How do I fix this convert error? Is this a bug?

Question

I have an integer and it's value is -16777216
I want to convert it to a float once done the float equals -1.677722E+07
Now if I convert the float back at this point everything works and I get a proper result.

However if I manually make the float equal -1.677722E+07 then convert back to int I get
a wrong result of -16777220 what is going on and how do I fix this? Example shown below in c# code.

int i = -16777216;
float f = Convert.ToSingle(i);                        // = -1.677722E+07 (works converting back)
label1.Text = i.ToString();
label2.Text = f.ToString();
f = -1.677722E+07f;                                   //Putting it in as a value makes error result
label3.Text = Convert.ToInt32(f).ToString();   //converting back

Vulpes · Answer

This sort of anomaly often occurs when converting between integral and floating point types and is not a bug as such. Although they may appear to be the same (because they have the same string representation) the float you get when converting -16777216 to float is not the same as the float you get when you assign -1.677722E+07F to a float variable! This can be seen by running the following code: int i = -16777216; float f = Convert.ToSingle(i); float g = -1.677722E+07F; Console.WriteLine( f == g); foreach(byte b in BitConverter.GetBytes(f)) Console.Write({0}  b); Console.WriteLine(); foreach(byte b in BitConverter.GetBytes(g)) Console.Write({0}  b); Console.WriteLine(); The output is : False 0 0 128 203 2 0 128 203 So the two floats differ in the first byte. Double is better than float in this respect as it has a precision of 15 or 16 digits compared to float's 7 digits. However if you're writing an application which can't tolerate this sort of anomaly it's best to use the decimal data type rather than float or double which is stored as a scaled integer accurate to 28 digits. The drawback is that it needs 16 bytes of storage (float requires 4 and double 8) and when doing a lot of calculations is much slower.

insane · Answer

I tried each of the codes above and it still gives -16777220. Are you getting a different result?

Veena Sarda · Answer

The +07f is the problem area. You are not representing the scientific notation correctly. Try as shown in the screenshot Thanks Veena

Manish Dwivedi · Answer

Hi Integer To Float Conversion: int intNo = 2345; float no = intNo; Console .Write(no); // float can handle int because of upcasting Float To Integer Conversion: float floNo = 1.5f; int num = ( int )floNo; // but here .5 value will be lost due to downcasting Console .Write(num); so when you converting back float to int it can be some value loss. this is the concept. i have made some changes to your code. int i = -16777216; float f = Convert.ToSingle(i); // = -1.677722E+07 (works converting back) Label1.Text = i.ToString(); Label2.Text = f.ToString(); //f = -1.677722E+07f; //Putting it in as a value makes error result Label3.Text = ((int)(f)).ToString(); //converting back try this Normal 0 false false false EN-US X-NONE AR-SA /* Style Definitions */ table.MsoNormalTable{mso-style-name:Table Normal;mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-parent:;mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin-top:0in;mso-para-margin-right:0in;mso-para-margin-bottom:10.0pt;mso-para-margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:Calibrisans-serif;mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:Arial;mso-bidi-theme-font:minor-bidi;}