C++ Notes: Bit Ops - Convert to hex

This program reads integers and prints them in hexadecimal, using the shift and "and" operators to extract the relevant digits. Note: This requires knowledge of character arrays. The problems require use of functions.

// Read ints and print their hex representations
// Note sizeof(int) returns number of bytes in an int.

#include <iostream>
using namespace std;

void main() {
    int n;
    while (cin >> n) {
        cout << "decimal: " << n << endl;
      
        //--- Print hex with leading zeros
        cout << "hex    : ";
        for (int i=2*sizeof(int) - 1; i>=0; i--) {
            cout << "0123456789ABCDEF"[((n >> i*4) & 0xF)];
        }
        cout << endl << endl;
    }
}

Exercises

Here are some modifications that could be made to this code.

This program writes the digits to cout. A more general solution is to write the conversions as functions which put their output into a character array as c-strings. Write these conversions as functions with the following prototypes:
```
    void intToBinary(char result[], int n);
    void intToHex(char result[], int n);
    
    // A call might look like this:
    char binary[50]; // big enough to hold an int with spaces.
    . . .
    while (cin >> n) {
       intToBinary(binary, n);  // produce binary character string.
       cout << binary << " has " < strlen(binary) 
            << " digits." << endl;
    }
```
There is a big difference between the hex conversion and the binary conversion. The hex conversion writes a char to cout while the binary conversion writes an int. It's necessary to put a char in the output array of the function of course.