Strings Questions and Answers

Q: What will the following C code do? void *memset(void *s, int c, size_t n) { unsigned char ch = c; unsigned char *su; for (su = s; 0 < n; ++su, --n) *su = ch; return (s); }

Correct answer: store c throughout unsigned char s[n]This is the textbook implementation of memset. The byte value c is copied into an unsigned char, and the loop walks n bytes from s, writing that value into each. Using unsigned char matters: it is the type guaranteed to address every byte of an object without sign issues.

Q: The function strspn() is the complement of strcspn().

Correct answer: trueThe two are complementary. strspn(s, set) counts the initial run of characters that are in the set; strcspn(s, set) counts the initial run of those that are not. Used together they let a string be walked field by field - skip the delimiters, then take the token.

Q: What will be the value of var for the following C statement? var = strcmp("Hello", "World");

Correct answer: -1strcmp compares character by character, and the first pair decides it: 'H' is 72 while 'W' is 87, so the first string sorts before the second and the result is negative. The standard promises only the sign, not the magnitude - some libraries return the difference, here -15 - so code should test < 0 rather than == -1.

101.

What will the following C code do?

void *memset(void *s, int c, size_t n)
{
    unsigned char ch = c;
    unsigned char *su;
    for (su = s; 0 < n; ++su, --n)
        *su = ch;
    return (s);
}

A.store c throughout unsigned char s[n]
B.store c throughout signed char s[n]
C.find first occurrence of c in s[n]
D.find last occurrence of c in s[n]

Answer: A

Correct answer: store c throughout unsigned char s[n]

This is the textbook implementation of memset. The byte value c is copied into an unsigned char, and the loop walks n bytes from s, writing that value into each. Using unsigned char matters: it is the type guaranteed to address every byte of an object without sign issues.

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102.

The function strspn() is the complement of strcspn().

A.true
B.false

Answer: A

Correct answer: true

The two are complementary. strspn(s, set) counts the initial run of characters that are in the set; strcspn(s, set) counts the initial run of those that are not. Used together they let a string be walked field by field - skip the delimiters, then take the token.

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103.

What will be the value of var for the following C statement?

var = strcmp("Hello", "World");

A.-1
B.1
C.strcmp has void return-type

Answer: A

Correct answer: -1

strcmp compares character by character, and the first pair decides it: 'H' is 72 while 'W' is 87, so the first string sorts before the second and the result is negative. The standard promises only the sign, not the magnitude - some libraries return the difference, here -15 - so code should test < 0 rather than == -1.

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Strings Questions and Answers

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