Question 1

C standard I/O library: what does rewind(stream) do to a file stream? Choose the most accurate behavior per ISO C for a valid open stream.

Accepted Answer

Introduction / Context: The function rewind(stream) is part of the C standard I/O library. This question tests understanding of file positioning and status flags for streams opened via fopen or related functions. Given Data / Assumptions: stream is a valid FILE* opened earlier. We are using ISO C semantics for rewind. Error and end-of-file indicators may have been set previously. Concept / Approach: rewind(stream) moves the file position indicator to the beginning of the file and clears both the error and end-of-file indicators for that stream. It does not return a value. This contrasts with functions like fseek/fseeko which return status codes and can position relative to various origins. Step-by-Step Solution: 1) Call rewind(stream). 2) File position indicator becomes 0 (beginning of file). 3) Clear EOF and error flags for the stream. 4) No value is returned; to check errors you would subsequently use functions like ferror. Verification / Alternative check: Behavior mirrors fseek(stream, 0, SEEK_SET) followed by clearerr(stream), but rewind is the concise, standardized helper for this common action. Why Other Options Are Wrong: Character reverse: There is no such notion in standard C I/O. End of file: rewind goes to the start, not the end. Beginning of that line: Line concepts are not known to the stream positioning API. Common Pitfalls: Forgetting that rewind also clears EOF and error indicators. Expecting a return value to signal success or failure. Final Answer: Reposition the file pointer to beginning of file.

Question 2

C strings: which standard library function finds the last occurrence of a character in a string? Pick the correct function name used to search from the end.

Accepted Answer

Introduction / Context: This question assesses knowledge of common string functions in the C standard library, specifically how to locate characters within a NUL-terminated byte string. Given Data / Assumptions: The target is to find the last occurrence of a given character. Input is a standard C string terminated by a '\0' byte. We want the standard function provided by string.h. Concept / Approach: The correct function is strrchr(const char *s, int c). It searches for the last occurrence of c (converted to unsigned char) in the string s, including the terminating '\0' if c is '\0'. It returns a pointer to the located character or NULL if not found. Step-by-Step Solution: 1) Include <string.h>. 2) Call p = strrchr(s, ch). 3) If p != NULL, p points to the final occurrence from the right. 4) Use the pointer for slicing or index math as needed. Verification / Alternative check: Compare with strchr which finds the first occurrence; the extra 'r' in strrchr mnemonically stands for “reverse/last”. Why Other Options Are Wrong: strnchar, strchar, strrchar: These are not standard C functions. Common Pitfalls: Confusing strchr and strrchr. Forgetting that searching for '\0' is allowed and returns a pointer to the terminator. Final Answer: strrchr()

Question 3

C headers: in which header are input/output function prototypes and macros defined? Choose the correct standard header for stdio APIs.

Accepted Answer

Introduction / Context: C provides standard I/O via a dedicated header that declares FILE, stream functions, macros, and related constants. This question targets recognition of the correct header file. Given Data / Assumptions: We are referring to the ISO C standard library. Functions include printf, scanf, fopen, fclose, fgetc, fputc, etc. Concept / Approach: The header declares standard input/output facilities: FILE, stdin, stdout, stderr, and functions like printf, scanf, fopen, fgets, and fwrite. Other headers serve different domains (stdlib.h for general utilities, string.h for strings, etc.). Step-by-Step Solution: 1) Identify the category: standard I/O. 2) Recall the canonical header: . 3) Select the matching option. Verification / Alternative check: Any C reference will list as the source of I/O declarations and macros like EOF and BUFSIZ. Why Other Options Are Wrong: conio.h: Non-standard, DOS/Windows compiler specific. stdlib.h: General utilities (memory allocation, conversions, exit), not I/O streams. dos.h: Non-standard DOS utilities. Common Pitfalls: Confusing non-standard headers with ISO C headers. Assuming stdlib.h contains I/O because it is widely used. Final Answer: stdio.h

Question 4

C stdio: can fprintf be used to display output on the screen? If yes, how would you direct output to the console?

Accepted Answer

Introduction / Context: fprintf writes formatted text to a specified stream. This question examines whether the console is just another stream and how to use fprintf for screen output. Given Data / Assumptions: The program is a typical console application. Standard streams stdout and stderr are available. Concept / Approach: Yes. The console is represented by standard output streams. Writing to stdout or stderr sends text to the terminal by default. fprintf(stdout, ...) is equivalent to printf(...); fprintf(stderr, ...) writes error messages that bypass buffering in some environments. Step-by-Step Solution: 1) Include <stdio.h>. 2) Use fprintf(stdout, "Hello\n"); to print to the screen. 3) Optionally, use fprintf(stderr, "Error\n"); for diagnostics. Verification / Alternative check: Replacing printf with fprintf(stdout, ...) produces the same console output under normal conditions. Why Other Options Are Wrong: No: Incorrect because the console is accessible via the standard streams. Common Pitfalls: Forgetting that streams can be redirected: stdout may go to a file or pipe depending on the shell. Assuming only printf can print to the console. Final Answer: Yes

Question 5

C standard streams: what is stderr? Choose the most accurate description used in ISO C.

Accepted Answer

Introduction / Context: C defines three standard text streams: stdin, stdout, and stderr. Understanding their roles is essential for proper error reporting and redirection. Given Data / Assumptions: We are referring to the identifier stderr from . It is implemented as a FILE* object. Concept / Approach: stderr is the standard error stream used for diagnostics and error messages. Unlike stdout, it is often unbuffered or line-buffered to ensure messages appear promptly, even if the program crashes or stdout is redirected. Step-by-Step Solution: 1) Include to access stderr. 2) Write errors with fprintf(stderr, "..."). 3) Benefit from immediate visibility and independent redirection from stdout. Verification / Alternative check: Run a program redirecting only stdout to a file; messages sent to stderr still appear in the terminal, illustrating the separate channel for errors. Why Other Options Are Wrong: standard error types: Not a defined term in C. standard error streams: Plural is misleading; stderr is one stream. standard error definitions: Not the concept being asked. Common Pitfalls: Confusing buffering behavior of stderr vs stdout. Assuming errors must go to stdout. Final Answer: standard error

Question 6

C stdio buffers: what is the purpose of fflush? Choose the best description of how fflush operates on streams.

Accepted Answer

Introduction / Context: fflush ensures that buffered output is physically written to its destination. The exact scope depends on the argument passed to the function per ISO C and common extensions. Given Data / Assumptions: We are dealing with text or binary output streams from <stdio.h>. Some systems support the extension fflush(NULL) to flush all open output streams. Concept / Approach: int fflush(FILE *stream) flushes buffered output for the specified stream when stream is non-NULL. Many implementations also define that fflush(NULL) flushes all open output streams. Input streams are not affected by flushing in standard C (except where system-specific behavior exists). Step-by-Step Solution: 1) If stream != NULL ⇒ write unwritten output bytes to the underlying file or device. 2) If stream == NULL (where supported) ⇒ flush all open output streams. 3) Return 0 on success; EOF on error. Verification / Alternative check: Testing with buffered stdout shows that fflush(stdout) forces immediate display; calling fflush(NULL) (where available) flushes all outputs, useful before abnormal termination. Why Other Options Are Wrong: flushes only specified stream: Incomplete because many systems also support flushing all streams via NULL. flushes input/output buffer and flushes file buffer: Vague and do not capture the argument-based behavior. Common Pitfalls: Assuming input buffers are flushed by fflush—the standard does not require that. Expecting flushing to fix logical errors such as missing newlines. Final Answer: flushes all streams and specified streams.

Question 7

Turbo C (DOS): what does randomize() do? Legacy compiler question about seeding the pseudo-random generator.

Accepted Answer

Introduction / Context: This question refers to Borland/Turbo C for DOS, which provides non-standard functions such as randomize() and random(). Understanding legacy behavior is useful when reading old codebases or porting programs. Given Data / Assumptions: Environment: Turbo C (non-ISO, DOS era). randomize() is available along with random() or rand(). Concept / Approach: In Turbo C, randomize() initializes (seeds) the pseudo-random number generator using a semi-random value, commonly derived from the system clock. It does not return a random number; rather, it prepares subsequent calls to random()/rand() to yield different sequences between runs. Step-by-Step Solution: 1) Call randomize() once near program start. 2) Call random(N) or rand() to obtain pseudo-random values. 3) Observe that sequences differ each run because the seed varies with time. Verification / Alternative check: Without randomize(), consecutive runs produce the same sequence (deterministic seed). With it, the seed changes and so do the outputs. Why Other Options Are Wrong: returns a random number: That describes random() or rand(), not randomize(). returns a random number generator in the specified range: Confuses generation with seeding and range restriction. return a random number with a given seed value: Seed is set, not returned; and randomize() does not take an explicit seed. Common Pitfalls: Assuming Turbo C functions are part of ISO C—portability issues arise. Expecting randomize() to produce a number directly. Final Answer: returns a random number generator with a random value based on time.

Question 8

C conversion utilities: does a function exist to convert int or float to a string (text)? Answer with the standard-library perspective and common practice.

Accepted Answer

Introduction / Context: Converting numbers to text is a routine task. This question asks whether C provides ways to express integers or floating-point values as strings. Given Data / Assumptions: We need a string representation (char array) of an int or float/double. Standard C and widely available extensions can be considered. Concept / Approach: Yes. Standard C offers formatted I/O functions such as sprintf and snprintf to write formatted numbers into a character buffer. Many platforms also provide non-standard helpers such as itoa, ftoa, or gcvt; however, portable code should prefer snprintf with appropriate format specifiers like %d, %ld, %f, %.2f, etc. Step-by-Step Solution: 1) Allocate a buffer: char buf[64]; 2) Use snprintf(buf, sizeof buf, "%d", x); for an int. 3) Use snprintf(buf, sizeof buf, "%f", y); for a float/double. 4) The buffer now contains a NUL-terminated string. Verification / Alternative check: Print the buffer or compare with printf output; both use the same formatting rules. Why Other Options Are Wrong: No: Incorrect; standard formatted output routines exist precisely for this purpose. Common Pitfalls: Using sprintf without bounds checking; prefer snprintf. Relying on non-portable functions like itoa in cross-platform code. Final Answer: Yes

Question 9

What will be the output of the program? #include #include int main() { char dest[] = {97, 97, 0}; char src[] = "aaa"; int i; if((i = memcmp(dest, src, 2))==0) printf("Got it"); else …

Accepted Answer

memcmp compares the first 2 bytes of the blocks dest and src as unsigned chars. So, the ASCII value of 97 is 'a'. if((i = memcmp(dest, src, 2))==0) When comparing the array dest and src as unsigned chars, the first 2 bytes are same in both variables.so memcmp returns '0'. Then, the if(0=0) condition is satisfied. Hence the output is "Got it".

Question 10

What will be the output of the program? #include<stdio.h>  int main() {     int i;     i = scanf("%d %d", &i, &i);     printf("%d ", i);     return 0; }

Accepted Answer

scanf() returns the number of variables to which you are provding the input. i = scanf("%d %d", &i, &i); Here Scanf() returns 2. So i = 2. printf("%d
", i); Here it prints 2.

Question 11

What will be the output of the program? #include #include int main() { float i = 2.5; printf("%f, %d", floor(i), ceil(i)); return 0; }

Accepted Answer

Both ceil() and floor() return the integer found as a double. floor(2.5) returns the largest integral value(round down) that is not greater than 2.5. So output is 2.000000. ceil(2.5) returns 3, while converting the double to int it returns '0'. So, the output is '2.000000, 0'.

Question 12

What will function gcvt() do?

Accepted Answer

The gcvt() function converts a floating-point number to a string. It converts given value to a null-terminated string. #include #include int main(void) { char str[25]; double num; int sig = 5; /* significant digits */ /* a regular number */ num = 9.876; gcvt(num, sig, str); printf("string = %s ", str); /* a negative number */ num = -123.4567; gcvt(num, sig, str); printf("string = %s ", str); /* scientific notation */ num = 0.678e5; gcvt(num, sig, str); printf("string = %s ", str); return(0); } Output: string = 9.876 string = -123.46 string = 67800

Question 13

What will be the output of the program? #include<stdio.h>  int main() {     int i;     i = printf("How r u ");     i = printf("%d ", i);     printf("%d ", i);     return 0; }

Accepted Answer

In the program, printf() returns the number of charecters printed on the console i = printf("How r u
"); This line prints "How r u" with a new line character and returns the length of string printed then assign it to variable i. So i = 8 (length of '
' is 1). i = printf("%d
", i); In the previous step the value of i is 8. So it prints "8" with a new line character and returns the length of string printed then assign it to variable i. So i = 2 (length of '
' is 1). printf("%d
", i); In the previous step the value of i is 2. So it prints "2".

Question 14

What will be the output of the program? #include<stdio.h>  int main() {     int i;     char c;     for(i=1; i<=5; i++)     {         scanf("%c", &c); /* given input is 'b' */         ungetc(c, stdout);         printf("%c", c);         ungetc(c, stdi…

Accepted Answer

The ungetc() function pushes the character c back onto the named input stream, which must be open for reading. This character will be returned on the next call to getc or fread for that stream. One character can be pushed back in all situations. A second call to ungetc without a call to getc will force the previous character to be forgotten.

Question 15

What will be the output of the program? #include<stdio.h>  int main() {     int i;     char c;     for(i=1; i<=5; i++)     {         scanf("%c", &c); /* given input is 'a' */         printf("%c", c);         ungetc(c, stdin);     }     r…

Accepted Answer

for(i=1; i<=5; i++) Here the for loop runs 5 times. Loop 1: scanf("%c", &c); Here we give 'a' as input. printf("%c", c); prints the character 'a' which is given in the previous "scanf()" statement. ungetc(c, stdin); "ungetc()" function pushes character 'a' back into input stream. Loop 2: Here the scanf("%c", &c); get the input from "stdin" because of "ungetc" function. printf("%c", c); Now variable c = 'a'. So it prints the character 'a'. ungetc(c, stdin); "ungetc()" function pushes character 'a' back into input stream. This above process will be repeated in Loop 3, Loop 4, Loop 5.

Question 16

What will be the output of the program? #include #include int main() { char *i = "55.555"; int result1 = 10; float result2 = 11.111; result1 = result1+atoi(i); result2 = result2+atof(i); printf("…

Accepted Answer

Function atoi() converts the string to integer. Function atof() converts the string to float. result1 = result1+atoi(i); Here result1 = 10 + atoi(55.555); result1 = 10 + 55; result1 = 65; result2 = result2+atof(i); Here result2 = 11.111 + atof(55.555); result2 = 11.111 + 55.555000; result2 = 66.666000; So the output is "65, 66.666000" .

Library Functions Questions