A strange output for a simple code

[ittoop]

Dear All,
When I am trying to convert a string ( "1000.01" ) to a floating pointumber and multiply the value by 100. I get the output as below. I am using Arduino Mega2560 board with Arduino IDE version 1.8.19. My code is given at the end of this post.

Output:
dummy_float:1000.01
dummy:100000

If I repeat this with another string in the atof function the output was as shown below. The code is attached for your kind reference. Please help.

Case1:
String : "1000.02"
dummy_float:1000.02
dummy:100001

Case2:
String : "1000.03"
dummy_float:1000.03
dummy:100003

Code:

#include <stdio.h>
#include <stdlib.h>
void setup() {

unsigned long dummy;
float dummy_float;
   Serial.begin(9600);
   dummy_float=atof("1000.01");
   dummy=(float)dummy_float*100.0;

   Serial.print("\n");
   Serial.print(dummy_float);
   Serial.print("\n");
   Serial.print(dummy);
}

void loop() {
}

[anon56112670]

Can you say what it is that is "strange"?

[build_1971]

Perhaps you want:

dummy = uint32_t (dummy_float*100.0);

Or does that yield the same result?

[ruilviana]

Hi,
Floating point numbers may not be exactly what you see.
Try this code and see the result:

#include <stdio.h>
#include <stdlib.h>
void setup() {

unsigned long dummy;
float dummy_float;
   Serial.begin(9600);
   dummy_float=atof("1000.01");
   dummy=(float)dummy_float*10000.0;

   Serial.print("\n");
   Serial.print(dummy_float,6);
   Serial.print("\n");
   Serial.print(dummy);
}

void loop() {
}

1000.009948
10000099

type or paste code here

[ittoop]

Thank you all for your fast reply.
ruilviana's solution worked.
Since I need only two decimal places I have modified the line as follows.

dummy=(dummy_float+0.001)*100.0;

Modified code:

#include <stdio.h>
#include <stdlib.h>
void setup() {

unsigned long dummy;
float dummy_float;
   Serial.begin(9600);
   dummy_float=atof("1000.01");
   dummy=(dummy_float+0.001)*100.0;

   Serial.print("\n");
   Serial.print(dummy_float);
   Serial.print("\n");
   Serial.print(dummy);
}

void loop() {
}