Strings Questions and Answers

Q: Predict the output of the following program: #include <stdio.h> int main() { char str[] = "%d %c", arr[] = "GeeksQuiz"; printf(str, 0[arr], 2[arr + 3]); return 0; }

Correct answer: 71 QBoth subscripts are written backwards, which is legal: 0[arr] is arr[0] = 'G', and 2[arr+3] is *(arr+3+2) = arr[5] = 'Q'. The format string, itself held in an array, prints the first with %d - giving the character code 71 - and the second with %c, giving Q.

Q: What will be the output of the following C code? const char str1[]="ABCDEF1234567"; const char str2[] = "269"; len = strcspn(str1, str2); printf("First matching character is at %d\n", len + 1);

Correct answer: First matching character is at 8strcspn returns the length of the initial segment of str1 containing no character from str2. Scanning ABCDEF1234567 against 269, the first seven characters ABCDEF1 are all absent from the set, and the eighth, 2, is present. So the function returns 7, and the program prints 7 + 1 = 8 - the 1-based position of the first match.

Q: Which of the given function is used to return a pointer to the located character?

Correct answer: strchr()strchr() returns a pointer to the located character - the first occurrence of it in the string - or NULL. strrchr finds the last occurrence, memchr searches a fixed-length block rather than a string, and strxfrm transforms rather than searches.

Q: String operation such as strcat(s, t), strcmp(s, t), strcpy(s, t) and strlen(s) rely heavily upon

Correct answer: Presence of NULL characterEvery one of them finds the end of a string by looking for the terminating null - there is no stored length. A string that has lost its null makes all of them read past the end of the array, which is the single commonest cause of memory corruption in C.

Q: How will you print \n on the screen?

Correct answer: printf("\\n");Inside a string literal a backslash starts an escape sequence, so a literal backslash must itself be escaped: "\\n" is the two characters backslash and n. "\n" would be the single newline character, and single quotes make a character constant rather than a string.

Q: If the two strings are identical, then strcmp() function returns

Correct answer: 0strcmp returns 0 when the strings are identical, a negative value when the first sorts before the second, and a positive one when it sorts after. Returning 0 for a match is what makes if (strcmp(a, b)) such a common mistake - it is true when the strings differ.

Q: The______function returns a pointer to the first character of a token.

Correct answer: strtok()strtok() returns a pointer to the first character of the next token, or NULL when there are none left. It finds a token by skipping leading delimiters and then writing a null over the delimiter that ends it.

Q: Does strcat() add a terminating null character?

Correct answer: Alwaysstrcat always writes a terminating null after the characters it appends - the result is a proper C string. That is why the destination must have room for the two strings and one more byte, and why the function cannot check whether that room exists.

Q: Which of the following function compares 2 strings with case-insensitively?

Correct answer: strcasecmp(s, t)strcasecmp compares two strings ignoring the difference between upper and lower case. It is a POSIX function rather than a standard C one - the Microsoft spelling is _stricmp - but it is available almost everywhere. strcmp compares by character code, so "abc" and "ABC" come out unequal.

31.

Predict the output of the following program:

#include <stdio.h> 
int main() 
{ 
    char str[] = "%d %c", arr[] = "GeeksQuiz"; 
    printf(str, 0[arr], 2[arr + 3]); 
    return 0; 
}

A.G Q
B.71 81
C.71 Q
D.Compile-time error

Answer: C

Correct answer: 71 Q

Both subscripts are written backwards, which is legal: 0[arr] is arr[0] = 'G', and 2[arr+3] is *(arr+3+2) = arr[5] = 'Q'. The format string, itself held in an array, prints the first with %d - giving the character code 71 - and the second with %c, giving Q.

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32.

There are two groups of string functions defined in the header <string.h>. What are they?

A.first group names beginning with str; second group names beginning with mem
B.first group names beginning with str; second group names beginning with is
C.first group names beginning with string; second group names beginning with mem
D.first group names beginning with str; second group names beginning with type

Answer: A

Correct answer: first group names beginning with str; second group names beginning with mem

<string.h> holds two families. The str functions work on null-terminated strings, stopping at the terminator. The mem functions work on objects of a given length, taking a byte count and paying no attention to nulls - which is why they can copy or compare arbitrary binary data.

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33.

What will be the output of the following C code?

const char str1[]="ABCDEF1234567";
const char str2[] = "269";
len = strcspn(str1, str2);
printf("First matching character is at %d\n", len + 1);

A.First matching character is at 8
B.First matching character is at 7
C.First matching character is at 9
D.First matching character is at 12

Answer: A

Correct answer: First matching character is at 8

strcspn returns the length of the initial segment of str1 containing no character from str2. Scanning ABCDEF1234567 against 269, the first seven characters ABCDEF1 are all absent from the set, and the eighth, 2, is present. So the function returns 7, and the program prints 7 + 1 = 8 - the 1-based position of the first match.

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34.

Which of the given function is used to return a pointer to the located character?

A.strrchr()
B.strxfrm()
C.memchr()
D.strchr()

Answer: D

Correct answer: strchr()

strchr() returns a pointer to the located character - the first occurrence of it in the string - or NULL. strrchr finds the last occurrence, memchr searches a fixed-length block rather than a string, and strxfrm transforms rather than searches.

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35.

String operation such as strcat(s, t), strcmp(s, t), strcpy(s, t) and strlen(s) rely heavily upon

A.Presence of NULL character
B.Presence of new-line character
C.Presence of any escape sequence
D.None of the mentioned

Answer: A

Correct answer: Presence of NULL character

Every one of them finds the end of a string by looking for the terminating null - there is no stored length. A string that has lost its null makes all of them read past the end of the array, which is the single commonest cause of memory corruption in C.

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36.

How will you print \n on the screen?

A.printf("\n");
B.echo "\\n";
C.printf('\n');
D.printf("\\n");

Answer: D

Correct answer: printf("\\n");

Inside a string literal a backslash starts an escape sequence, so a literal backslash must itself be escaped: "\\n" is the two characters backslash and n. "\n" would be the single newline character, and single quotes make a character constant rather than a string.

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37.

If the two strings are identical, then strcmp() function returns

A.-1
B.1
C.Yes
D.0

Answer: D

Correct answer: 0

strcmp returns 0 when the strings are identical, a negative value when the first sorts before the second, and a positive one when it sorts after. Returning 0 for a match is what makes if (strcmp(a, b)) such a common mistake - it is true when the strings differ.

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38.

The______function returns a pointer to the first character of a token.

A.strstr()
B.strcpy()
C.strspn()
D.strtok()

Answer: D

Correct answer: strtok()

strtok() returns a pointer to the first character of the next token, or NULL when there are none left. It finds a token by skipping leading delimiters and then writing a null over the delimiter that ends it.

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39.

Does strcat() add a terminating null character?

A.Only if there is space
B.Always
C.Depends on the standard
D.Depends on the compiler

Answer: B

Correct answer: Always

strcat always writes a terminating null after the characters it appends - the result is a proper C string. That is why the destination must have room for the two strings and one more byte, and why the function cannot check whether that room exists.

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40.

Which of the following function compares 2 strings with case-insensitively?

A.strcmp(s, t)
B.strcmpcase(s, t)
C.strcasecmp(s, t)
D.strchr(s, t)

Answer: C

Correct answer: strcasecmp(s, t)

strcasecmp compares two strings ignoring the difference between upper and lower case. It is a POSIX function rather than a standard C one - the Microsoft spelling is _stricmp - but it is available almost everywhere. strcmp compares by character code, so "abc" and "ABC" come out unequal.

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