In this tutorial, we will discuss C interview questions with their answers. These questions are from the core and important concepts of the C programming language. To attempt these questions rightly, you will have to master the basic concepts of the C programming language.<\/p>\n
We have divided the C Interview question answers into 3 parts as C Interview questions for beginners, C Programming Interview Questions for intermediate and Advance C Language Interview Questions.<\/p>\n
If you read through these questions and also give the right answers to these following questions then it will help you to prepare better for placement and interviews. These questions are based on different types of concepts in C. It will help you in getting placed at big companies such as TCS, Infosys, Wipro, Accenture etc.<\/p>\n
Below are the C interview questions with answers for beginners.<\/p>\n
Q.1<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> 15<\/p>\n Q.2<\/strong> What is the use of \u2018\\b\u2019 in the following program?<\/p>\n Ans.<\/strong> The \u2018\\b\u2019<\/strong> is an escape sequence that is used to move the cursor backwards. It normally does what backspace does on your keyboard. The above will print Advance<\/strong> to the screen.<\/p>\n Q.3<\/strong> If you open a file through the fopen() function then which parameters will fseek() require to work with that file?<\/p>\n Ans.<\/strong> First, the number of bytes to search for. Second, the point of origin of that file and third, a file pointer to that file.<\/p>\n fopen() function<\/strong> Syntax<\/strong><\/p>\n The function returns null if the execution does not succeed and if it succeeds then it returns a pointer to FILE.<\/p>\n fseek() function<\/strong> Syntax<\/strong><\/p>\n Q.4<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> 13<\/p>\n Q.5<\/strong> Suppose, a block of memory is allocated. Can you free that block of memory which is allocated? If yes, how?<\/p>\n Ans.<\/strong> Yes, you can free the previously allocated block of memory with the help of free() function.<\/p>\n free() function in C<\/strong> Declaration<\/strong><\/p>\n Example:-<\/strong><\/p>\n Output:-<\/strong> Q.6<\/strong> In C programs, why is it a bad practice to make use of the gets() function?<\/p>\n Ans.<\/strong> The problem in using the gets() function is that it does not know how big the buffer is. That\u2019s why it continues to read until it finds a newline or encounters EOF and it may result in buffer overflow.<\/p>\n gets() function<\/strong> Declaration<\/strong><\/p>\n Example:-<\/strong><\/p>\n Output:-<\/strong> Q.7<\/strong> Why is the following program dangerous?<\/p>\n Ans.<\/strong> In that above program, we pass an attacker-controlled buffer as an argument to a printf() function. With this, the attacker can perform writing to arbitrary memory addresses. You must use the format string to determine the number of arguments in the printf() function.<\/p>\n Q.8<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> 9<\/p>\n Q.9<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> 6.000000<\/p>\n Q.10<\/strong> Can you tell me the errors that occurred on the following program?<\/p>\n Ans.<\/strong> The function add() is not defined and there is no semicolon at the end of the printf() function.<\/p>\n Q.11<\/strong> In any C program, can you execute that program without including any header files into it?<\/p>\n Ans.<\/strong> In some compilers, yes you can. But it will give you a warning to include the following header file to the program code. But in some compilers, you can\u2019t. Because you will have to include a header file named stdio.h.<\/strong> Example:-<\/strong><\/p>\n Output:-<\/strong> Q.12<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> A<\/p>\n Q.13<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> Have a good day!!<\/p>\n Q.14<\/strong> Can you tell me the ways to convert a string to integer value?<\/p>\n Ans. First Method:-<\/strong> Declaration<\/strong><\/p>\n Example:-<\/strong><\/p>\n Output:-<\/strong> Second Method:-<\/strong> Declaration<\/strong><\/p>\n Example:-<\/strong><\/p>\n Q.15<\/strong> Suppose, you included the same header files twice in your program. Then, how can you avoid including the same header files twice in your program code?<\/p>\n Ans.<\/strong> You can make use of the ifndef and define preprocessor directives. Suppose, the header file is header.h then you can include the header file like below:-<\/p>\n In the above, the ifndef will check if the header.h is defined or not. If it is not then it will define the header.h file.<\/p>\n Q.16<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> The above program will print the Hi, John Here!<\/strong> text infinitely.<\/p>\n Q.17<\/strong> Can you tell the difference between const char* ptr and char const* ptr?<\/p>\n Ans.<\/strong><\/p>\n NOTE:-<\/strong> A pointer should always point to the same address but the value at the location is changed.<\/p>\n const char* ptr<\/strong> Example:-<\/strong><\/p>\n Output:-<\/strong> char const* ptr<\/strong> Example:-<\/strong><\/p>\n Output:-<\/strong> Q.18<\/strong> How can you allocate a single block of memory dynamically in the C programming language?<\/p>\n Ans.<\/strong> In C, you can make use of malloc() function to allocate a single block of memory dynamically in C. This function is defined in the stdlib.h<\/strong> header file. It returns a pointer to the allocated memory.<\/p>\n Syntax of malloc()<\/strong><\/p>\n Example:-<\/strong><\/p>\n Output:-<\/strong> Q.19<\/strong> Suppose, you created a file named Tech.txt. Then what will be the name of that file after executing the below program?<\/p>\n Ans.<\/strong> random<\/p>\n Q.20<\/strong> Can you tell me the errors occurred on the following program?<\/p>\n Ans.<\/strong> The function add() is not defined and there is no semicolon at the end of the printf() function.<\/p>\n Q.21<\/strong> Write a code to print the following pattern?<\/p>\n #### Ans.<\/strong><\/p>\n Q.22<\/strong> What is the output of the following program?<\/p>\n Ans.<\/strong> Book! 14<\/p>\n Q.23<\/strong> You can include header files into the C program in 2 ways using <> and \u201c\u201d. What is the difference between <> and \u201c\u201d?<\/p>\n Ans.<\/strong> If you declare the header file using <> then the compiler will search for that header file in the built-in library. But if you declare the header file using \u201c\u201d then the compiler will search for that header file in the current working directory.<\/p>\n We have created our own header file named header.h.<\/p>\n header.h<\/strong><\/p>\n Below is the source code which uses the header file:-<\/p>\n Output:-<\/strong> Q.24<\/strong> In C, can you add pointers to each other?<\/p>\n Ans.<\/strong> No, you cannot add pointers together. It is not possible. Pointers contain addresses and you cannot retrieve the value out of this operation. If you add addresses then it won\u2019t make sense. But you can subtract two addresses to find the offset between those addresses. It is a very useful one. You can also crash the code by adding pointers or it can result in overflow.<\/p>\n Q.25<\/strong> Is it possible to print a string with the % symbol in it? If yes, how?<\/p>\n Ans.<\/strong> Yes, you can.<\/p>\n Q.26<\/strong> Can you tell what the below statement is doing?<\/p>\n Ans.<\/strong> \u201cREAL a\u201d is used to define a type int. \u201cREALP *b\u201d would define pointer b of type int **. \u201cONE a1\u201d would define a1 as an array of 10 int.<\/p>\n Q.27<\/strong> Can you describe what the below expression is doing?<\/p>\n Ans.<\/strong> The above expression will create an array arr<\/strong> of 1 element. Then each of the elements of arr contain a struct field of int array of 3 elements. arr[0].a[0] is 2, arr[1].a[1] is 1 and arr[2].a[2] is 3. There is nothing wrong with the expression.<\/p>\n Q.28<\/strong> Is the below expression correct?<\/p>\n Ans.<\/strong> Yes, the above expression is correct. The above statement will initialize arr[1], arr[2], arr[3] \u2026, arr[38], arr[39], arr[40] to 1,2,3,4,…,38,39,40. And the remaining elements of that array will be initialized to 0.<\/p>\n Q.29<\/strong> What is the output of the below program code?<\/p>\n Ans.<\/strong> 5<\/p>\n Q.30<\/strong> For comparing strings in C, can you use the if function?<\/p>\n Ans.<\/strong> No, you cannot use the if function to compare strings. It is only used to compare numeric and single character values. For comparing strings, you can use the strcmp() function.<\/p>\n Declaration<\/strong><\/p>\n If the return value of the function is less than 0 then s1 is less than s2 and if it is greater than 0 then s2 is less than s1. And it is equal to 0 then s1 and s2 both are the same.<\/p>\n Example:-<\/strong><\/p>\n Output:-<\/strong> Q.31<\/strong> Are the uninitialized pointer and the null pointer the same in C?<\/p>\n Ans.<\/strong> Null pointer is a pointer which points to nothing. Value of the null pointer is 0. Below we made a pointer to point to null:-<\/p>\n The uninitialized pointer is also known as a wild pointer. This pointer points to an arbitrary memory location. It is a bad practice to use the uninitialized pointer. It can have a valid pointer value in it.<\/p>\n Example:- null pointer<\/strong><\/p>\n The above program will not print anything back to the screen because of the null pointer.<\/p>\n Example:- uninitialized pointer<\/strong><\/p>\n Q.32<\/strong> What will be the output of the following program?<\/p>\n Ans.<\/strong> 6c<\/p>\n Q.33<\/strong> What is the output of the following program?<\/p>\n#include <stdio.h>\nint main(void)\n{\nint data;\nint val= 1;\nint arr[4] = { 2, 3, 1, 4};\ndata = 4 * 4 + arr[val++] - (9 \/ val);\nprintf(\"%d\", data);\nreturn 0;\n}\n<\/pre>\n#include <stdio.h>\nint main(void)\n{\nprintf(\"Advance\\be\");\nreturn 0;\n}\n<\/pre>\n
\nThe main purpose of the fopen() function is to open a file to perform several operations which includes reading, writing, editing etc.<\/p>\nFILE *fopen(const char *filename, const char *operation_mode);\n<\/pre>\n
\nThe main purpose of the fseek() function is to set the file pointer of the stream to a given offset. To put it short, you can use this function for writing data into a file at a specified location.<\/p>\nint fseek(FILE *stream, long int offset, int pos) \n<\/pre>\n
#define add(data) data+data\nint main()\n{\nint data;\ndata = 36\/add(10);\nprintf(\"%d\",data);\nreturn 0;\n}\n<\/pre>\n
\nThe free() function is mainly used to deallocate a block of memory which was allocated previously. It calls malloc, calloc or realloc to perform the task. And it does not return any value.<\/p>\nvoid free(void *pointer)\n<\/pre>\n
#include <stdio.h>\n#include <stdlib.h>\n#include <string.h>\n\nint main () {\n char *st;\n\n st = (char *) malloc(20);\n strcpy(st, \"C\");\n printf(\"%s => %u\\n\", st, st);\n\n st = (char *) realloc(st, 20);\n strcat(st, \" Quiz\");\n printf(\"%s => %u\", st, st);\n free(st);\n \n return(0);\n}\n<\/pre>\n
\nC => 27021328
\nC Quiz => 27021328<\/p>\n
\nIt reads a line from stdin and it stores the line into the string that is pointed by the str. It is a bad practice to use the gets() function in your program code. Because it keeps reading the line until it reaches a newline character.<\/p>\nchar *gets(char *str)\n<\/pre>\n
#include <stdio.h>\n\nint main () {\n char st[50];\n\n printf(\"Enter something: \");\n gets(st);\n printf(\"%s\", st);\n return(0);\n}\n<\/pre>\n
\nEnter something: Nice Day
\nNice Day<\/p>\n#include<stdio.h>\nint main(int argc, char** argv)\n{\nchar buffer[100];\nstrncpy(buffer, argv[1], 100);\nprintf(buffer);\nreturn 0;\n}\n<\/pre>\n#include <stdio.h>\nint main()\n{\n int arr[3] = {2,5,9};\n int *pt = (int*)(&arr+1);\n printf(\"%d\",*(pt-1));\n return 0;\n}\n<\/pre>\nint main(){\nfloat d ;\nint a=20,b=3;\nd = ( int ) a \/ b ;\nprintf(\"%f\",d);\nreturn 0;\n}\n<\/pre>\n#include <stdio.h>\nint main()\n{\nint b=20,a=20;\nint res = add(b,a);\nprintf(\"%d\",res)\nreturn 0;\n}\n<\/pre>\n
\nIf you are using some predefined functions such as free(), strcat(), time() etc then you have to use their own header files in which they are defined.<\/p>\nint printf(const char *format, ...);\nint main()\n{\n printf( \"Have a nice day!\" );\n return 0;\n}\n<\/pre>\n
\nHave a nice day!<\/p>\nint main()\n{\n char *point = \"Amen\";\n printf(\"%c\", *&*&*point);\n return 0;\n}\n<\/pre>\n#include <stdio.h>\nint main()\n{\nwhile (printf(\"Have a good day!\"))\nreturn 0;\n}\n<\/pre>\nIntermediate Level C Interview Questions<\/h3>\n
\nYou can use the existing atoi() function in C. The main purpose of this is to convert the string argument to an integer.<\/p>\nint data = atoi(string1);\n<\/pre>\n
#include <stdio.h>\n#include <stdlib.h>\n#include <string.h>\n\nint main () {\n int data;\n char st[20];\n strcpy(st, \"123\");\n data = atoi(st);\n printf(\"%d\",data);\n\n return(0);\n}\n<\/pre>\n
\n123<\/p>\n
\nYou can also use the sscanf() function. The main purpose of this function is to read formatted input from a string.<\/p>\nint sscanf(const char *str, const char *format, ...)\n<\/pre>\n
sscanf(string1,\u201d%d\u201d,&data)\n<\/pre>\n
#ifndef header.h\n#define header.h\n#endif\n<\/pre>\n
#include<stdio.h>\nint main()\n{\n for(;;)\n printf(\"Hi, John Here!\");\n return 0;\n}\n<\/pre>\n
\nThe character is pointed by the pointer variable ptr. You cannot change the value but you can initialize the ptr with another memory location.<\/p>\n#include<stdio.h>\n#include<stdlib.h> \nint main()\n{\n char x ='X', y ='Y';\n const char *pt = &x;\n printf( \"The value pointed by pt-> %c\\n\", *pt);\n pt = &y;\n printf( \"The value pointed by pt-> %c\\n\", *pt);\n}\n<\/pre>\n
\nThe value pointed by pt-> X
\nThe value pointed by pt-> Y<\/p>\n
\nThe pointer ptr is constant. You cannot assign ptr with another memory location but you can change the value of the character pointed by ptr.<\/p>\n#include<stdio.h>\n#include<stdlib.h> \nint main()\n{\n char x ='X', y ='Y';\n char *const pt = &x;\n printf( \"The value pointed by pt: %c\\n\", *pt);\n printf( \"pointing to: %d\\n\", pt);\n *pt = y;\n printf( \"The value pointed by pt: %c\\n\", *pt);\n printf( \"pointing to: %d\\n\", pt);\n}\n<\/pre>\n
\nThe value pointed by pt: X
\npointing to: 936799398
\nThe value pointed by pt: Y
\npointing to: 936799398<\/p>\nptr = (cast-type*) malloc(byte-size)\n<\/pre>\n
#include <stdio.h>\n#include <stdlib.h>\n#include <string.h>\n\nint main () {\n char *st;\n\n st = (char *) malloc(20);\n strcpy(st, \"Good\");\n printf(\"%s => %u\\n\", st, st);\n\n st = (char *) realloc(st, 20);\n strcat(st, \" Day\");\n printf(\"%s => %u\", st, st);\n free(st);\n \n return(0);\n}\n<\/pre>\n
\nGood => 36782096
\nGood Day => 36782096<\/p>\n#include <stdio.h>\nint main()\n{\nint res;\nchar o[] = \"Tech.txt\";\nchar n[] = \"random.txt\";\nres = rename(o, n);\nif (res == 0)\nputs(\"success\");\nelse\nperror(\"Error\");\nreturn 0;\n}\n<\/pre>\n#include <stdio.h>\nint main()\n{\nint b=20,a=20;\nint res = add(b,a);\nprintf(\"%d\",res)\nreturn 0;\n}\n<\/pre>\n
\n###
\n##
\n#<\/p>\n#include <stdio.h>\nint main() {\nint i, j, rows=4;\nfor (i = rows; i >= 1; --i) {\nfor (j = 1; j <= i; ++j) {\nprintf(\"#\");\n}\nprintf(\"\\n\");\n}\nreturn 0;\n}\n<\/pre>\n#include <stdio.h>\nint main()\n{\ntypedef struct Tech{\nchar string[14];\nint data;\n}tech;\ntech s1, s2 = { \"B\\bBook!\", 14};\ns1 = s2;\ns1.string[0] = 't';\nprintf(\"%s %d\", s1.string, s1.data);\nreturn 0;\n}\n<\/pre>\n#ifndef header_file \n#define header_file \nint x = 22; \n#endif\n<\/pre>\n
#include <stdio.h> \n#include \"header.h\" \nint main() \n{\nprintf(\"Value of x: %d\", x); \nreturn 0; \n}\n<\/pre>\n
\nValue of x: 22<\/p>\nAdvance C Language Interview Question Answer<\/h3>\n
To print \u2018%\u2019, you have to use \u2018%%\u2019. Follow the code below:-\nprintf(\u201cThis shirt has 30%% discount!\u201d);\n<\/pre>\n
typedef int REAL, *REALP, ONE[10];\n<\/pre>\n
struct {int a[3];} arr[] = {2,1,3};\n<\/pre>\nint arr[40] = {1,2,3,[37]=38,39,40};\n<\/pre>\n#include <stdio.h>\nint fun(int num)\n{\n static int i = 1;\n if (num >= 5)\n \treturn num;\n num=num+i;\n i++;\n return fun(num);\n}\nint main(){\n int n = fun(2);\n printf(\"%d\",n);\n}\n<\/pre>\nint strcmp(const char *s1, const char *s2)\n<\/pre>\n
#include <stdio.h>\n#include <string.h>\nint main() {\n char s1[] = \"abcd\", s2[] = \"abCd\";\n int result;\n result = strcmp(s1, s2);\n printf(\"%d\\n\", result);\n return 0;\n}\n<\/pre>\n
\n1<\/p>\nint *ptr = NULL;\nchar *ptr = NULL;\n<\/pre>\n
#include <stdio.h> \nint main() \n{ \nint *ptr=NULL; \nprintf(\"value => ptr: %d\",*ptr); \nreturn 0; \n} \n<\/pre>\nint main()\n{\nint *p;\nint x = 10;\nreturn 0;\n}\n<\/pre>\n#include <stdio.h>\nint main()\n{\n int a = 0xf;\n int b = 0x63;\n printf(\"%x\",(a^b));\n return 0;\n}\n<\/pre>\n#include <stdio.h>\n#define A 20\n#define B 5\nint main()\n{\nint (*ptr)[A][B];\nprintf(\"%d\", sizeof(*ptr));\nreturn 0;\n}\n<\/pre>\n