How to check number?

Question

Could anyone please tell me how to check what number I've got from a * b? Which is I would like to know every part of this number so for example if the result from this expression would be 25 I would like to know that first digit is two and second digit is five.

Answer 1

You have to get the result of the integer division by the appropriate power of ten.

int exp = std::floor( std::log10( num ) );
int first_digit = num / int( std::pow( 10.0, exp ) );

This is an (inefficient) way to get the first digit directly. It would be better to iterate starting from the last.

Answer 2

int val = res;

while( val > 0 )
{
   std::cout << val % 10 << endl; 
   val /= 10;
}

Answer 3

a mod 10 == last digit of a
a / 10 == a without its last digit

So, for 25:

25 % 10 == 5 => 5 is the last digit of 25
25 / 10 == 2
2 % 10 == 2 => 2 is the first digit of 25

You can use these in a while loop to get each digit.

while (num > 0)
{
    digit = num % 10;
    // digit is now the current digit, counting from the right towards the left.
    num /= 10;
}

Answer 4

perhaps a little overkill... but even works with doubles

#include <sstream>
#include <iostream>

int main()
{
    double a = 5.2;
    double b = 7;
    double z = a*b;

    std::stringstream s;
    s << z;

    for (int i = 0; i < s.str().length(); i++)
        std::cout << i << ": " << s.str()[i] << std::endl;

    return 0;
}

Answer 5

char str[30];
sprintf(str,"%d",a*b);
int ndigits = strlen(str);

There you have all digits of your value in the string, and the number of digits in ndigits.

e.g. if a*b = 25 you get

ndigits==2
str[ndigits-1]=='5'
str[ndigits-2]=='2'

What do you want this for?

Answer 6

Just remember, that e.g. 2101 is basically just 2*10^3 + 1*10^2 + 0*10^1 + 1*10^0.

Answer 7

There's probably an underlying misunderstanding here. The result of the multiplication will most likely be 0x00000019. (Number of leading zeroes will differ). The second step, converting it to canonical decimal will yield "25".

It's important to realize that computers, unlike normal humans, don't do their math in decimal but in binary. Hence, if you want to check a property like "last decimal digit of a number", it's not directly available to them.