The first day of Camp David

<> It indicates to go to the system directory and find "". It indicates to search for PWD in the current directory to print the current directory. /indicates that the current directory RM indicates removing-I specifies the path of some header files "header. h "first searches for the current (user directory), then searches for the system directory> indicates that the previous output is in the following file. 1. Compile preprocessing (GCC-e source. c> source. e) 2 compile (GCC-S source. e) 3 Assembly (GCC-C source) 4 connection (Link) flt_epsilon indicates the smallest value that float can represent. A smaller number than it can be understood as equal to 0, it satisfies the minimum positive number of X + 1.0 not equal to 1.0. That is to say, all positive numbers x, x + 1.0 = 1.0 smaller than flt_epsilon are true. #-Sharp. Dot # define: macro definition. It defines a symbol and is replaced during preprocessing without consideration. # ifdef/# ifndef/# UNDEF: determines whether to define a macro. In addition, the third variable is not used for interaction between two variable values, for example, a = 3, B = 5.int include <stdio. h> int main () {int A = 3, B = 5; A = a + B; B = A-B; A = A-B; printf ("A = % d B = % d \ n", a, B); Return 0 ;}

The first day of Camp David