Green goblin - 4 months ago 29

C Question

How would you divide a number by 3 without using

`*`

`/`

`+`

`-`

`%`

The number may be signed or unsigned.

Answer

This is a simple function which performs the desired operation.But it requires `+`

operator, so all you have to do is to add the values with the bit-operators:

```
// replaces the + operator
int add(int x, int y) {
while(x) {
int t = (x & y) <<1;
y ^= x;
x = t;
}
return y;
}
int divideby3 (int num) {
int sum = 0;
while (num > 3) {
sum = add(num >> 2, sum);
num = add(num >> 2, num & 3);
}
if (num == 3)
sum = add(sum, 1);
return sum;
}
```

As Jim commented this works because:

`n = 4 * a + b`

`n / 3 = a + (a + b) / 3`

`So sum += a, n = a + b`

, and iterateWhen

`a == 0 (n < 4)`

,`sum += floor(n / 3);`

i.e. 1,`if n == 3, else 0`