difference between float and double
This tip submitted by ankit panwar on 2012-03-10 01:14:36. It has been viewed 15743 times.
Rating of 8.1 with 80 votes
In c++ any value like 4.12 is treated as a double by default.
Comparing floats and doubles can be a tricky business because of the difference in precision leading to minute errors. For example:
float a = 4.12;
if(a==4.12)
{
cout<<"hello";
}
else
{
cout<<"bye "<
This will show you the output as "bye 4.12"
Why?
Because by default 4.12 is a double (such as in the if statement or in the assignment to our variable), but storing it in a float it loses some precision, and so comparing then comparing a double with a float lead to microscopic changes in the precision of the number--remember that floats and doubles are not precise.
Two lessons here: one is that floating point numbers shouldn't be compared directly most of the time, and the other is that the default size and type of a hard-coded floating point number is double.
For more on floating point numbers, read understanding floating point numbers--accuracy and precision.
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