How does ANSI C convert a float number to scientific notation?

It converts a float number to scientific notation using the format

[sign] d.ddd e[sign]ddd

where d represents a digit, the digits before the decimal point represent the field width, and the digits after the decimal point represent the specified precision. Note that a number in this form is equivalent to

[sign] d.ddd x 10^([sign]ddd)

For example, when we use the format %15.4e, that is, field width = 15 and precision = 4, to display the number

123456789.12

in scientific notation, we get

bbbb1.2346e+009

(where b represents blank), which is equivalent to

1.2346 x 10^9

or

1234600000.0

On display, we lose some accuracy because the specified precision is not high enough. However, the affects the display only. The complete value still is stored in the computer's memory.