Strings Questions and Answers

Q: #include <stdio.h> void my_toUpper(char* str, int index) { *(str + index) &= ~32; } int main() { char* arr = "geeksquiz"; my_toUpper(arr, 0); my_toUpper(arr, 5); printf("%s", arr); return 0; }

Correct answer: Compiler dependentarr points to a string literal, and modifying one is undefined behaviour. Most compilers place literals in read-only memory, so the write faults at run time; others allow it, and the program prints GeeksQuiz. The fix is char arr[] = "geeksquiz";, which gives a modifiable copy. (The &= ~32 trick works because upper and lower case differ by exactly bit 5.)

Q: In below program, what would you put in place of “?” to print “Quiz”? #include <stdio.h> int main() { char arr[] = "GeeksQuiz"; printf("%s", ?); return 0; }

Correct answer: (arr+5)"GeeksQuiz" has Q at index 5, counting from 0, so arr+5 points at the start of Quiz and %s prints from there to the terminating null. arr+4 would give sQuiz.

Q: Which of the following functions returns a pointer to the located string or a null pointer if string is not found.

Correct answer: strstr()strstr(haystack, needle) searches for the first occurrence of one string inside another and returns a pointer to where it begins, or NULL if it is not there. strchr finds a single character rather than a string.

Q: What will be the output of the program ? #include <stdio.h> int main() { printf(5+"Good Morning\n"); return 0; }

Correct answer: MorningA string literal in an expression yields a pointer to its first character, so 5+"Good Morning\n" is a pointer five characters further along. Counting G-o-o-d-space, index 5 is the M, and printf prints from there: Morning.

Q: What will be the output of the program ? #include <stdio.h> #include <string.h> int main() { char str1[20] = "Hello", str2[20] = " World"; printf("%s\n", strcpy(str2, strcat(str1, str2))); return 0; }

Correct answer: Hello WorldWork outwards. strcat(str1, str2) appends " World" to "Hello", making str1 hold "Hello World" and returning a pointer to it. strcpy(str2, ...) then copies that into str2 and returns str2. Both arrays are 20 bytes, so there is room, and the printed string is Hello World.

Q: The library function used to find the last occurrence of a character in a string is

Correct answer: strrchr()strrchr() searches from the end and returns a pointer to the last occurrence of the character, or NULL. It is the standard way of finding a file extension or the last directory separator in a path.

Q: If the size of pointer is 32 bits What will be the output of the program ? #include <stdio.h> int main() { char a[] = "Visual C++"; char *b = "Visual C++"; printf("%d, %d\n", sizeof(a), sizeof(b)); printf("%d, %d", sizeof(*a), sizeof(*b)); return 0; }

Correct answer: 11, 4 1, 1a is an array, so sizeof(a) is the whole thing: 10 characters plus the terminating null, 11. b is a pointer, so sizeof(b) is 32 bits, 4 bytes. Both *a and *b are single chars, so each is 1.

Q: What will the given C code do? int memcmp(const void *str1, const void *str2, size_t n)

Correct answer: compares the first n bytes of str1 and str2memcmp compares the first n bytes of the two objects, returning a negative, zero or positive value like strcmp. It copies nothing, and unlike the str functions it takes no notice of null bytes - it compares exactly n bytes whatever they contain.

21.

#include <stdio.h> 
   
void my_toUpper(char* str, int index) 
{ 
    *(str + index) &= ~32; 
} 
   
int main() 
{ 
    char* arr = "geeksquiz"; 
    my_toUpper(arr, 0); 
    my_toUpper(arr, 5); 
    printf("%s", arr); 
    return 0; 
}

A.GeeksQuiz
B.geeksquiz
C.Compiler dependent

Answer: C

Correct answer: Compiler dependent

arr points to a string literal, and modifying one is undefined behaviour. Most compilers place literals in read-only memory, so the write faults at run time; others allow it, and the program prints GeeksQuiz. The fix is char arr[] = "geeksquiz";, which gives a modifiable copy. (The &= ~32 trick works because upper and lower case differ by exactly bit 5.)

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22.

In below program, what would you put in place of “?” to print “Quiz”?

#include <stdio.h> 
int main()  
{  
  char arr[] = "GeeksQuiz";  
  printf("%s", ?);  
  return 0;  
}

A.arr
B.(arr+5)
C.(arr+4)
D.Not possible

Answer: B

Correct answer: (arr+5)

"GeeksQuiz" has Q at index 5, counting from 0, so arr+5 points at the start of Quiz and %s prints from there to the terminating null. arr+4 would give sQuiz.

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23.

Which of the following functions returns a pointer to the located string or a null pointer if string is not found.

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

Answer: B

Correct answer: strstr()

strstr(haystack, needle) searches for the first occurrence of one string inside another and returns a pointer to where it begins, or NULL if it is not there. strchr finds a single character rather than a string.

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24.

What will be the output of the program ?

#include <stdio.h>

int main()
{
    printf(5+"Good Morning\n");
    return 0;
}

A.Good Morning
B.Good
C.M
D.Morning

Answer: D

Correct answer: Morning

A string literal in an expression yields a pointer to its first character, so 5+"Good Morning\n" is a pointer five characters further along. Counting G-o-o-d-space, index 5 is the M, and printf prints from there: Morning.

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25.

What will be the output of the program ?

#include <stdio.h>
#include <string.h>

int main()
{
    char str1[20] = "Hello", str2[20] = " World";
    printf("%s\n", strcpy(str2, strcat(str1, str2)));
    return 0;
}

A.Hello
B.World
C.Hello World
D.WorldHello

Answer: C

Correct answer: Hello World

Work outwards. strcat(str1, str2) appends " World" to "Hello", making str1 hold "Hello World" and returning a pointer to it. strcpy(str2, ...) then copies that into str2 and returns str2. Both arrays are 20 bytes, so there is room, and the printed string is Hello World.

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26.

Which of the following is the right syntax to copy n characters from the object pointed to by s2 into the object pointed to by s1?

A.void *memcpy(void *s1,const void *s2,size_t n);
B.void *memcpy(void *s2, const void *s1, size_t n);
C.void memcpy(void *s1,const void *s2, size_t n);
D.void memcpy(void *s2,const void *s1,size_t n);

Answer: A

Correct answer: void *memcpy(void *s1,const void *s2,size_t n);

The destination comes first, as it does throughout the library - the same order as an assignment. The source is const, since it is only read, and the function returns void *, the destination pointer, so calls can be chained. The two regions must not overlap; memmove is the version that copes if they do.

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27.

The library function used to find the last occurrence of a character in a string is

A.strnstr()
B.laststr()
C.strrchr()
D.strstr()

Answer: C

Correct answer: strrchr()

strrchr() searches from the end and returns a pointer to the last occurrence of the character, or NULL. It is the standard way of finding a file extension or the last directory separator in a path.

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28.

What is the use of function char *strchr(ch, c)?

A.return pointer to first occurrence of ch in c or NULL if not present
B.return pointer to first occurrence of c in ch or NULL if not present
C.return pointer to first occurrence of ch in c or ignores if not present
D.return pointer to first occurrence of cin ch or ignores if not present

Answer: B

Correct answer: return pointer to first occurrence of c in ch or NULL if not present

strchr(ch, c) searches the string ch for the character c and returns a pointer to the first occurrence, or NULL if there is none. Returning a pointer rather than an index is what lets the result be used directly as the start of a substring. The terminating null counts as part of the string, so searching for '\0' finds the end.

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29.

If the size of pointer is 32 bits What will be the output of the program ?

#include <stdio.h>

int main()
{
    char a[] = "Visual C++";
    char *b = "Visual C++";
    printf("%d, %d\n", sizeof(a), sizeof(b));
    printf("%d, %d", sizeof(*a), sizeof(*b));
    return 0;
}

A.10, 22, 2
B.10, 41, 2
C.11, 41, 1
D.12, 22, 2

Answer: C

Correct answer: 11, 4 1, 1

a is an array, so sizeof(a) is the whole thing: 10 characters plus the terminating null, 11. b is a pointer, so sizeof(b) is 32 bits, 4 bytes. Both *a and *b are single chars, so each is 1.

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30.

What will the given C code do?

int memcmp(const void *str1, const void *str2, size_t n)

A.compares the first n bytes of str1 and str2
B.copies the first n bytes of str1 to str2
C.copies the first n bytes of str2 to str1
D.invalid function

Answer: A

Correct answer: compares the first n bytes of str1 and str2

memcmp compares the first n bytes of the two objects, returning a negative, zero or positive value like strcmp. It copies nothing, and unlike the str functions it takes no notice of null bytes - it compares exactly n bytes whatever they contain.

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