精确数字后的“随机”数字

Question

I'm trying to make IF condition where I'm trying to print some text when number is 'correct'. The question is what if the condition can't have 'exact number' ? Like when you are finding everything (*) in linux system "find / -name *.mp3".

Here is my code, sure it do not work work for bad syntax but I put it here for example about my question:

#include <iostream>

int main() {
        double b = 6.922083e-07;
        if (b == 6.922.*e-07) {
                printf("LOL \n");
        }
}

.* by this I mean everything other which do not matter.

Thank you very much, will be happy as an elephant if you can help me. I'm stupid and I just can't find it on google.

Answer 1

You can write a function to automate the task of getting the exponent:

int get_expo(double num){
  int n = 0;
  double number = num;
  if(number > 1 && number !=0){
      while (number > 1){
          number/=10;
          n++;
      }
      n-=1;
   }else{
       while(number < 1){
            number*=10;
            n++;
       }
       n = -n;
  }
  return n;
}

And then you can multiply that number by the 10^ exponent plus 3 if you want three digit precision and then convert it to int :

#include <math.h>
int converted_num = d*pow(10 , get_expo(d) + 3);
if(converted_num == 6922)
{
   //Do something
}

Note that I used 6922 instead of 6.922

Answer 2

If you want "close enough" to be 1e-8, for example:

double eps = 1.0e-8;
if (b > (6.922083e-07 - eps) && b < (6.922083e-07 + eps)) {
    printf("LOL \n");
}