Strings Questions and Answers

Answer: C

The correct option is S1 has a lexical error and S3 has a semantic error.

In S1 the string literal "Hello; is never closed before the end of the line. The lexical analyser cannot form a valid string token, so this is a lexical error.

S2 is valid: the semicolon inside the quotes is part of the string, and the statement ends with its own semicolon.

S3 is well formed syntactically, but it initialises an int * with a string literal, whose type is a char array that decays to char *. That type mismatch is detected during semantic analysis, so it is a semantic error.

Calling S1's error syntactic, or saying S2 has any error, misplaces the phase that catches each fault.

Answer: D

The program prints Hello World!d!.

The array holds "@#Hello World!": 14 characters in a[0] to a[13], then the terminator in a[14]. The call stringcopy(a, a + 2) copies from the third character onwards into the start of the array.

The loop while(*t) *s++ = *t++; stops when *t is the terminator, without copying it. So it copies the 12 characters 'Hello World!' into a[0] to a[11], and a[12] and a[13] keep their old values, 'd' and '!'. The original terminator at a[14] is untouched.

printf then prints a[0] to a[13]: Hello World!d!. 'Hello World!' alone would be printed only if the terminator were copied too. The original string and 'ello World!' would need different copy offsets.

Answer: A

This function returns a pointer to the first occurrence in s1 of any of the entire sequence of characters specified in s2, or a null pointer if the sequence is not present in s1.
char *strstr(const char *s1, const char *s2)

Answer: A

Correct answer: memcpy()

memcpy() copies a given number of bytes from one object to another. The others do not exist: the string copy is strcpy(), not strcopy(), and there is no memcopy() or strxcpy().

Answer: C

Correct answer: strncat()

strncat() appends at most n characters from the source, and always adds a terminating null - so the destination needs n+1 bytes free. The bounded form exists to keep an append from running past the end of the buffer.

Answer: C

Correct answer: strstr()

strstr(haystack, needle) finds the first occurrence of one string inside another and returns a pointer to where it starts. strchr and strrchr search for a single character, not a substring.

Answer: B

Correct answer: unequal

This is the trap in strcmp: it returns 0 when the strings are equal, and 0 is false. The two strings here have the same contents, so the condition fails and the else branch runs, printing unequal. The test should be written if (strcmp(a, b) == 0).

Answer: B

Correct answer: k, k

mess[2] is "Don't walk behind me...", and index 9 counts D-o-n-'-t-space-w-a-l-k - giving k. The second expression, *(*(mess+2)+9), is the same thing written in pointer form, since mess[i] is *(mess+i). So both print k.

Answer: C

Correct answer: gets()

gets() reads characters up to the newline, so it takes a whole line including the spaces between words. scanf("%s", ...) stops at the first whitespace and would read only the first word. printf and puts write rather than read. Note that gets() cannot limit the input length and has been removed from modern C for that reason; fgets() is what should be used in real code.

Answer: B

Correct answer: strrchr(s, c);

The extra r is for reverse: strrchr returns a pointer to the last occurrence of the character. strchr gives the first; the other two names do not exist.