bitwise_operation__end-of-class, C (gcc)

bitwise_operation__end-of-class

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

#include "stdio.h"

//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
       // temp % 2 allows the program to decide if the value at location k in binary, where k = 31-i, is ASCII 48 (0) or ASCII 49 (1),
       //     converting that number to binary.
       // k = 31 - i because we want to work with the LSB.
        
       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;

printf("Please input an integer value: ");
   scanf("%d", &a);
   printf("\nDecimal: %d\n", a);
   printf("Hex: %x\n", a);
   
   char binary[33];
   DecimalToBinary(a, binary);
   printf ("Binary: %s\n", binary);
   
    
   // making something 1, so use OR.  Do not use AND. 
   
   // reset the LSB to 0 and leave the rest of the bits unchanged.
   // print the result in hex and binary.
    
   int temp;
   //0xfffffffe in this operation is called a "mask".
   temp = a & 0xfffffffe;
   printf("Hex: 0x%x\n", temp);
   DecimalToBinary(temp, binary);
   printf("Binary: %s\n", binary);
    
   // set the MSB of a to 1 and leave the rest of the bits unchanged.
   // print the result in hex and binary.
   
   // 1000 = 8.
   temp = a | 0x80000000;
   printf("Hex: 0x%x\n", temp);
   DecimalToBinary(temp, binary);
   printf("Binary: %s\n", binary);
   
   
   return 0;
}


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