Bitwise Operations, C (gcc)

Language: Layout:

/*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;

printf("Please input an integer value: ");
   
   // use % d for decimal
   // use % x for hex
   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);
   
   // IN CLASS *****************************************************
   
   // imagine a = 123 and you want lowest digit ==> use mod 10 to get down to lowest number
   // now write a few lines of code that gives the least significant byte of a as an integer or char
   // a = 0xabcd1234  output = 0x34
   // a = -1 = 0xffffffff then output = 0xff
   
   int temp = a % 256;         // 2^8 = 256
   printf("Hex: 0x%x\n", temp);
 
   
   
   // now give four bits starting from bit postion 3
   // shift to the right three times and mask the extra 
   // & operation can be used to force some bits to 0
   // the mask that you need has 0s on those bits and 1s on the rest
   
   // shift
   int temp2 = a >> 3;
   // mask
   temp2 = temp2 & 0xf;     // 0xf is called the mask
   printf("Hex: 0x%x\n", temp2);
   
   
   
   // now set the bits 4, 5 and 6 to 1, leave the rest of the bits unchanged
   // create a new number with 1s where you want them, and 0s for the other bits
   // 00...00 0111 0000 = 0x70
   
   int temp3 = a | 0x70;
   
   // ****************************************************************
   
   return 0;
}

Show compiler warnings [ + ] Compiler args [ - ] Show input
Compilation time: 0.12 sec, absolute running time: 0.14 sec, cpu time: 0 sec, memory peak: 3 Mb, absolute service time: 0,35 sec