Bitwise Operations , C (gcc)

Bitwise Operations

/*Simple program showing how to read an integer and printing it to output in different formats.*/

#include "stdio.h"

// write a function that gets an integer and a mask and returns the result  of using the mask to reset some bits to 0
int ResetBits(int a, int mask) {
  return (a & mask);
}

//converts decimal value to a string that represents the binary number
//note that decimal is already represented in binary in the memory
//all we need is an array of characters 0 and 1 that show the number in binary
int DecimalToBinary(int decimal, char *binary) {

unsigned int temp = decimal;
    int i;
    for (i=0; i<32; i++) {
    
       //ASCII code for '0' is 48 and for '1' is 49
       
       //the bit we calculate in this loop is Least Significant Bit (LSB), so the index is 31-i
       binary[31-i] = 48+ temp % 2;
       
       //dividing by 2, simply shifts the number to right and allows us to process the next bit 
       temp = temp / 2;
       }
       
    //an end is put at the end of binary string. Again this is not a number, but an array of '0's and '1's   
    binary [32] = 0;
 }

int main(void) 
{
   int a;
   int temp;

printf("Please input an integer value: ");
   scanf("%d", &a);
   printf("\nDecimal: %d\n", a);
   printf("Hex: 0x%x\n", a);
   
   char binary[33];
   DecimalToBinary(a, binary);
   printf ("Binary: %s\n", binary);
   
    //write a few lines of code that gives the lowest significant byte (8 bits) as an int or char
    //a=0xabcd1234 output = 0x34
    //if a=-1=ffffffff output=0xff
   
   temp = a % 256; //2^(number of bits you want out) %2 gives 1 bit, %4 for 2 bits, %8 for 3 and so on
   printf ("Hex: 0x%x\n", temp);
    
    //give four bits starting from bit position 3
    
    //temp = a >> 3; //right shift 3 times 
    //temp = temp & 0xf; //this is called masking, all unwanted bits become 0 and wanted bits stay the same 
    temp = ( a >> 3) && 0xf; //top two lines into one 
    printf("Hex: 0x%x\n", temp);
    
    //& operation can be used to force some bits to 0
    //the mask you need has 0 on those bits and 1 on the rest 
    
    //sets the bits 4, 5 and 6 to 1 and leave the rest of the bits unchanged 
    temp = a | 0x70; //another kind of mask with or gate to force a 1 
    printf ("Hex: 0x%x\n", temp);
    DecimalToBinary(temp, binary);
    printf("Binary: %s\n", binary);

return 0;
}


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