C language macro definition

• Constants can be named using a feature called macro definition :#define INCHES_PER_POUND166（ there #define It's preprocessing instructions ）. When compiling a program , The preprocessor will replace each macro with the value it represents .
  weight = (volume + INCHES_PER_POUND -1)/INCHES_PER_POUND;
  Will be
  weight = (volume + 166-1)/ 166;
• Be careful , The name of the macro uses only capital letters . This is the majority C The specifications that programmers follow , But it is not C Requirements of language itself .