Embedded C Interview Questions with Answers | Part 4

Square of Number Without Using * Operator in C

#include <stdio.h>
#include "stdafx.h"
#include "conio.h"

int square(int x)
{
    int i = (x-1);
    int orgx = x;
    while(i--)
    {   
        x=x+orgx;
    }
    return x;
}

#define SQR(x)    {int i = x;                            \
                 int res = 0;                        \
                 while(i--){                        \
                    res = res + x;}                    \
                 x=res;}
                
                

int getSquare(int x)
{
    int i = x;
    int res = 0;
    while(i--)
    {   
        res=res+x;
    }
    return res;
}
            

int main()
{
    printf("Hello, World!\n");
    int a = 7;
    printf("%d\n",square(a));
    printf("%d\n",getSquare(a));
    SQR(a);
    printf("%d\n",a);
    getch();
}

Output:
Hello, World!
49
49
49

Divide the Number With 9 Without Using  / * % Operator in C

#include "stdafx.h"
#include <conio.h>
#include <stdio.h>

int checkDivby9(int x)
{
    int status = 0, ans = 0;
    int divby8;
    
    if(x < 9)
        status = 0;

    while(x >= 72)
    {
        x = x - 72;
        ans = ans + 8;
    }

    divby8 = x >> 3;
    //printf("%d\n",divby8);
    //printf("%d\n",x);
    
    if(divby8 == (x-(divby8 << 3)))
    {
        status = 1;
        ans = ans + divby8;        
    }
    //printf("%d\n",ans);
    return status;
}

int _tmain(int argc, _TCHAR* argv[])
{
    printf("Hello, World!\n");
    int a;

    a = 36;
    if(checkDivby9(a))
    printf("%d is divisible by 9\n", a);

    a = 80;
    if(checkDivby9(a))
    printf("%d is divisible by 9\n", a);

    a = 90;
    if(checkDivby9(a))
    printf("%d is divisible by 9\n", a);

    a = 108;
    if(checkDivby9(a))
    printf("%d is divisible by 9\n", a);

    a = 4500;
    if(checkDivby9(a))
    printf("%d is divisible by 9\n", a);
     getch();

    return 0;
}

OutPut:
Hello, World!
36 is divisible by 9
90 is divisible by 9
108 is divisible by 9
4500 is divisible by 9

How to Check Weather Number is Power of 2 | Optimize Method

It is very much easy to check the power of 2.  If you observe the pattern for the different numbers.

For example: 

3 = 11
4 = 100

7  = 111
8 = 1000

15 = 1111
16 = 10000

31 = 11111
32 = 100000

Observe that both numbers carefully. You can see if you do anding of both the numbers then result will be zero. 

Example 3 & 4 = 0.

#include "stdafx.h"
#include "stdio.h"
#include "conio.h"
#include "string.h"
#include "stdlib.h"

int _tmain(int argc, _TCHAR* argv[])
{
    int chPow2 = 30;
    if((chPow2 & (chPow2 - 1)) == 0)
        printf("Number: %d is power of 2", chPow2);
    else
        printf("Number: %d is not power of 2", chPow2);

    getch();

    return 0;
}