Library Functions Questions and Answers

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

Correct answer: 2scanf returns the number of items successfully converted and assigned, not the values themselves. Two conversions succeed here, so it returns 2, and that is what is stored in i and printed - overwriting whatever the two conversions had put there.

Q: scanf() or atoi() function can be used to convert a string like "436" in to integer.

Correct answer: YesBoth work. atoi("436") converts the string directly, and sscanf(str, "%d", &n) does the same with error reporting. strtol is better than either, since it distinguishes a genuine 0 from a failed conversion.

Q: A non-zero value is returned, if setjmp() returns from a longjmp() function call.

Correct answer: truesetjmp returns 0 when it is called directly to save the environment, and a non-zero value when control arrives there from a longjmp - the value longjmp was given. Testing the return value is how the code distinguishes the two arrivals.

Q: Point out the error in the following program. #include <stdio.h> int main() { char str[] = "IndiaBIX"; printf("%.#s %2s", str, str); return 0; }

Correct answer: No errorThere is no error. %.#s and %2s are not the specifiers the author probably intended, but printf is not obliged to reject them - the format string is parsed at run time, and undefined or unrecognised conversions do not stop the program compiling. The array declaration is perfectly ordinary.

Q: Which function will return the quotient and remainder on division of numerator with denominator?

Correct answer: div()div(num, den) returns a div_t structure containing both the quotient (.quot) and the remainder (.rem). Getting both from one call is cheaper than a separate / and %, and the truncation behaviour is guaranteed. div_t is the type, not a function.

Q: Which function returns the number of bytes in the multibyte character pointed to by its argument?

Correct answer: mblen()mblen() returns the number of bytes in the multibyte character its argument points to. getenv reads environment variables, and bsearch and qsort search and sort arrays.

Q: Does there any function exist to convert the int or float to a string?

Correct answer: YesYes - sprintf does it portably: sprintf(buf, "%d", n). The old libraries also provided itoa, ltoa and gcvt, and C11 added snprintf, which is safer because it takes the buffer size.

Q: What does the raise() function declared in signal.h do?

Correct answer: reports a synchronous signalraise(sig) sends a signal to the running program itself, so it arrives synchronously at a known point in the code. Installing a handler is the job of signal(); asynchronous signals come from outside the program.

Q: Select the macro that affects the information provided by localeconv function.

Correct answer: LC_NUMERIClocaleconv() reports the numeric and monetary conventions, so it is governed by LC_NUMERIC - decimal point and thousands separator - and by LC_MONETARY for the currency fields. LC_COLLATE affects string comparison and LC_CTYPE character classification; neither shows up in the struct lconv.

Q: Which standard library function will you use to find the last occurrence of a character in a string in C?

Correct answer: strrchr()strrchr() - the extra r is for reverse - returns a pointer to the last occurrence of a character in a string, or NULL if it is absent. It is the usual way to find a file extension or the last separator in a path. The other three names do not exist; strchr() finds the first occurrence.

81.

What will be the output of the program?

#include <stdio.h>

int main()
{
    int i;
    i = scanf("%d %d", &i, &i);
    printf("%d\n", i);
    return 0;
}

A.1
B.2
C.Garbage value
D.Error: cannot assign scanf to variable

Answer: B

Correct answer: 2

scanf returns the number of items successfully converted and assigned, not the values themselves. Two conversions succeed here, so it returns 2, and that is what is stored in i and printed - overwriting whatever the two conversions had put there.

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82.

scanf() or atoi() function can be used to convert a string like "436" in to integer.

A.Yes
B.No

Answer: A

Correct answer: Yes

Both work. atoi("436") converts the string directly, and sscanf(str, "%d", &n) does the same with error reporting. strtol is better than either, since it distinguishes a genuine 0 from a failed conversion.

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83.

A non-zero value is returned, if setjmp() returns from a longjmp() function call.

A.false
B.true

Answer: B

Correct answer: true

setjmp returns 0 when it is called directly to save the environment, and a non-zero value when control arrives there from a longjmp - the value longjmp was given. Testing the return value is how the code distinguishes the two arrivals.

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84.

Point out the error in the following program.

#include <stdio.h>

int main()
{
    char str[] = "IndiaBIX";
    printf("%.#s %2s", str, str);
    return 0;
}

A.Error: in Array declaration
B.Error: printf statement
C.Error: unspecified character in printf
D.No error

Answer: D

Correct answer: No error

There is no error. %.#s and %2s are not the specifiers the author probably intended, but printf is not obliged to reject them - the format string is parsed at run time, and undefined or unrecognised conversions do not stop the program compiling. The array declaration is perfectly ordinary.

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85.

Which function will return the quotient and remainder on division of numerator with denominator?

A.div()
B.div_t()
C.ldiv_t()
D.labs()

Answer: A

Correct answer: div()

div(num, den) returns a div_t structure containing both the quotient (.quot) and the remainder (.rem). Getting both from one call is cheaper than a separate / and %, and the truncation behaviour is guaranteed. div_t is the type, not a function.

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86.

Which function returns the number of bytes in the multibyte character pointed to by its argument?

A.getenv()
B.bsearch()
C.mblen()
D.qsort()

Answer: C

Correct answer: mblen()

mblen() returns the number of bytes in the multibyte character its argument points to. getenv reads environment variables, and bsearch and qsort search and sort arrays.

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87.

Does there any function exist to convert the int or float to a string?

A.Yes
B.No

Answer: A

Correct answer: Yes

Yes - sprintf does it portably: sprintf(buf, "%d", n). The old libraries also provided itoa, ltoa and gcvt, and C11 added snprintf, which is safer because it takes the buffer size.

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88.

What does the raise() function declared in signal.h do?

A.reports a synchronous signal
B.let's you specify handling of signals
C.reports a asynchronous signal
D.doesn't let you specify handling of signals

Answer: A

Correct answer: reports a synchronous signal

raise(sig) sends a signal to the running program itself, so it arrives synchronously at a known point in the code. Installing a handler is the job of signal(); asynchronous signals come from outside the program.

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89.

Select the macro that affects the information provided by localeconv function.

A.LC_ALL
B.LC_COLLATE
C.LC_NUMERIC
D.LC_CTYPE

Answer: C

Correct answer: LC_NUMERIC

localeconv() reports the numeric and monetary conventions, so it is governed by LC_NUMERIC - decimal point and thousands separator - and by LC_MONETARY for the currency fields. LC_COLLATE affects string comparison and LC_CTYPE character classification; neither shows up in the struct lconv.

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90.

Which standard library function will you use to find the last occurrence of a character in a string in C?

A.strnchar()
B.strchar()
C.strrchar()
D.strrchr()

Answer: D

Correct answer: strrchr()

strrchr() - the extra r is for reverse - returns a pointer to the last occurrence of a character in a string, or NULL if it is absent. It is the usual way to find a file extension or the last separator in a path. The other three names do not exist; strchr() finds the first occurrence.

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