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• Write a program in C to find whether a number is power of two or not in one line.
• How to find whether a number is power of two or not.

• Any number who is a power of two(let it be N) have only one bit set in it’s binary representation.
  For Example: 4 = 100, 8 = 1000, 16 = 10000, 32 = 100000 etc.
• If we subtract 1 from any power of 2 number then, the set bit becomes unset and all the bits in right side of the originally set bit becomes 1.
  For Example: 4-1 = 011, 8-1 = 0111, 16-1 = 01111, 32-1=011111
• Now, If bitwise and(&) of N and N-1 returns ) means N is a power of 2.
  For Example, 4 & 3 = 100 & 011 = 000

C program to check whether a number is power of two using bitwise operator

#include<stdio.h>
#include<math.h>
 
int main() {
    int num;
     
    printf("Enter an integer\n");
    scanf("%d", &num);
     
    if(num && ((num & (num-1)) == 0)){
        printf("%d is power of 2", num);
    } else {
        printf("%d is not a power of 2", num);
    }
 
    return 0;
}

Output

Enter an integer
16
16 is power of 2

Enter an integer
15
16 is not a power of 2

• Write a C program to read a binary number and find its two’s complement.
• Wap in C to find two complement of a binary number.

Required Knowledge

• C printf and scanf functions
• If Else ladder in C
• For loop in C
• strlen finction in C

Algorithm to find twos complement of a binary number
1. To find the twos complement of a number first find the ones complement by toggling the bits of the number. Change all 1's to 0's and all 0's to 1's.
2. Add binary 1 to the ones complement to get twos complement.

For Example :
Binary Number = 00101011
Ones Complement = 11010100
Twos Complement = 11010101

C program to find two complement of a binary number

#include <stdio.h>  
#include <string.h>  
   
int main() {
    char binaryNumber[100], onesComplement[100], twosComplement[100];
    int counter, error=0, digitCount, carry = 1;   
    /*
     * Take a binary string as input from user
     */
    printf("Enter a Binary Number\n");  
    scanf("%s", binaryNumber);  
   
    /* 
     * To get one's complement, we toggle 
     * 1's to 0's and 0's to 1's
     */
    digitCount = strlen(binaryNumber);
     
 for(counter=0; counter < digitCount; counter++) {  
        if(binaryNumber[counter]=='1') {  
            onesComplement[counter] = '0';  
        } else if(binaryNumber[counter]=='0') {  
            onesComplement[counter] = '1';  
        } else {  
            printf("Error :( ");  
            return 1;
        }  
    }  
    onesComplement[digitCount] = '\0';
     
    /* 
     * Add 1 to the 1's complement. Perform binary addition
     */ 
    for(counter = digitCount-1; counter >= 0; counter--) {  
        if(onesComplement[counter]=='1' && carry==1){
            twosComplement[counter] = '0';  
        } else if(onesComplement[counter]=='0' && carry==1) {  
            twosComplement[counter] = '1';  
            carry = 0;  
        } else {  
            twosComplement[counter] = onesComplement[counter];  
        }  
    }  
    twosComplement[digitCount] = '\0'; 
       
    printf("Two's Complement : %s", twosComplement);  
   
    return 0;  
}

Output

Enter a Binary Number
11100001
Two's Complement : 00011111

• Write a c program to print fibonacci series using recursion

Fibonacci series are the numbers in the following integer sequence
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 ….
the first two numbers in the Fibonacci sequence are 0 and 1, and each subsequent term is the sum of the previous two terms. In mathematical terms, the Nth term of Fibonacci numbers is defined by the recurrence relation:

• fibonacci(N) = Nth term in fibonacci series
• fibonacci(N) = fibonacci(N – 1) + fibonacci(N – 2);
• whereas, fibonacci(0) = 0 and fibonacci(1) = 1

Below program uses recursion to calculate Nth fibonacci number. To calculate Nth fibonacci number it first calculate (N-1)th and (N-2)th fibonacci number and then add both to get Nth fibonacci number.
For Example : fibonacci(4) = fibonacci(3) + fibonacci(2);

C program to print fibonacci series till Nth term using recursion

In below program, we first takes the number of terms of fibonacci series as input from user using scanf function. We are using a user defined recursive function named ‘fibonacci’ which takes an integer(N) as input and returns the N^th fibonacci number using recursion as discussed above. The recursion will terminate when number of terms are < 2 because we know the first two terms of fibonacci series are 0 and 1.In line number 17, we are calling this function inside a for loop to get the N^th term of series.

/*
* C Program to print fibonacci series using recursion
*/
#include <stdio.h>
#include <conio.h>
 
int fibonacci(int term);
int main(){
    int terms, counter;
    printf("Enter number of terms in Fibonacci series: ");
    scanf("%d", &terms);
    /*
     *  Nth term = (N-1)th therm + (N-2)th term;
     */
    printf("Fibonacci series till %d terms\n", terms); 
    for(counter = 0; counter < terms; counter++){
        printf("%d ", fibonacci(counter));
    }
    getch();
    return 0;
}
/*
 * Function to calculate Nth Fibonacci number
 * fibonacci(N) = fibonacci(N - 1) + fibonacci(N - 2);
 */
int fibonacci(int term){
    /* Exit condition of recursion*/
    if(term < 2)
       return term;
    return fibonacci(term - 1) + fibonacci(term - 2);
}

Program Output

Enter number of terms in Fibonacci series: 9
Fibonacci series till 9 terms
0 1 1 2 3 5 8 13 21

Fibonacci series till Nth term using memorization

Recursive program to print fibonacci series is not so efficient because it does lots of repeated work by recalculating lower terms again and again.

For Example:
fibonacci(6) = fibonacci(5) + fibonacci(4);
To calculate fibonacci(5) it will calculate fibonacci(4) and fibonacci(3). Now, while calculating fibonacci(4) it will again calculate fibonacci(3) which we already calculated while calculating fibonacci(5). We can solve this recalculation problem by memorizing the already calculated terms in an array.

In the below program, we are using an integer array named ‘fibonacciArray’ to store the already calculated terms of fibonacci series(N^th term of fibonacci series is stored at fibonacciArray[N-1]). To calculate the N^th term we add the last two fibinacci elements(N-1 and N-2^th element) stored in array. Finally we store the N^th term also in array so that we can use it to calculate next fibonacci elements.

/*
* C Program to print fibonacci series using memorization
*/
#include <stdio.h>
#include <conio.h>
  
int main(){
    int terms, fibonacciArray[100] = {0}, counter;
    printf("Enter number of terms in Fibonacci series: ");
    scanf("%d", &terms);
    /*
     * fibonacciArray[N] = fibonacciArray[N-1] + fibonacciArray[N-2]
     */
    for(counter = 0; counter < terms; counter++){
        if(counter < 2){
            fibonacciArray[counter] = counter;
        } else {
            fibonacciArray[counter] = fibonacciArray[counter-1] +
                fibonacciArray[counter-2];
        }
        printf("%d ", fibonacciArray[counter]);
    }
    getch();
    return 0;
}

Program Output

Enter number of terms in Fibonacci series: 7
Fibonacci series till 7 terms
0 1 1 2 3 5 8

File in C programming language, can be anything from a disk file to a device. C language provide support for opening a file, closing a file, reading data from a file and writing data to a file through a set of standard library functions.

C file handling is designed to work with a number of devices and file formats like printer, screen, keyboard, disk file etc. C file system transforms different devices into a abstract logical device called stream. All streams behaves same irrespective of devices and files. It provides an abstract consistent interface for C program to interact by hiding the details of the device specific implementations. Disk file read function can be used to read data from keyboard as well.

Points to Remember about Streams

• A Stream is a the sequence of bytes of data.
• All Streams behaves similarly. Same code can be used to perform I/O operations of various streams.
• A stream hides the low level device dependent complexities from C program.
• In a C program, all input and Output is done through streams.
• Three streams gets automatically attached when a program starts execution that is
• Standard Input Stream(stdin)
• Standard Output Stream(stdout)
• Standard Error Stream(stderr)
• Keyboard is associated with stdin stream.
• Screen is associated with stdout stream.

FILE Pointer in C

A file pointer is a pointer to a structure of type FILE. A file pointer is associated with stream and manages all Input and Output operations of that stream. The FILE structure contains information which is required to perform any file I/O operations like name of the file, current location of position indicator in file, data transfer bugger, status flag etc.

A file pointer is a bridge between c program and file/stream. We can declare a FILE pointer as follows:

FILE *file;
Facts about FILE Structure

• To perform any I/O operation on file, we need FILE pointer.
• FILE Structure is defined in stdio.h header file.
• FILE Structure contains necessary information about a stream, which is required to perform I/O operation in that stream.
• FILE pointer is an interface for our programs to interact with files.

Opening a File in C

The stdio.h library function fopen() is used to create a new file or open an exiting file.

FILE *fopen(const char *filename, const char *mode);

Function fopen() opens the file whose name is given in the filename argument and associate it with a stream and return a FILE pointer to be used in any future I/O operations on this stream. The fopen function opens a stream in a particular mode, which defines the operations that are allowed on the stream.
Various Modes of Opening a File

Mode	Description
“r”	To read a file. Opens a file for reading. The file must exist.
“w”	To write on a file. Creates an empty file for writing. If a file already exists with same name, its content is removed and the file is considered as a new empty file.
“a”	To append data at the end of file. The file is created if it does not exist.
“r+”	To read and write on an existing file. Opens a file to update both reading and writing. The file must exist.
“w+”	To create a new file for reading and writing.
“a+”	To read and append data on a file.

C Program to Open a File using fopen Function

The following program shows the use of fopen function to open a text file in read mode.

#include <stdio.h>
 
int main(){
   FILE *file;
   int ch;
    
   /* Open a file for reading */
   file = fopen("textFile.txt","r");
   if(file == NULL){
      perror("Error: Unable to open a file");
   } else {
       while(!feof(file)){
          ch = fgetc(file);
          printf("%c", ch);
       }
       fclose(file);
   }
    
   return(0);
}

Output

fopen C Standard library function

Closing a File in C

The stdio.h library function fclose() is used to close a stream that was opened by fopen() function. Before closing a stream it flushes it’s buffer.

int fclose(FILE *stream);

Function fclose closes a stream whose file pointer is passed as argument. If a call to fclose is successful it returns zero, otherwise EOF is returned.

C Program to Close a File using fclose Function

The following program shows the use of fclose function to close a file(stream) after writing a sentence in it.

#include <stdio.h>
 
int main (){
  FILE * pFile;
   
  /* Creates a new file */
  pFile = fopen ("TextFile.txt","w");
  /* Write a sentence in a file */
  fprintf (pFile, "fclose C standard library function");
  /* Close a file */
  fclose (pFile);
   
  return 0;
}

Output

fclose C standard library function

Reading from a File in C

The stdio.h standard library provides a number of functions to read data from a stream.
Functions to read a single character from a file

Function	Description
fgetc()	Reads a character from the given stream.
getc()	Reads a single character from given stream.
getchar()	Reads a single character from stdin stream.

Functions to Read a String from a File

Function	Description
fgets()	Reads a line from given stream and stores it into a character array.
gets()	Reads a line from stdin and stores it into given character array.

Functions to Read Formatted Data from a File

Function	Description
fscanf()	Read formatted data from given stream.
scanf()	Reads formatted data from stdin.

C Program to read formatted data from a file using fscanf function

The following program shows the use of fscanf function to read formatted data from a stream.

#include <stdio.h>
 
int main()
{
   char string[50];
   int val;
   float fval;
   FILE *file;
 
   file = fopen ("textFile.txt", "w+");
   fprintf(file, "%d %f %s", 5, 5.5, "TechCrashCourse.com");
   rewind(file);
 
   fscanf(file, "%d %f %s", &val, &fval, string);
    
   printf("Integer : %d\n", val);
   printf("Floating point number : %f\n", fval);
   printf("String : %s\n", string);
 
   fclose(file);
   return(0);
}

Output

Integer : 5
Floating point number : 5.500000
String : TechCrashCourse.com

Writing to a File in C

The stdio.h standard library provides a number of functions to write data on a stream.

Functions to write a single character on a file

Function	Description
fputc()	Writes a character to the given stream.
putc()	Writes a character to the given stream.
putchar()	Writes a character to stdout stream.

Functions to write a string on a file

Function	Description
fputs()	Writes a string to the given stream excluding the null terminating character.
puts()	Writes a string to stdout stream excluding null terminating character.

Functions to write formatted data on a file

Function	Description
fprintf()	Writes formatted output to a stream.
printf()	Print formatted data to stdout.
vfprintf()	Writes formatted data to a stream using an argument list.
vprintf()	Print formatted data to stdout using an argument list.
vsprintf()	Writes formatted data to a string using an argument list.

C Program to write formatted data on a file

#include <stdio.h>
 
int main (){
   int c, counter = 0;
   FILE *file;
   char *string = "fprintf C Standard Library function";
    
   /* Create a temporary file */
   file = fopen("textFile.txt", "w");
   fprintf(file, "%s", string);
   fclose(file);
    
   /* Opening textFile.txt and printing it's content */
   file = fopen("textFile.txt", "r");
   while(!feof(file)){
       c = fgetc(file);
       printf("%c", c);
   }
    
   return(0);
}

Output

fprintf C Standard Library function

Standard Library function for File Handling in C

There are many file handling functions defined in stdio.h header file. Here is the list of frequently used file handling functions:

Function	Description
clearerr()	Clears error indicators associated with a given stream.
fclose()	Closes the stream and flushes buffers associated with the given stream.
feof()	Checks the end-of-file indicator of the given stream.
ferror()	Checks the error indicator of the given stream.
fflush()	Flushes the content of the given stream.
fgetc()	Gets the next character from the given stream.
fgetpos()	Gets current position of the given stream.
fgets()	Reads a line from given stream and stores it into a character array.
fopen()	Opens a file in the given mode.
fprintf()	Writes formatted output to a stream.
fputc()	Writes a character to the given stream.
fputs()	Writes a string to the given stream excluding the null terminating character.
fread()	Reads data from the given stream and stores it into an array.
freopen()	Reopens a stream with different file or mode.
fscanf()	Read formatted data from given stream.
fseek()	Changes the position indicator of the given stream.
fsetpos()	Sets the position indicator of the given stream.
ftell()	Returns the current position of the given stream.
fwrite()	Writes data from an array to the given stream.