performed for a large program. such subprograms are functions.
The function supports only static and extern storage classes. By default, function assumes extern storage class. functions have global scope. Only register or auto storage class is allowed in the function parameters.
Built-in functions that predefined and supplied along with the compiler are known as built-in functions. They are also known as library functions.
Why should I prototype a function?
A function prototype tells the compiler what kind of arguments a function is looking to receive and what kind of return value a function is going to give back.
This approach helps the compiler ensure that calls to a function are made correctly and that no erroneous type conversions are taking place.
What is Polymorphism ?
'Polymorphism' is an object oriented term. Polymorphism may be defined as the ability of related objects to respond to the same message with different, but appropriate actions. In other words, polymorphism means taking more than one form.
Polymorphism leads to two important aspects in Object Oriented terminology - Function
Overloading and Function Overriding. Overloading is the practice of supplying more than one definition for a given function name in the same scope.
The compiler is left to pick the appropriate version of the function or operator based on the arguments with which it is called. Overriding refers to the modifications made in the sub class to the inherited methods from the base class to change their behavior.
What is Operator overloading ?
When an operator is overloaded, it takes on an additional meaning relative to a certain class. But it can still retain all of its old meanings.
Examples:
1) The operators >> and << may be used for I/O operations because in the header, they are overloaded.
2) In a stack class it is possible to overload the + operator so that it appends the contents of one stack to the contents of another. But the + operator still retains its original meaning relative to other types of data.
What is the difference between goto and longjmp() and setjmp()?
A goto statement implements a local jump of program execution, and the longjmp() and setjmp() functions implement a nonlocal, or far, jump of program execution.
Generally, a jump in execution of any kind should be avoided because it is not considered good programming practice to use such statements as goto and longjmp in your program.
A goto statement simply bypasses code in your program and jumps to a predefined position. To use the goto statement, you give it a labeled position to jump to. This predefined position must be within the same function.
You cannot implement gotos between functions. When your program calls setjmp(), the current state of your program is saved in a structure of type jmp_buf. Later, your program can call the longjmp() function to restore the program’s state as it was when you called setjmp().Unlike the goto statement, the longjmp() and setjmp() functions do not need to be implemented in the same function.
However, there is a major drawback to using these functions: your program, when restored to its previously saved state, will lose its references to any dynamically allocated memory between the longjmp() and the setjmp().
This means you will waste memory for every malloc() or calloc() you have implemented between your longjmp() and setjmp(), and your program will be horribly inefficient.
It is highly recommended that you avoid using functions such as longjmp() and setjmp() because they, like the goto statement, are quite often an indication of poor programming practice.
Article of : "C Interview Questions And Answers For Fresher"
Give Your Feedback ...