Excel18-bit numeric type conversion C # type 1. problem description when reading Excel, numbers such as ID card mobile phone numbers or other numeric types will be converted to 1.000E + 17 in normal Excel mode or other similar numbers. When C # reads and converts data, it can be as follows: the 11-digit mobile phone number can be directly read or converted to the int type. However, if the 18-digit ID card exceeds the maximum value of the int type, the double type conversion is required. solution: If the ID card is in the text mode in Excel, for example, 1111111111111111111, you can directly use [csharp] string s = long. parse ("11111111111111111 "). toString (); if it is a regular mode in Excel, for example, 1.1111E + 17, the above method will report an error because the Parse method uses the default parsing format of the Integer type, the parameter format can be specified to solve [csharp] string s = long. parse ("11111111111111111", System. globalization. numberStyles. float ). toString ();