在第一章中已经介绍过，Ｃ源程序是由函数组成的。 虽然在前面各章的程序中都只有一个主函数main()， 但实用程序往往由多个函数组成。-In the first chapter has been introduced, C source code is a function of composition. While in the earlier chapters of the program is only one main function main (), but the utility is often composed of multiple functions.