C Language: Question Bank

Material from Interview Mantra. Subscribe to free updates via email. Material from Interview Mantra. Subscribe to free updates via email. Favourite 50 – C Interview Question Bank for freshers and experienced IT programmers Written by Madhulika Reddy and Dhoka Ratan. Edited and Published by Sridhar Jammalamadaka Get the latest updates and news on topics Career and Education from Interview Mantra – Subscribe to Interview Mantra for free. ABOUT THIS BOOK This book comprises of Interview Questions and Answers collected from the famous career advice blog www. InterviewMantra. et The aim of this book is to help freshers and experienced programmers to quickly brush up the basic concepts of C language. This book can be used as a quick study guide before attending a job interview which requires knowledge of C programming language. The questions that appear in this book are few of the most frequently asked questions in IT Job interviews in top MNC companies. All the questions hav e been neatly answered and have been supported with example code wherever applicable. A lot of effort has been put into this book to make the answers as accurate as possible, but no warranty or fitness is implied. The authors and the publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the programs accompanying it. Please send your feedback to us via email to [email  protected] net COPYRIGHT INFO C language – Interview Question Bank by Sridhar Jammalamadaka is licensed under a Creative Commons Attribution-Share Alike 2. 5 India License. Based on a work at www. interviewmantra. net. In simple words, you may use this work for commercial purposes, remix the work, reproduce it by any means, provided ou keep a link to http://www. interviewmantra. net and attribute the work to the owner – Sridhar Jammalamadaka. CONTENTS AT A GLANCE 1. 2. 3. 4. 5. Chapter Name pg-no Variables & Control Flow . . . . . . . . . . . . . . . . . . . . 6 Operators, Constants & Structures . . . . . . . . . . . .11 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 Material from Interview Mantra. Subscribe to free updates via email. TABLE OF CONTENTS CHAPTER 1: Variables & Control Flow 1. What is the difference between declaring a variable and defining a variable? 2. What is a static variable? 3. What is a register variable? 4. Where is an auto variable stored? 5. What is scope & storage allocation of extern and global variables? 6. What is scope & storage allocation of register, static and local variables? 7. What are storage memory, default value, scope and life of Automatic and Register storage class? 8. What are storage memory, default value, scope and life of Static and External storage class? 9. What is the difference between ‘break' and ‘continue' statements? 0. What is the difference between ‘for' and ‘while' loops? CHAPTER 2: Operators, Constants & Structures 1. Which bitwise operator is suitable for checking whether a particular bit is ON or OFF? 2. Which bitwise operator is suitable for turning OFF a particular bit in a number? 3. What is equivalent of multiplying an unsigned int by 2: left shif t of number by 1 or right shift of number by 1? 4. What is an Enumeration Constant? 5. What is a structure? 6. What are the differences between a structure and a union? 7. What are the advantages of unions? 8. How can typedef be to define a type of structure? 9. Write a program that returns 3 numbers from a function using a structure. 10. In code snippet below: struct Date { int yr; int day; int month; } date1,date2; date1. yr = 2004; date1. day = 4; date1. month = 12; Write a function that assigns values to date2. Arguments to the function must be pointers to the structure, Date and integer variables date, month, year. Material from Interview Mantra. Subscribe to free updates via email. CHAPTER 3: Functions 1. What is the purpose of main() function? 2. Explain command line arguments of main function? 3. What are header files? Are functions declared or defined in header files ? 4. What are the differences between formal arguments and actual arguments of a function? 5. What is pass by value in functions? 6. What is pass by reference in functions? 7. What are the differences between getchar() and scanf() functions for reading strings? 8. Out of the functions fgets() and gets(), which one is safer to use and why? 9. What is the difference between the functions strdup() and strcpy()? CHAPTER 4: Pointers 1. What is a pointer in C? 2. What are the advantages of using pointers? 3. What are the differences between malloc() and calloc()? 4. How to use realloc() to dynamically increase size of an already allocated array? . What is the equivalent pointer expression for referring an element a[i][j][k][l], in a four dimensional array? 6. Declare an array of three function pointers where each function receives two integers and returns float. 7. Explain the variable assignment in the declaration int *(*p[10])(char *, char *); 8. What is the value of sizeof(a) /sizeof(char *) in a code snippet: char *a[4]={â€Å"sridhar†,†raghava†,†shashi†,†srikanth†}; 9. (i) What are the differences between the C statements below: char *str = â€Å"Hello†; char arr[] = â€Å"Hello†; (ii) Whether following statements get complied or not? Explain each statement. arr++; *(arr + 1) = ‘s'; printf(â€Å"%s†,arr); CHAPTER 5: Programs 1. Write a program to find factorial of the given number. 2. Write a program to check whether the given number is even or odd. 3. Write a program to swap two numbers using a temporary variable. 4. Write a program to swap two numbers without using a temporary variable. Material from Interview Mantra. Subscribe to free updates via email. 5. Write a program to swap two numbers using bitwise operators. 6. Write a program to find the greatest of three numbers. 7. Write a program to find the greatest among ten numbers. . Write a program to check whether the given number is a prime. 9. Write a program to check whether the given number is a palindromic number. 10. Write a program to check whether the given string is a palindrome. 11. Write a program to generate the Fibonacci series. 12. Write a program to print â€Å"Hello World† without using semicolon anywhere in the code. 13. Wr ite a program to print a semicolon without using a semicolon anywhere in the code. 14. Write a program to compare two strings without using strcmp() function. 15. Write a program to concatenate two strings without using strcat() function. 16. Write a program to delete a specified line from a text file. 17. Write a program to replace a specified line in a text file. 18. Write a program to find the number of lines in a text file. 19. Write a C program which asks the user for a number between 1 to 9 and shows the number. If the user inputs a number out of the specified range, the program should show an error and prompt the user for a valid input. 20. Write a program to display the multiplication table of a given number. Testimonials Anushka M says â€Å"Thank you soooo much for all these questions, along with the solutions. It’s a great compilation. Thanks a lot guys. 🙂 † Anonymous says â€Å"Awesome. Thanks a ton for uploading this pdf, your concept was crystal clear. Now I am very confident about myself. Now I'm ready to face the interview challenge. Thanks once again. † Urmi says â€Å"Thank You.. It's Nice.. It saved my valuable Time.. Thanks a lot! † Rajakumari says â€Å"Thank you so †¦ much Mr. Sridhar. No words to say , lot of thanks†¦Ã¢â‚¬ ¦ Very useful to freshers & experienced. † Material from Interview Mantra. Subscribe to free updates via email. CHAPTER 1: Variables & Control Flow 1. What is the difference between declaring a variable and defining a variable? Declaration of a variable in C hints the compiler about the type and size of the variable in compile time. Similarly, declaration of a function hints about type and size of function parameters. No space is reserved in memory for any variable in case of declaration. Example: int a; Here variable ‘a' is declared of data type ‘int' Defining a variable means declaring it and also allocating space to hold it. We can say â€Å"Definition = Declaration + Space reservation†. Example: int a = 10; Here variable â€Å"a† is described as an int to the compiler and memory is allocated to hold value 10. 2. What is a static variable? A static variable is a special variable that is stored in the data segment unlike the default automatic variable that is stored in stack. A static variable can be initialized by using keyword static before variable name. Example: static int a = 5; A static variable behaves in a different manner depending upon whether it is a global variable or a local variable. A static global variable is same as an ordinary global variable except that it cannot be accessed by other files in the same program / project even with the use of keyword extern. A static local variable is different from local variable. It is initialized only once no matter how many times that function in which it resides is called. It may be used as a count variable. Example: #include //program in file f1. c void count(void) { static int count1 = 0; int count2 = 0; count1++; count2++; printf(â€Å"Value of count1 is %d, Value of count2 is %d†, count1, count2); } /*Main function*/ int main(){ count(); count(); count(); return 0; } Output: Value of count1 is 1, Value of count2 is 1 Value of count1 is 2, Value of count2 is 1 Material from Interview Mantra. Subscribe to free updates via email. Value of count1 is 3, Value of count2 is 1 3. What is a register variable? Register variables are stored in the CPU registers. Its default value is a garbage value. Scope of a register variable is local to the block in which it is defined. Lifetime is till control remains within the block in which the register variable is defined. Variable stored in a CPU register can always be accessed faster than the one that is stored in memory. Therefore, if a variable is used at many places in a program, it is better to declare its storage class as register Example: register int x=5; Variables for loop counters can be declared as register. Note that register keyword may be ignored by some compilers. . Where is an auto variables stored? Main memory and CPU registers are the two memory locations where auto variables are stored. Auto variables are defined under automatic storage class. They are stored in main memory. Memory is allocated to an automatic variable when the block which contains it is called and it is de-allocated at the completion of its block execution. Auto variables: Storage : main memory. Default value : garbage value. Scope : local to the block in which the variable is defined. Lifetime : till the control remains within the block in which the variable is defined. 5. What is scope & storage allocation of extern and global variables? Extern variables: belong to the External storage class and are stored in the main memory. extern is used when we have to refer a function or variable that is implemented in other file in the same project. The scope of the extern variables is Global. Example: /*************** Index: f1. c ****************/ #include extern int x; int main() { printf(â€Å"value of x %d†, x); return 0; } Index: f2. c ****************/ int x = 3; Here, the program written in file f1. c has the main function and reference to variable x. The file f2. c has the declaration of variable x. The compiler should know the datatype of x and this is done by extern definition. Material from Interview Mantra. Subscribe to free updates via email. Global variables: are variables which are declared above the main( ) function. These variables are accessible throughout the program. They can be accessed by all the functions in the program. Their default value is zero. Example: #include int x = 0; /* Variable x is a global variable. It can be accessed throughout the program */ void increment(void) { x = x + 1; printf(† value of x: %d†, x); } int main(){ printf(† value of x: %d†, x); increment(); return 0; } 6. What is scope & storage allocation of register, static and local variables? Register variables: belong to the register storage class and are stored in the CPU registers. The scope of the register variables is local to the block in which the variables are defined. The variables which are used for more number of times in a program are declared as register variables for faster access. Example: loop counter variables. register int y=6; Static variables: Memory is allocated at the beginning of the program execution and it is reallocated only after the program terminates. The scope of the static variables is local to the block in which the variables are defined. Example: #include void decrement(){ static int a=5; a–; printf(â€Å"Value of a:%d†, a); } int main(){ decrement(); return 0; } Here ‘a' is initialized only once. Every time this function is called, ‘a' does not get initialized. so output would be 4 3 2 etc. , Local variables: are variables which are declared within any function or a block. They can be accessed only by function or block in which they are declared. Their default value is a garbage value. 7. What are storage memory, default value, scope and life of Automatic and Register storage class? . Automatic storage class: Storage : Default value : main memory. garbage value. Material from Interview Mantra. Subscribe to free updates via email. Scope Lifetime Storage Default value Scope Lifetime : : : : : : local to the block in which the variable is defined. till control remains within the block. CPU registers. ga rbage value. local to the block in which the variable is defined. till control remains within the block. 2. Register storage class: 8. What are storage memory, default value, scope and life of Static and External storage class? 1. Static storage class: Storage Default value Scope Lifetime Storage Default value Scope Lifetime : : : : : : : : main memory. zero local to the block in which the variable is defined. till the value of the variable persists between different function calls. main memory zero global as long as the program execution doesn't come to an end. 2. External storage class: 9. What is the difference between ‘break' and ‘continue' statements? Differences between ‘break' and ‘continue' statements break 1. break is a keyword used to terminate the loop or exit from the block. The control jumps to next statement after the loop or block. 2. Syntax: { Statement 1; Statement 2; Statement n; break; } 3. reak can be used with for, while, do- while, and switch statements. When break is used in nested loops i. e. within the inner most loop then only the innermost loop is terminated. 4. Example: i = 1, j = 0; while(i a && b ; c) { printf(â€Å"b is Greater than a and c†); } else if (c ; a && c ; b) { printf(â€Å"c is Greater than a and b†); } else { printf(â€Å"all are equal or any two values are equal†); } return 0; } Output: Enter a,b,c: 3 5 8 c is Greater than a and b Explanation with examples: Consider three numbers a=5,b=4,c=8 if(a;b && a;c) then a is greater than b and c now check this condition for the three numbers 5,4,8 i. . if(5;4 && 5;8) /* 5>4 is true but 5>8 fails */ so the control shifts to else if condition else if(b;a && b;c) then b is greater than a and c now checking this condition for 5,4,8 i. e. else if(4;5 && 4;8) /* both the conditions fail */ now the control shifts to the next else if condition else if(c;a && c;b) then c is greater than a and b Material from Interview Mantra. Subscribe to free updates via email. now checking this condition for 5,4,8 i. e. else if(8;5 && 8;4) /* both conditions are satisfied */ Thus c is greater than a and b. 7. Write a program to find the greatest among ten numbers. Program: #include int main() { int a[10]; int i; int greatest; printf(â€Å"Enter ten values:†); //Store 10 numbers in an array for (i = 0; i ; 10; i++) { scanf(â€Å"%d†, [i]); } //Assume that a[0] is greatest greatest = a[0]; for (i = 0; i ; 10; i++) { if (a[i] ; greatest) { greatest = a[i]; } } printf(â€Å"Greatest of ten numbers is %d†, greatest); return 0; } Output: Enter ten values: 2 53 65 3 88 8 14 5 77 64 Greatest of ten numbers is 88 Explanation with example: Entered values are 2, 53, 65, 3, 88, 8, 14, 5, 77, 64 They are stored in an array of size 10. et a[] be an array holding these values. /* how the greatest among ten numbers is found */ Let us consider a variable ‘greatest'. At the beginning of the loop, variable ‘greatest' is assinged with the value of first element in the array greatest=a[0]. Here variable ‘greatest' is assigned 2 as a[0]=2. Below loop is executed until end of the array ‘a[]';. for(i=0; igreatest) { greatest= a[i]; } } For each value of ‘i', value of a[i] is compared with value of variable ‘greatest'. If any value greater than the value of ‘greatest' is encountered, it would be replaced by a[i]. After completion of ‘for' loop, the value of variable ‘greatest' holds the greatest number in the array. In this case 88 is the greatest of all the numbers. Material from Interview Mantra. Subscribe to free updates via email. 8. Write a program to check whether the given number is a prime. A prime number is a natural number that has only one and itself as factors. Examples: 2, 3, 13 are prime numbers. Program: #include main() { int n, i, c = 0; printf(â€Å"Enter any number n: â€Å"); scanf(â€Å"%d†, ); /*logic*/ for (i = 1; i