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

Think about the normal multiplication method we use

         1101 x        =>13
         0101          =>5
---------------------
         1101
        0000
       1101
      0000
===================        
      1000001 .        => 65

Writing the same above in the code

#include

int multiply(int a, int b){
    int res = 0,count =0;
    while(b>0) {
        if(b & 0x1)
            res = res + (a << count);
        b = b>>1;
        count++;
    }
    return res;
}
int main() {
    printf("Sum of x+y = %d", multiply(5,10));
    return 0;
}