Input / Output - · PDF fileInput / Output General Questions 1 ... FILE *stream); fgets reads characters from stream into the string s ... The while loop runs three times and it write

Saikat Banerjee

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Input / Output General Questions

1. In a file contains the line "I am a boy\r\n" then on reading this line into the array str using fgets(). What

will str contain?

A. "I am a boy\r\n\0" B. "I am a boy\r\0"

C. "I am a boy\n\0" D. "I am a boy"

Answer & Explanation

Answer: Option C

Explanation:

Declaration: char *fgets(char *s, int n, FILE *stream);

fgets reads characters from stream into the string s. It stops when it reads either n - 1 characters or a

newline character, whichever comes first.

Therefore, the string str contain "I am a boy\n\0"

2. What is the purpose of "rb" in fopen() function used below in the code?

FILE *fp;

fp = fopen("source.txt", "rb");

A. open "source.txt" in binary mode for reading

B. open "source.txt" in binary mode for reading and writing

C. Create a new file "source.txt" for reading and writing

D. None of above


Answer: Option A

Explanation:

The file source.txt will be opened in the binary mode.

3. What does fp point to in the program ?

#include<stdio.h>

int main()

{

FILE *fp;

fp=fopen("trial", "r");

return 0;

}

A. The first character in the file

B. A structure which contains a char pointer which points to the first character of a file.

C. The name of the file.

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D. The last character in the file.


Answer: Option B

Explanation:

The fp is a structure which contains a char pointer which points to the first character of a file.

4. Which of the following operations can be performed on the file "NOTES.TXT" using the below code?

FILE *fp;

fp = fopen("NOTES.TXT", "r+");

A. Reading B. Writing

C. Appending D. Read and Write


Answer: Option D

Explanation:

r+ Open an existing file for update (reading and writing).

5. To print out a and b given below, which of the following printf() statement will you use?

#include<stdio.h>

float a=3.14;

double b=3.14;

A. printf("%f %lf", a, b);

B. printf("%Lf %f", a, b);

C. printf("%Lf %Lf", a, b);

D. printf("%f %Lf", a, b);


Answer: Option A

Explanation:

To print a float value, %f is used as format specifier.

To print a double value, %lf is used as format specifier.

Therefore, the answer is printf("%f %lf", a, b);

6. Which files will get closed through the fclose() in the following program?

#include<stdio.h>

int main()

{

FILE *fs, *ft, *fp;

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fp = fopen("A.C", "r");

fs = fopen("B.C", "r");

ft = fopen("C.C", "r");

fclose(fp, fs, ft);

return 0;

}

A. "A.C" "B.C" "C.C" B. "B.C" "C.C"

C. "A.C" D. Error in fclose()


Answer: Option D

Explanation:

Extra parameter in call to fclose().

7. On executing the below program what will be the contents of 'target.txt' file if the source file contains a

line "To err is human"?

#include<stdio.h>

int main()

{

int i, fss;

char ch, source[20] = "source.txt", target[20]="target.txt", t;

FILE *fs, *ft;

fs = fopen(source, "r");

ft = fopen(target, "w");

while(1)

{

ch=getc(fs);

if(ch==EOF)

break;

else

{

fseek(fs, 4L, SEEK_CUR);

fputc(ch, ft);

}

}

return 0;

}

A. r n B. Trh

C. err D. None of above


Answer: Option B

Explanation:

The file source.txt is opened in read mode and target.txt is opened in write mode. The file source.txt

contains "To err is human".

Inside the while loop,

ch=getc(fs); The first character('T') of the source.txt is stored in variable ch and it's checked for EOF.

if(ch==EOF) If EOF(End of file) is true, the loop breaks and program execution stops.

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If not EOF encountered, fseek(fs, 4L, SEEK_CUR); the file pointer advances 4 character from the

current position. Hence the file pointer is in 5th character of file source.txt.

fputc(ch, ft); It writes the character 'T' stored in variable ch to target.txt.

The while loop runs three times and it write the character 1st and 5th and 11th characters ("Trh") in the

target.txt file.

8. To scan a and b given below, which of the following scanf() statement will you use?

#include<stdio.h>

float a;

double b;

A. scanf("%f %f", &a, &b); B. scanf("%Lf %Lf", &a, &b);

C. scanf("%f %Lf", &a, &b); D. scanf("%f %lf", &a, &b);


Answer: Option D

Explanation:

To scan a float value, %f is used as format specifier.

To scan a double value, %lf is used as format specifier.

Therefore, the answer is scanf("%f %lf", &a, &b);

9. Out of fgets() and gets() which function is safe to use?

A. gets() B. fgets()


Answer: Option B

Explanation:

Because, In fgets() we can specify the size of the buffer into which the string supplied will be stored.

10. Consider the following program and what will be content of t?

#include<stdio.h>

int main()

{

FILE *fp;

int t;

fp = fopen("DUMMY.C", "w");

t = fileno(fp);

printf("%d\n", t);

return 0;

}

A. size of "DUMMY.C" file

B. The handle associated with "DUMMY.C" file

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C. Garbage value

D. Error in fileno()


Answer: Option B

Explanation:

fp = fopen("DUMMY.C", "w"); A file DUMMY.C is opened in write mode and returns the file

pointer to fp

t = fileno(fp); returns the handle for the fp stream and it stored in the variable t

printf("%d\n", t); It prints the handle number.

Find Output of Program

1. What will be the content of 'file.c' after executing the following program?

#include<stdio.h>

int main()

{

FILE *fp1, *fp2;

fp1=fopen("file.c", "w");

fp2=fopen("file.c", "w");

fputc('A', fp1);

fputc('B', fp2);

fclose(fp1);

fclose(fp2);

return 0;

}

A. B B.

A

B

C.

B

B D. Error in opening file 'file1.c'


Answer: Option A

Explanation:

Here fputc('A', fp1); stores 'A' in the file1.c then fputc('B', fp2); overwrites the contents of the file1.c

with value 'B'. Because the fp1 and fp2 opens the file1.c in write mode.

Hence the file1.c contents is 'B'.

2. What will be the output of the program ?

#include<stdio.h>

int main()

{

int k=1;

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printf("%d == 1 is" "%s\n", k, k==1?"TRUE":"FALSE");

return 0;

}

A. k == 1 is TRUE B. 1 == 1 is TRUE

C. 1 == 1 is FALSE D. K == 1 is FALSE


Answer: Option B

Explanation:

Step 1: int k=1; The variable k is declared as an integer type and initialized to '1'.

Step 2: printf("%d == 1 is" "%s\n", k, k==1?"TRUE":"FALSE"); becomes

=> k==1?"TRUE":"FALSE"

=> 1==1?"TRUE":"FALSE"

=> "TRUE"

Therefore the output of the program is 1 == 1 is TRUE


#include<stdio.h>

char *str = "char *str = %c%s%c; main(){ printf(str, 34, str, 34);}";

int main()

{

printf(str, 34, str, 34);

return 0;

}

A. char *str = "char *str = %c%s%c; main(){ printf(str, 34, str, 34);}"; main(){ printf(str, 34, str, 34);}

B. char *str = %c%s%c; main(){ printf(str, 34, str, 34);}

C. No output

D. Error in program


Answer: Option A

4. If the file 'source.txt' contains a line "Be my friend" which of the following will be the output of below

program?

#include<stdio.h>

int main()

{

FILE *fs, *ft;

char c[10];

fs = fopen("source.txt", "r");

c[0] = getc(fs);

fseek(fs, 0, SEEK_END);

fseek(fs, -3L, SEEK_CUR);

fgets(c, 5, fs);

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puts(c);

return 0;

}

A. friend B. frien

C. end D. Error in fseek();


Answer: Option C

Explanation:

The file source.txt contains "Be my friend".

fseek(fs, 0, SEEK_END); moves the file pointer to the end of the file.

fseek(fs, -3L, SEEK_CUR); moves the file pointer backward by 3 characters.

fgets(c, 5, fs); read the file from the current position of the file pointer.

Hence, it contains the last 3 characters of "Be my friend".

Therefore, it prints "end".


#include<stdio.h>

int main()

{

float a=3.15529;

printf("%2.1f\n", a);

return 0;

}

A. 3.00 B. 3.15

C. 3.2 D. 3


Answer: Option C

Explanation:

float a=3.15529; The variable a is declared as an float data type and initialized to value 3.15529;

printf("%2.1f\n", a); The precision specifier tells .1f tells the printf function to place only one number

after the .(dot).

Hence the output is 3.2


#include<stdio.h>

int main()

{

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printf("%c\n", ~('C'*-1));

return 0;

}

A. A B. B

C. C D. D


Answer: Option B


#include<stdio.h>

int main()

{

FILE *fp;

unsigned char ch;

/* file 'abc.c' contains "This is Saikat12 " */

fp=fopen("abc.c", "r");

if(fp == NULL)

{

printf("Unable to open file");

exit(1);

}

while((ch=getc(fp)) != EOF)

printf("%c", ch);

fclose(fp);

printf("\n", ch);

return 0;

}

A. This is Saikat12 B. This is

C. Infinite loop D. Error


Answer: Option C

Explanation:

The macro EOF means -1.

while((ch=getc(fp)) != EOF) Here getc function read the character and convert it to an integer value

and store it in the variable ch, but it is declared as an unsigned char. So the while loop runs infinitely.


#include<stdio.h>

int main()

{

char *p;

p="%d\n";

p++;

p++;

printf(p-2, 23);

return 0;

}

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A. 21 B. 23

C. Error D. No output


Answer: Option B


#include<stdio.h>

int main()

{

FILE *ptr;

char i;

ptr = fopen("myfile.c", "r");

while((i=fgetc(ptr))!=NULL)

printf("%c", i);

return 0;

}

A. Print the contents of file "myfile.c"

B. Print the contents of file "myfile.c" upto NULL character

C. Infinite loop

D. Error in program


Answer: Option C

Explanation:

The program will generate infinite loop. When an EOF is encountered fgetc() returns EOF. Instead of

checking the condition for EOF we have checked it for NULL. so the program will generate infinite loop.


#include<stdio.h>

int main()

{

printf("%%%%\n");

return 0;

}

A. %%%%% B. %%

C. No output D. Error


Answer: Option B


#include<stdio.h>

int main()

{

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int a=250;

printf("%1d\n", a);

return 0;

}

A. 1250 B. 2

C. 50 D. 250


Answer: Option D

Explanation:

int a=250; The variable a is declared as an integer type and initialized to value 250.

printf("%1d\n", a); It prints the value of variable a.

Hence the output of the program is 250.


#include<stdio.h>

int main()

{

FILE *fp;

char ch, str[7];

fp=fopen("try.c", "r"); /* file 'try.c' contains "This is Nagpur" */

fseek(fp, 9L, SEEK_CUR);

fgets(str, 5, fp);

puts(str);

return 0;

}

A. agpur B. gpur

C. Nagp D. agpu


Answer: Option D

13. What will be the output of the program if value 25 given to scanf()?

#include<stdio.h>

int main()

{

int i;

printf("%d\n", scanf("%d", &i));

return 0;

}

A. 25 B. 2

C. 1 D. 5


Answer: Option C

Explanation:

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The scanf function returns the number of input is given.

printf("%d\n", scanf("%d", &i)); The scanf function returns the value 1(one).

Therefore, the output of the program is '1'.

Point Out Errors

1. Point out the error in the program?

#include<stdio.h>

#include<stdlib.h>

int main()

{

unsigned char;

FILE *fp;


if(!fp)

{

printf("Unable to open file");

exit(1);

}

fclose(fp);

return 0;

}

A. Error: in unsigned char statement

B. Error: unknown file pointer

C. No error

D. None of above


Answer: Option C

Explanation:

This program tries to open the file trial.txt in read mode. If file not exists or unable to read it prints

"Unable to open file" and then terminate the program.

If file exists, it simply close the file and then terminates the program.


#include<stdio.h>

int main()

{

char ch;

int i;

scanf("%c", &i);

scanf("%d", &ch);

printf("%c %d", ch, i);

return 0;

}

A. Error: suspicious char to in conversion in scanf()

B. Error: we may not get input for second scanf() statement

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C. No error

D. None of above


Answer: Option B


#include<stdio.h>

int main()

{

FILE *fp;


fseek(fp, "20", SEEK_SET);

fclose(fp);

return 0;

}

A. Error: unrecognised Keyword SEEK_SET

B. Error: fseek() long offset value

C. No error

D. None of above


Answer: Option B

Explanation:

Instead of "20" use 20L since fseek() need a long offset value.


#include<stdio.h>

/* Assume there is a file called 'file.c' in c:\tc directory. */

int main()

{

FILE *fp;

fp=fopen("c:\tc\file.c", "r");

if(!fp)

printf("Unable to open file.");

fclose(fp);

return 0;

}

A. No error, No output.

B. Program crashes at run time.

C. Output: Unable to open file.

D. None of above


Answer: Option C

Explanation:

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The path of file name must be given as "c:\\tc\file.c"

5. Point out the error/warning in the program?

#include<stdio.h>

int main()

{

unsigned char ch;

FILE *fp;


while((ch = getc(fp))!=EOF)

printf("%c", ch);

fclose(fp);

return 0;

}

A. Error: in unsigned char declaration

B. Error: while statement

C. No error

D. It prints all characters in file "trial"


Answer: Option A

Explanation:

Here, EOF is -1. As 'ch' is declared as unsigned char it cannot deal with any negative value.

Point Out Correct Statements

1. Which of the following statement is correct about the program?

#include<stdio.h>

int main()

{

FILE *fp;

char ch;

int i=1;

fp = fopen("myfile.c", "r");

while((ch=getc(fp))!=EOF)

{

if(ch == '\n')

i++;

}

fclose(fp);

return 0;

}

A. The code counts number of characters in the file

B. The code counts number of words in the file

C. The code counts number of blank lines in the file

D. The code counts number of lines in the file


Answer: Option D

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Explanation:

This program counts the number of lines in the file myfile.c by counting the character '\n' in that file.

2. Which of the following statement is correct about the program?

#include<stdio.h>

int main()

{

FILE *fp;

char str[11], ch;

int i=0;

fp = fopen("INPUT.TXT", "r");

while((ch=getc(fp))!=EOF)

{

if(ch == '\n' || ch == ' ')

{

str[i]='\0';

strrev(str);

printf("%s", str);

i=0;

}

else

str[i++]=ch;

}

fclose(fp);

return 0;

}

A. The code writes a text to a file

B. The code reads a text files and display its content in reverse order

C. The code writes a text to a file in reverse order

D. None of above


Answer: Option B

Explanation:

This program reads the file INPUT.TXT and store it in the string str after reversing the string using

strrev function.

3. Point out the correct statements about the program?

#include<stdio.h>

int main()

{

FILE *fptr;

char str[80];

fptr = fopen("f1.dat", "w");

if(fptr == NULL)

printf("Cannot open file");

else

{

while(strlen(gets(str))>0)

{

fputs(str, fptr);

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fputs("\n", fptr);

}

fclose(fptr);

}

return 0;

}

A. The code copies the content of one file to another

B. The code writes strings that are read from the keyboard into a file.

C. The code reads a file

D. None of above


Answer: Option B

Explanation:

This program get the input string from the user through gets function and store it in the file f1.txt using

fputs function.

True / False Questions

1. While calling the fprintf() function in the format string conversion specifier %s can be used to write a

character string in capital letters.

A. True B. False


Answer: Option B

Explanation:

The %s format specifier tells the compiler the given input was string of characters.

2. A text stream is an ordered sequence of characters composed into lines, each line consisting of zero or

more characters plus a terminating new-line character.

A. True B. False


Answer: Option A

Explanation:

True, each line may contain zero or more characters terminated by a newline character.

3. Offset used in fseek() function call can be a negative number.

A. True B. False


Answer: Option A

Explanation:

True, offset in fseek() function can be a negative number. It makes the file pointer to move backwards

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from the current position.

Declaration: retval = fseek( fp, offset, from );

Where:

FILE *fp; = points to the file on which I/O is to be repositioned.

long offset; = is an integer giving the number of bytes to move forward or backward in the file. This

may be positive or negative.

int from; = is one of the manifests SEEK_SET, SEEK_CUR, or SEEK_END.

int retval; = is non-zero if the seek operation was invalid (e.g. on a file not opened with a "b" option);

otherwise, the return value is zero.

4. We should not read after a write to a file without an intervening call to fflush(), fseek() or rewind()

A. True B. False


Answer: Option A

Explanation:

True, we should not be able to read a file after writing in that file without calling the below functions.

int fflush ( FILE * stream ); If the given stream was open for writing and the last i/o operation was an

output operation, any unwritten data in the output buffer is written to the file.

int fseek ( FILE * stream, long int offset, int origin ); Its purpose is to change the file position indicator

for the specified stream.

void rewind ( FILE * stream ); Sets the position indicator associated with stream to the beginning of

the file.

5. In a call to printf() function the format specifier %b can be used to print binary equivalent of an

integer.

A. True B. False


Answer: Option B

Explanation:

There is no format specifier named %b in c.

Yes / No Questions

1. stderr, stdin, stdout are FILE pointers

A. Yes B. No

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Answer: Option A

Explanation:

Yes, these will be declared like

The corresponding stdio.h variable is FILE* stdin;

The corresponding stdio.h variable is FILE* stdout;

The corresponding stdio.h variable is FILE* stderr;

2. A file written in text mode can be read back in binary mode.

A. Yes B. No


Answer: Option B

Explanation:

The difference is that text files contain lines (or records) of text and each of these has an end-of-line

marker automatically appended to the end of it whenever you indicate that you have reached the end of

a line.

Binary files are not broken up into separate lines or records so the end-of line marker is not written

when writing to a binary file.

So, we cannot read the correct the data in binary mode.

3. Will the following program work?

#include<stdio.h>

int main()

{

int n=5;

printf("n=%*d\n", n, n);

return 0;

}

A. Yes B. No


Answer: Option A

Explanation:

It prints n= 5

4. Can we specify a variable filed width in a scanf() format string?

A. Yes B. No


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Answer: Option B

Explanation:

In scanf() a * in a format string after a % sign is used for the suppression of assignment. That is, the

current input field is scanned but not stored.

END

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Input / Output - · PDF fileInput / Output General Questions 1 ... FILE *stream); fgets reads characters from stream into the string s ... The while loop runs three times and it write