geektest - Input and Output

Input and Output

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; }

	9
	1
C	10
D	100

Question 1 Explanation: 

scanf returns the no. of inputs it has successfully read. Seehttp://geeksforgeeks.org/archives/674

Question 3 WRONG

#include <stdio.h>   int main() {   printf(" \"GEEKS %% FOR %% GEEKS\"");   getchar();   return 0; }

	“GEEKS % FOR % GEEKS”
B	GEEKS % FOR % GEEKS
	\"GEEKS %% FOR %% GEEKS\"
D	GEEKS %% FOR %% GEEKS

Predict the output of the below program:

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

A	Compile-time error
B	Runtime error
	Q
D	s

Discuss it

Question 5 Explanation: 

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 WRONG

Predict the output of below program:

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

A	Compile-time error
B	Runtime error
	Q
	s

Discuss it

Question 6 Explanation: 

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 8 WRONG

Which of the following is true

	gets() doesn't do any array bound testing and should not be used.
	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

Discuss it

Question 8 Explanation: 

See gets() is risky to use!

Question 9 CORRECT

What does the following C statement mean?

scanf("%4s", str);

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

Discuss it

Question 9 Explanation: 

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;
}

Question 10 WRONG

#include<stdio.h>   int main() {     char *s = "Geeks Quiz";     int n = 7;     printf("%.*s", n, s);     return 0; }

A	Geeks Quiz
B	Nothing is printed
	Geeks Q
	Geeks Qu

Discuss it

Question 10 Explanation: 

.* means The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.

#include<stdio.h> int main() {     printf("%d", printf("%d", 1234));     return 0; }

	12344
	12341
C	11234
D	41234

Discuss it

Question 12 Explanation: 

printf() returns the number of characters successfully printed on the screen.

Question 14 CORRECT

Normally user programs are prevented from handling I/O directly by I/O instructions in them. For CPUs having explicit I/O instructions, such I/O protection is ensured by having the I/O instructions privileged. In a CPU with memory mapped I/O, there is no explicit I/O instruction. Which one of the following is true for a CPU with memory mapped I/O?

	I/O protection is ensured by operating system routine (s)
B	I/O protection is ensured by a hardware trap
C	I/O protection is ensured during system configuration
D	I/O protection is not possible

Discuss it

Question 14 Explanation: 

User applications are not allowed to perform I/O in user mode - All I/O requests are handled through system calls that must be performed in kernel mode.

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