What does "ans += n << count" mean?

Question

// Function for multiplication 
int multiply(int n, int m) 
{   
    int ans = 0, count = 0; 
    while (m) 
    { 
        if (m % 2 == 1)               
            ans += n << count; 

        // increment of place value (count) 
        count++; 
        m /= 2; 
    } 
    return ans; 
}

What does that expression mean? How to rewrite this expression in a more beginner friendly form?

To make it more beginner friendly, just do one operation per line. Store the result of `n << count` in a temporary variable and them `+=` it to `ans`. — Paul Rooney, Sep 20 '19 at 03:36
Possible duplicate of [What are bitwise shift (bit-shift) operators and how do they work?](https://stackoverflow.com/questions/141525/what-are-bitwise-shift-bit-shift-operators-and-how-do-they-work) — phuclv, Sep 20 '19 at 03:42

score 3 · Answer 1 · answered Sep 20 '19 at 04:27

3

The expression ans += n << count; means the same as the following:

int n_shifted = n << count;  /* bitshift n to the left by count bits */
ans = ans + n_shifted;       /* add n_shifted to ans */

answered Sep 20 '19 at 04:27

Elias

913
6
22

score 1 · Answer 2 · answered Sep 20 '19 at 03:31

1

it bitshifts n left by count then adds it to ans

n << 1  =   n * 2
n << 2  =   n * 4
n << 3  =   n * 8
n << 4  =   n * 16

etc

answered Sep 20 '19 at 03:31

Keith Nicholas

43,549
15
93
156

What does "ans += n << count" mean?

2 Answers2