How can I perform multiplication without the '*' operator?

Question

I was just going through some basic stuff as I am learning C. I came upon a question to multiply a number by 7 without using the * operator. Basically it\'s like this

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Answer 1

Let N be the number that we want to multiply with 7.

N x 7 = N + N + N + N + N + N + N
N x 7 = N + N + N + N + N + N + N + (N - N)
N x 7 = (N + N + N + N + N + N + N + N) - N
N x 7 = 8xN - N

As we know that, left shifting any number by one bit multiply it by 2. Hence, multiplying any number with 8 is equivalent to right shifting it by 3 bits

N x 7 = (N << 3) - N 

I found this description here http://www.techcrashcourse.com/2016/02/c-program-to-multiply-number-by-7-bitwise-operator.html

Hope it helps.