C Language Questions and Answers | C programming Important Questions with answers

Q1. What is a string constant?

Ans: A string constant is a group of characters surrounded by double quotes. These characters may be letters, numbers or any special characters.

 Example:   "Hello! World", "2015", "welcome"

Q2. Briefly explain the stages in array initialization.

Ans: An array can be declared and initialized in various ways.

Array Declaration by Initializing Elements

An array can be initialized at the time of its declaration. In this method of array declaration, the compiler will allocate an array of size equal to the number of the array elements. The following syntax can be used to declare and initialize an array at the same time.

int array[] = {10, 20, 30 40, 50};

In the above syntax, an array of 5 elements is created and even though the array size has not been specified here, the compiler will allocate a size of 5 integer elements.

Array Declaration by Specifying the Size and Initializing Elements

An array can also be created by specifying the size and assigning array elements at the time of declaration. This method of array creation is different from the previous one. Here, if the number of initialized elements is less than the size of the array specified, then the rest of the elements will automatically be initialized to 0 by the compiler. The number of initialized elements cannot be larger than the size of the array.

int array1[5] = {100, 200, 300, 400, 500};

int array2[5] = {100, 200, 300}; 

In the above array syntax, my_array1 is an array of size 5 with all five elements initialized. Whereas, my_array2 is an array of size 5 with only three of its elements initialized. The remaining two elements of the second array will be initialized to 0 by the compiler.

array2 = {100, 200, 300, 0, 0};

Array Initialization Using a Loop

An array can also be initialized using a loop. The loop iterates from 0 to (size - 1) for accessing all indices of the array starting from 0. The following syntax uses a “for loop” to initialize the array elements. This is the most common way to initialize an array in C.

// declare an array.

int array[5];

// initialize array using a "for" loop.

int i;

for(i = 0; i < 5; i++) 

{

    array[i] = 2 * i;

}

// array = {0, 2, 4, 6, 8}  

In the above syntax, an array of size 5 is declared first. The array is then initialized using a for loop that iterates over the array starting from index 0 to 4.

 

Q3. Explain the concept of recursive function with example.

Ans: In C, it is possible for the function to call itself. The function which calls itself is known as recursive function.

A recursive function is a function defined in terms of itself via self-calling expressions. This means that the function will continue to call itself and repeat its behavior until some condition is satisfied to return a value.

Recursive functions allow programmers to write efficient programs using a minimal amount of code. 

The recursive functions should be used very carefully because, when a function called by itself it enters into the infinite loop. And when a function enters into the infinite loop, the function execution never gets completed. We should define the condition to exit from the function call so that the recursive function gets terminated.

Recursive functions are very useful to solve many mathematical problems, such as calculating the factorial of a number, generating Fibonacci series, etc.

Recursive function example:

Program to find factorial of a given number recursively to illustrate recursive function

#include<stdio.h>

#include<conio.h>

long int fact(int n);

int main( )

{

 int num,f;

 printf(“\n Enter a number: ”);

 scanf(“%d”,&num);

 f=fact(num);

 printf(“\nFactorial of %d is :%ld”,num,f);

 getch();

 return 0;

}

long int fact(int n)

    {

     if (n<=1)

         return (1);

     else

         return (n*fact(n-1)) ;

    }

 

Output: 

Enter a number: 4

Factorial of 4 is: 24

The function fact calls itself repeatedly with n-1 and terminate when the variable becomes 1.

Q4. What is string? Write any two string function with their action.

Ans: A string is any sequence of characters. In C strings and arrays of characters are exactly the same thing. It is always terminated by the NULL character. Common string operations include finding lengths, copying, searching, replacing and counting the occurrences of specific characters and words.

Following are two useful string handling functions supported by C.

·        strlen()

·        strcpy()

These functions are defined in string.h header file. Hence we need to include this header file whenever we use these string handling functions in the program.

strlen()

This is the string length function. It is used to find out the length of a string i.e. the number of characters in the string excluding the terminating NULL character. It accepts a single argument which is pointer to the first character of the string.

Syntax:

strlen( string )

For example:

printf ( "%d", strlen( "Sumit" )) ;

would print out 5. (Note that the terminator is not counted as a character in the string.)

strcpy():

This is the string copy function.  It is used to copy one string into another string.

The function strcpy(str1,str2) copies str2 to str1 including the NULL character. Here str2 is the source string and str1 is the destination string. The old content of the destination string str1 are lost. The function returns a pointer to destination string str1.

Syntax:

strcpy(destination_String,source_String);

char ch1[20] = "Hello World" ;

char ch2[20];

 strcpy( ch2, ch1) ;

 would result in ch2 holding the string "Hello World".

Q5. Draw the basic structure of a C programming.

Ans: Every C program is basically a group of different section that is used for different purpose. The structure gives us a basic idea of the order of the sections in a program. A well-defined structured layout makes program more readable, easy to modify, consistent format and gives better clarity and the concept of a program. Whenever we write a program in ‘C’ language, we can divide that program into six different sections. These sections are as follows:

• Documentation section
• Linkage section
• User definition section
• Global declaration section
• Main() function section
• Subprogram section

Pictorial Representation of Basic Structure of C Programming:

            

             

Figure: Basic Structure of C Program

Q6. Write the use of continue statement.

Ans: continue statement is used to go to the top of the loop from anywhere within the loop during its execution. In certain circumstances, it requires to skip a part of the body of the loop and restart from the beginning part of the loop. In such cases, continue statement is used.

Continue statement is used for continuing next iteration of loop after skipping some statement of loop. When it encountered control automatically passes through the beginning of the loop.

The continue statement can be used only inside a looping statement. It is usually associated with if statement. It is useful when we want to continue the program without executing any part of the program.

The difference between break and continue is, when the break encountered loop is terminated and it transfer to the next statement and when continue is encounter control come back to the beginning position.

Syntax:      continue;

for(initialization; test condition; modifier expression)

{

…………………..

if(condition)

continue;

……….

}

Example:

for(i=1;i<=6;i++)

{

if(i==4)

continue;

printf(“\t%d”,i);

}

Output:1    2        3        5       6

In the above example, only i=1,2,3,5,6 will be printed. When i is equal to 4, control returns to the beginning of the loop.

Q7. What is a flowchart?  Draw the flowchart for maximum of two numbers.

Ans: Flowchart in C is a diagrammatic representation of a sequence of logical steps of a program. It uses various symbols to show the operations and decisions to be followed in a program

A flowchart is a graphical depiction of decisions and the results of those decisions. Programmers often use it as a program-planning tool to solve a problem. It makes use of symbols that are connected among them to indicate the flow of information and processing. The process of drawing a flowchart for an algorithm is known as “flowcharting”.

Flowchart for maximum of two numbers:

Q8. Why do we use #define in our program?

Ans: #define directive is used to define constants or an expression in our program.

The #define preprocessor directive lets a programmer or a developer define the macros within the source code.

In the C Programming Language, the #define directive allows the definition of macros within our source code. These macro definitions allow constant values to be declared for use throughout our code.

One of the common ways to define constants in C is to use the # define preprocessor directive.

The syntax for creating a constant using #define in the C language is:

Syntax:

#define CNAME value

OR

#define CNAME expression

Where CNAME = name of the constant

Examples:

Defining a value:

#define MAX 10

Defining an expression:

#define SUM(a,b) a+b

Q9. What is the use of ‘\n’?

Ans: ‘\n’ is a Escape Sequence which produces a new line. It performs newline i.e. it moves the cursor to next line. 

For example:

Consider two statements:

printf(“Hello!”);

printf(“ Welcome to India.”);

The output of these statements is:

Hello! Welcome To India.

If we want the second printf() to produce its message in the next line, then we have to use the new line character ‘\n’.

printf(“Hello!”);

printf(“\n Welcome to India.”);

The Output will be:

Hello!

Welcome to India.

 

If you don't include the ‘\n’, the next print statement will continue on the same line.

Q10. What is call by call by value and call by reference?

Ans: Call by value and call by reference is type of function calls. In C language, these two methods are used to pass the data into the function

 

Functions can be invoked in two ways: Call by Value or Call by Reference.

Call by value:

When a function is called by value, a copy of the actual parameter is created and sent to the formal parameter of the called function. The called function uses only the copy of the actual parameter. Therefore, the value of the actual parameter cannot be altered by the called function. Any changes made inside called function are not reflected in actual parameters of the calling function.

Call by reference:

When a function is called by reference, the address of the actual parameters is sent to the formal parameter of called functions. If we make any change in the formal parameters, it shows the effect in the value of the actual parameter.

When parameters are passed to a function, the parameters are passed by value. That is a copy of the actual parameter is sent to the called function. Therefore, called function cannot change the value of the actual parameter of the calling function. But, there might be some cases where we need to change the values of actual parameter in the calling function.

In order to enable the called function to change the variable of the calling function, the address of the actual parameter must be passed. When a parameter is passed by reference, we are not passing copy of its value, but we are passing the parameter itself to the called function. Any changes made inside the called functions are actually reflected in actual parameters of the calling function. The called function can alter the value of the actual parameters.

Q11. Why floating point numbers are not used for equality in expressions?

Ans: In the case of floating-point numbers, the relational operator(==) does not produce correct output, this is due to the internal precision errors in rounding up floating-point numbers.

The equality operators (= = and !=) are much more troublesome. The = = operator, returns true only if its operands are exactly equal. Because even the smallest rounding error will cause two floating point numbers to not be equal, operator= = is at high risk for returning false when a true might be expected. Operator!= has the same kind of problem.

For this reason, use of these operators with floating point operands should be avoided.

Q12. How does type float differ from double in C programming?

Ans:  Float and double are both widely used data types in programming that have the ability to store decimal or floating-point numbers. Though Float and Double both of them are used for assigning real (or decimal) values, there are some differences between these two data types.

 

FLOAT	DOUBLE
It has single precision data-type.	It has double precision data type or we can say two times more precision than float.
Float data types can store up to 7 digits.	Double data type can store up to 15 digits
The format specifier for float is %f.	The format specifier for double is %lf.
It is a 32-bit floating-point data type.	It is a 64-bit floating-point data type.
It takes 4-bytes of memory space.	It takes 8-bytes of memory space.
It has 6-digits of precision.	It has 15-digits of precision.
A value having a range within 1.2E-38 to 3.4E+38 can be assigned to float variables.	A value having range within 2.3E-308 to 1.7E+308 can be assigned to double type variables

Q13. What is null string?

Ans: A null ring has no values at all. It is represented by null. It is an empty char array, one that has not been assigned any elements. The string exists in memory, so its not a null pointer. It’s just absent any elements.

 

Q14. What is null pointer?

Ans: A pointer variable that is initialized with the NULL value at the time of pointer declaration is called Null pointer. A Null pointer is a pointer which points nowhere, it doesn't have an address of any function or a variable.

The Null pointer doesn’t point to any memory location. We can specify any of the following values for a null pointer constant:

• 0
• NULL

 

Syntax:

datatype *var_name= NULL;

Q15. Explain in brief the nested if statement?

Ans: In C programming, if statement may itself contain another if statement. When if statement comes within another if statement then this is known nested if statement.

Nested if statement is placing if statement inside another if statement. Nested if in C is helpful if we want to check the condition inside a condition.

If outer if statement fails, then the compiler skips the entire block irrespective of their inner if statement.

The following example illustrates the nested if statement.

if(x>=3)

{

if(x<=5)

printf(“ The number lies between 3 and 5”);

}

else

printf(“The number does not lie between 3 and 5”);

Q16: What is “sizeof” operator?

Ans: The sizeof operator is a much used operator in C. It is a compile time unary operator which can be used to compute the size of its operand. It returns the size of a variable. It can be applied to any data type, float type, pointer type variables.

The sizeof operator gives the amount of storage, in bytes, required to store an object of the type of the operand. When sizeof() is used with the data types, it simply returns the amount of memory allocated to that data type.

sizeof is greatly used in dynamic memory allocation.

Syntax:

sizeof(type_name)

Example: 

sizeof(int)    returns 2, since an integer occupies 2 bytes of memory

Q17. What is a register variable in C?

Ans: Register variables tell the compiler to store the variable in CPU register instead of memory. Registers are faster than memory to access, so the variables which are most frequently used in a C program can be put in registers. “register” keyword is used to declare the register variables. The keyword register hints to compiler that a given variable can be put in a register.

Syntax:

register data_type var_name;

Example:

register int i;

Q18. What do you mean by unary operators?
               Or
 Define unary operators.

Ans: C has a type of operators that act upon a single operand to produce a new value. These types of operators are known as unary operators. Unary operators generally precede their single operands, though some unary operators are written after their operands.

A unary operator is an operator used to operate on a single operand to return a new value. All the unary operators have equal precedence, and their associativity is from right to left. When we combine the unary operator with an operand , we get the unary expression.

Q19. What are the basic data types available in C?

Ans: The basic data types available in C are:

• Integer data type (int)
• Floating point type (float)
• Character data type (Char)

Q20. What is the use of goto statement?

Ans: The goto statement is used to alter the normal flow of control in a program. This statement transfers control to any part of the program unconditionally. In certain cases, we may require to transfer control to the other part of the program. C provides goto statement to jump unconditionally from one part to another part of the program. This helps in controlling the flow of execution based on certain specific condition.

Q21. Write the difference between while loop and do-while loop.

Ans: Differences between while loop and do-while loop:

Basis for comparison	While loop	Do-while loop
Controlling condition	The controlling condition appears at the beginning of the loop.	The controlling condition appears at the end of the loop.
Checking condition	The condition is  checked first and then loop body is executed	The loop body is executed first and then the condition is checked.
Loop Type	It is entry-controlled loop	It is exit-controlled loop
Semicolon	No semicolon at the end of while. while (condition)	Semicolon at the end of the while. while (condition);
Loop execution	The loop body would be executed only if the given condition is true. Statement(s) is executed zero times if condition is false.	The loop body would be executed at least once even the given condition is false.
Initialization of variable	Variable in condition is initialized before the execution of loop body.	Variable may be initialized before or within the loop body.
Requirement of Brackets	If there is a single statement, brackets are not required.	Brackets are always required.
Syntax	while(condition) { statements;//Body of the loop }	do { statements;//Body of the loop } while(condition);
Iteration	The iterations do not occur if, the condition at the first iteration appears false.	The iteration occurs at least once even if the condition is false at the first iteration.