C Input and Output

Question 1

Predict the output of following program?

#include "stdio.h"
int main()
{
    char arr[100];
    printf("%d", scanf("%s", arr));
    /* Suppose that input value given
        for above scanf is "GeeksQuiz" */
    return 1;
}

• A. 9
• B. 1
• C. 10
• D. 100

Answer: (B)

C Input and Output
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In C, scanf returns the no. of inputs it has successfully read. See http://geeksforgeeks.org/archives/674

Question 2

Predict output of the following program 

C

#include <stdio.h>
int main()
{
   printf("new_c_questionbr");
   printf("geeksforgeeks"); 
   getchar();
   return 0;
}

• A. ew_c_question
  geeksforgeeks
  
• B. new_c_ques
  geeksforgeeks
  
• C.
  geeksforgeeks
  
• D. Depends on terminal configuration

Answer: (D)

C Input and Output C++ Constructors
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See https://stackoverflow.com/questions/17236242/usage-of-b-and-r-in-c/%22

Question 3

#include <stdio.h>

int main() 
{ 
  printf(" "GEEKS %% FOR %% GEEKS""); 
  getchar(); 
  return 0; 
}

• A. “GEEKS % FOR % GEEKS”
• B. GEEKS % FOR % GEEKS
• C. \"GEEKS %% FOR %% GEEKS\"
• D. GEEKS %% FOR %% GEEKS

Answer: (A)

C Input and Output
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Backslash (\\\\) works as escape character for double quote (“). For explanation of %%, see http://www.geeksforgeeks.org/how-to-print-using-printf/

Question 4

C

#include <stdio.h>
// Assume base address of "GeeksQuiz" to be 1000
int main()
{
   printf(5 + "GeeksQuiz");
   return 0;
}

• A. GeeksQuiz
  
• B. Quiz
  
• C. 1005
  
• D. Compile-time error
  

Answer: (B)

C Input and Output 50 C Language MCQs with Answers
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printf is a library function defined under stdio.h header file. The compiler adds 5 to the base address of the string through the expression 5 + "GeeksQuiz" . Then the string "Quiz" gets passed to the standard library function as an argument.

Question 5

Predict the output of the below program:

C

#include <stdio.h>

int main()
{
    printf("%c ", 5["GeeksQuiz"]);
    return 0;
}

• A. Compile-time error
• B. Runtime error
• C. Q
• D. s

Answer: (C)

C Input and Output
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The crux of the program lies in the expression: 5["GeeksQuiz"] This expression is broken down by the compiler as: *(5 + "GeeksQuiz"). Adding 5 to the base address of the string increments the pointer(lets say a pointer was pointing to the start(G) of the string initially) to point to Q. Applying value-of operator gives the character at the location pointed to by the pointer i.e. Q.

Question 6

Predict the output of below program:

#include <stdio.h>
int main()
{
    printf("%c ", "GeeksQuiz"[5]);
    return 0;
}

• A. Compile-time error
• B. Runtime error
• C. Q
• D. s

Answer: (C)

C Input and Output
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The crux of the program lies in the expression: "GeeksQuiz"[5]. This expression is broken down by the compiler as: *(“GeeksQuiz” + 5). Adding 5 to the base address of the string increments the pointer(lets say a pointer was pointing to the start(G) of the string initially) to point to Q. Applying value-of operator gives the character at the location pointed to by the pointer i.e. Q.

Question 7

When a copy constructor may be called?

• A. When an object of the class is returned by value.
• B. When an object of the class is passed (to a function) by value as an argument.
• C. When an object is constructed based on another object of the same class
• D. When compiler generates a temporary object.
• E. All of the above

Answer: (E)

C++ Constructors C Input and Output
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See When is copy constructor called?

Question 8

Which of the following is true

• A. gets() can read a string with newline characters but a normal scanf() with %s can not.
• B. gets() can read a string with spaces but a normal scanf() with %s can not.
• C. gets() can always replace scanf() without any additional code.
• D. None of the above

Answer: (B)

C Input and Output
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gets() can read a string with spaces but a normal scanf() with %s can not. Consider following program as an example. If we enter "Geeks Quiz" as input in below program, the program prints "Geeks" But in the following program, if we enter "Geeks Quiz", it prints "Geeks Quiz"

Question 9

Which of the following is true

• A. gets() doesn't do any array bound testing and should not be used. 
  
• B. fgets() should be used in place of gets() only for files, otherwise gets() is fine
  
• C. gets() cannot read strings with spaces
  
• D. None of the above
  

Answer: (A)

C Input and Output 50 C Language MCQs with Answers
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Use of gets() generates the risk of an overflow of the allocated buffer. This happens because the function gets(), doesn't know the size of the buffer, and continues reading until it finds a newline "\n" or encounters EOF, and so it may overflow the bounds of the buffer it was given. 

See gets() is risky to use!

Question 10

What does the following C statement mean? 

C

 scanf("%4s", str);

• A. Read exactly 4 characters from console.
  
• B. Read maximum 4 characters from console.
  
• C. Read a string str in multiples of 4
  
• D. Nothing
  

Answer: (B)

C Input and Output 50 C Language MCQs with Answers
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Try following program, enter GeeksQuiz, the output would be "Geek" 

#include <stdio.h>

int main()
{
    char str[50] = {0};
    scanf("%4s", str);
    printf(str);
    getchar();
    return 0;
}