Cognizant Frequently Asked C Language Interview Questions Answers
Explain The Purpose Of Main( ) Function?
The function main( ) invokes other functions within it.It is the first function to be called when the program starts execution.
It is the starting function.
It returns an int value to the environment that called the program.
Recursive call is allowed for main( ) also.
It is a user-defined function.
Program execution ends when the closing brace of the function main( ) is reached.
It has two arguments argument count and.
argument vector (represents strings passed).
Any user-defined name can also be used as parameters for main( ) instead of argc and argv.
Write The Equivalent Expression For X%8?
x&7.
Why N++ Executes Faster Than N+1?
The expression n++ requires a single machine instruction such as INR to carry out the increment operation whereas n+1 requires more instructions to carry out this operation.
Can The Sizeof Operator Be Used To Tell The Size Of An Array Passed To A Function?
No. There’s no way to tell, at runtime, how many elements are in an array parameter just by looking at the array parameter itself. Remember, passing an array to a function is exactly the same as passing a pointer to the first element.
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 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.
Write About 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.
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.
Why Is That We Have To Assign Null To The Elements (pointer) After Freeing Them?
This is paranoia based on long experience. After a pointer has been freed, you can no longer use the pointed-to data. The pointer is said to “dangle”; it doesn’t point at anything useful. If you “NULL out” or “zero out” a pointer immediately after freeing it, your program can no longer get in trouble by using that pointer. True, you might go indirect on the null pointer instead, but that’s something your debugger might be able to help you with immediately. Also, there still might be copies of the pointer that refer to the memory that has been deallocated; that’s the nature of C. Zeroing out pointers after freeing them won’t solve all problems.
Differentiate Between A String Copy (strcpy) And A Memory Copy (memcpy)? When Should Each Be Used?
The strcpy() function is designed to work exclusively with strings. It copies each byte of the source string to the destination string and stops when the terminating null character () has been moved. On the other hand, the memcpy () function is designed to work with any type of data. Because not all data ends with a null character, you must provide the memcpy () function with the number of bytes you want to copy from the source to the destination.
How Can You Check To See Whether A Symbol Is Defined?
You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
How Do You Override A Defined Macro?
You can use the #undef preprocessor directive to undefine (override) a previously defined macro.
What Is #line Used For?
The #line preprocessor directive is used to reset the values of the _ _LINE_ _ and _ _FILE_ _ symbols, respectively. This directive is commonly used in fourth-generation languages that generate C language source files.
What Is A Pragma?
The #pragma preprocessor directive allows each compiler to implement compiler-specific features that can be turned on and off with the #pragma statement. For instance, your compiler might support a feature called loop optimization. This feature can be invoked as a command-line option or as a #pragma directive. To implement this option using the #pragma directive, you would put the following line into your code
#pragma loop_opt(on).
What Are The Standard Predefined Macros?
The ANSI C standard defines six predefined macros for use in the C language
Macro Name Purpose
_ _LINE_ _ Inserts the current source code line number in your code.
_ _FILE_ _ Inserts the current source code filename in your code.
_ _DATE_ _ Inserts the current date of compilation in your code.
_ _TIME_ _ Inserts the current time of compilation in your code.
_ _cplusplus Is defined if you are compiling a C++ program.
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.
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.
Define Which Header File To Include At Compile Time?
Yes. This can be done by using the #if, #else, and #endif preprocessor directives. For example, certain compilers use different names for header files. One such case is between Borland C++, which uses the header file alloc.h, and Microsoft C++, which uses the header file malloc.h. Both of these headers serve the same purpose, and each contains roughly the same definitions. If, however, you are writing a program that is to support Borland C++ and Microsoft C++, you must define which header to include at compile time. The following example shows how this can be done
#ifdef _ _BORLANDC_ _
#include #else #include #endif.
When Would You Use A Pointer To A Function?
Pointers to functions are interesting when you pass them to other functions. A function that takes function pointers says, in effect, “Part of what I do can be customized. Give me a pointer to a function, and I’ll call it when that part of the job needs to be done. That function can do its part for me.” This is known as a “callback.” It’s used a lot in graphical user interface libraries, in which the style of a display is built into the library but the contents of the display are part of the application.
As a simpler example, say you have an array of character pointers (char*s), and you want to sort it by the value of the strings the character pointers point to. The standard qsort() function uses function pointers to perform that task. qsort() takes four arguments,
a pointer to the beginning of the array,
the number of elements in the array,
the size of each array element, and,
a comparison function, and returns an int.
What Does It Mean When A Pointer Is Used In An If Statement?
Any time a pointer is used as a condition, it means “Is this a non-null pointer?” A pointer can be used in an if, while, for, or do/while statement, or in a conditional expression.
Is Null Always Defined As 0?
NULL is defined as either 0 or (void*)0. These values are almost identical; either a literal zero or a void pointer is converted automatically to any kind of pointer, as necessary, whenever a pointer is needed (although the compiler can’t always tell when a pointer is needed).
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
To stop indirection in a recursive data structure
As an error value
As a sentinel value
Mention The Levels Of Pointers Can You Have?
The
depends on what you mean by “levels of pointers.” If you mean “How many levels of indirection can you have in a single declaration?” the
is “At least 12.”
int i = 0;
int *ip01 = & i;
int **ip02 = & ip01;
int ***ip03 = & ip02;
int ****ip04 = & ip03;
int *****ip05 = & ip04;
int ******ip06 = & ip05;
int *******ip07 = & ip06;
int ********ip08 = & ip07;
int *********ip09 = & ip08;
int **********ip10 = & ip09;
int ***********ip11 = & ip10;
int ************ip12 = & ip11;
************ip12 = 1; /* i = 1 */
The ANSI C standard says all compilers must handle at least 12 levels. Your compiler might support more.
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.
How Do You Print Only Part Of A String?
/* Use printf () to print the first 11 characters of source_str. */
printf (“First 11 characters: ‘%11.11s’n”, source_str);
How To Convert A String To A Number?
The standard C library provides several functions for converting strings to numbers of all formats (integers, longs, floats, and so on) and vice versa.
The following functions can be used to convert strings to numbers
Function Name Purpose
atof(): Converts a string to a double-precision floating-point value.
atoi(): Converts a string to an integer.
atol(): Converts a string to a long integer.
How To Convert A Number To A String?
The standard C library provides several functions for converting numbers of all formats (integers, longs, floats, and so on) to strings and vice versa The following functions can be used to convert integers to strings
Function Name Purpose
iota(): Converts an integer value to a string.
ltoa (): Converts a long integer value to a string.
ultoa (): Converts an unsigned long integer value to a string.
The following functions can be used to convert floating-point values to strings
Function Name Purpose
ecvt() : Converts a double-precision floating-point value to a string without an embedded decimal point.
fcvt(): Same as ecvt(), but forces the precision to a specified number of digits.
gcvt(): Converts a double-precision floating-point value to a string with an embedded decimal point.
strtod(): Converts a string to a double-precision floating-point value and reports any “leftover” numbers that could not be converted.
strtol(): Converts a string to a long integer and reports any “leftover” numbers that could not be converted.
strtoul(): Converts a string to an unsigned long integer and reports any “leftover” numbers that could not be converted.
Explain The Purpose Of Main( ) Function?
The function main( ) invokes other functions within it.It is the first function to be called when the program starts execution.
It is the starting function.
It returns an int value to the environment that called the program.
Recursive call is allowed for main( ) also.
It is a user-defined function.
Program execution ends when the closing brace of the function main( ) is reached.
It has two arguments argument count and.
argument vector (represents strings passed).
Any user-defined name can also be used as parameters for main( ) instead of argc and argv.
Write The Equivalent Expression For X%8?
x&7.
Why N++ Executes Faster Than N+1?
The expression n++ requires a single machine instruction such as INR to carry out the increment operation whereas n+1 requires more instructions to carry out this operation.
Can The Sizeof Operator Be Used To Tell The Size Of An Array Passed To A Function?
No. There’s no way to tell, at runtime, how many elements are in an array parameter just by looking at the array parameter itself. Remember, passing an array to a function is exactly the same as passing a pointer to the first element.
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 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.
Write About 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.
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.
 |
| Cognizant Frequently Asked C Language Interview Questions Answers |
This is paranoia based on long experience. After a pointer has been freed, you can no longer use the pointed-to data. The pointer is said to “dangle”; it doesn’t point at anything useful. If you “NULL out” or “zero out” a pointer immediately after freeing it, your program can no longer get in trouble by using that pointer. True, you might go indirect on the null pointer instead, but that’s something your debugger might be able to help you with immediately. Also, there still might be copies of the pointer that refer to the memory that has been deallocated; that’s the nature of C. Zeroing out pointers after freeing them won’t solve all problems.
Differentiate Between A String Copy (strcpy) And A Memory Copy (memcpy)? When Should Each Be Used?
The strcpy() function is designed to work exclusively with strings. It copies each byte of the source string to the destination string and stops when the terminating null character () has been moved. On the other hand, the memcpy () function is designed to work with any type of data. Because not all data ends with a null character, you must provide the memcpy () function with the number of bytes you want to copy from the source to the destination.
How Can You Check To See Whether A Symbol Is Defined?
You can use the #ifdef and #ifndef preprocessor directives to check whether a symbol has been defined (#ifdef) or whether it has not been defined (#ifndef).
How Do You Override A Defined Macro?
You can use the #undef preprocessor directive to undefine (override) a previously defined macro.
What Is #line Used For?
The #line preprocessor directive is used to reset the values of the _ _LINE_ _ and _ _FILE_ _ symbols, respectively. This directive is commonly used in fourth-generation languages that generate C language source files.
What Is A Pragma?
The #pragma preprocessor directive allows each compiler to implement compiler-specific features that can be turned on and off with the #pragma statement. For instance, your compiler might support a feature called loop optimization. This feature can be invoked as a command-line option or as a #pragma directive. To implement this option using the #pragma directive, you would put the following line into your code
#pragma loop_opt(on).
What Are The Standard Predefined Macros?
The ANSI C standard defines six predefined macros for use in the C language
Macro Name Purpose
_ _LINE_ _ Inserts the current source code line number in your code.
_ _FILE_ _ Inserts the current source code filename in your code.
_ _DATE_ _ Inserts the current date of compilation in your code.
_ _TIME_ _ Inserts the current time of compilation in your code.
_ _cplusplus Is defined if you are compiling a C++ program.
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.
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.
Define Which Header File To Include At Compile Time?
Yes. This can be done by using the #if, #else, and #endif preprocessor directives. For example, certain compilers use different names for header files. One such case is between Borland C++, which uses the header file alloc.h, and Microsoft C++, which uses the header file malloc.h. Both of these headers serve the same purpose, and each contains roughly the same definitions. If, however, you are writing a program that is to support Borland C++ and Microsoft C++, you must define which header to include at compile time. The following example shows how this can be done
#ifdef _ _BORLANDC_ _
#include #else #include #endif.
When Would You Use A Pointer To A Function?
Pointers to functions are interesting when you pass them to other functions. A function that takes function pointers says, in effect, “Part of what I do can be customized. Give me a pointer to a function, and I’ll call it when that part of the job needs to be done. That function can do its part for me.” This is known as a “callback.” It’s used a lot in graphical user interface libraries, in which the style of a display is built into the library but the contents of the display are part of the application.
As a simpler example, say you have an array of character pointers (char*s), and you want to sort it by the value of the strings the character pointers point to. The standard qsort() function uses function pointers to perform that task. qsort() takes four arguments,
a pointer to the beginning of the array,
the number of elements in the array,
the size of each array element, and,
a comparison function, and returns an int.
What Does It Mean When A Pointer Is Used In An If Statement?
Any time a pointer is used as a condition, it means “Is this a non-null pointer?” A pointer can be used in an if, while, for, or do/while statement, or in a conditional expression.
Is Null Always Defined As 0?
NULL is defined as either 0 or (void*)0. These values are almost identical; either a literal zero or a void pointer is converted automatically to any kind of pointer, as necessary, whenever a pointer is needed (although the compiler can’t always tell when a pointer is needed).
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
To stop indirection in a recursive data structure
As an error value
As a sentinel value
Mention The Levels Of Pointers Can You Have?
The
depends on what you mean by “levels of pointers.” If you mean “How many levels of indirection can you have in a single declaration?” the
is “At least 12.”
int i = 0;
int *ip01 = & i;
int **ip02 = & ip01;
int ***ip03 = & ip02;
int ****ip04 = & ip03;
int *****ip05 = & ip04;
int ******ip06 = & ip05;
int *******ip07 = & ip06;
int ********ip08 = & ip07;
int *********ip09 = & ip08;
int **********ip10 = & ip09;
int ***********ip11 = & ip10;
int ************ip12 = & ip11;
************ip12 = 1; /* i = 1 */
The ANSI C standard says all compilers must handle at least 12 levels. Your compiler might support more.
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.
How Do You Print Only Part Of A String?
/* Use printf () to print the first 11 characters of source_str. */
printf (“First 11 characters: ‘%11.11s’n”, source_str);
How To Convert A String To A Number?
The standard C library provides several functions for converting strings to numbers of all formats (integers, longs, floats, and so on) and vice versa.
The following functions can be used to convert strings to numbers
Function Name Purpose
atof(): Converts a string to a double-precision floating-point value.
atoi(): Converts a string to an integer.
atol(): Converts a string to a long integer.
How To Convert A Number To A String?
The standard C library provides several functions for converting numbers of all formats (integers, longs, floats, and so on) to strings and vice versa The following functions can be used to convert integers to strings
Function Name Purpose
iota(): Converts an integer value to a string.
ltoa (): Converts a long integer value to a string.
ultoa (): Converts an unsigned long integer value to a string.
The following functions can be used to convert floating-point values to strings
Function Name Purpose
ecvt() : Converts a double-precision floating-point value to a string without an embedded decimal point.
fcvt(): Same as ecvt(), but forces the precision to a specified number of digits.
gcvt(): Converts a double-precision floating-point value to a string with an embedded decimal point.
strtod(): Converts a string to a double-precision floating-point value and reports any “leftover” numbers that could not be converted.
strtol(): Converts a string to a long integer and reports any “leftover” numbers that could not be converted.
strtoul(): Converts a string to an unsigned long integer and reports any “leftover” numbers that could not be converted.
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