C语言实现，自定义两个函数，实现int型和字符串String型互换：把字符串转化成double浮点型，把int型转化为String型，在网络通信中用得到,在VC环境下已经验证-by using C Language,define two functions and realize below function:we can convert int to string ,and also string to int ,these fucntion has been tested.