View Compilation Error

0_0_31729805_12488.cpp: In function 'int gauss()':
0_0_31729805_12488.cpp:15:9: error: 'n' was not declared in this scope
     equ=n,var=?;//多少个方程，多少个变量
         ^
0_0_31729805_12488.cpp:15:15: error: expected primary-expression before '?' token
     equ=n,var=?;//多少个方程，多少个变量
               ^
0_0_31729805_12488.cpp:15:16: error: expected primary-expression before ';' token
     equ=n,var=?;//多少个方程，多少个变量
                ^
0_0_31729805_12488.cpp:15:16: error: expected ':' before ';' token
0_0_31729805_12488.cpp:15:16: error: expected primary-expression before ';' token
0_0_31729805_12488.cpp:24:38: error: 'memset' was not declared in this scope
     memset(free_x,true,sizeof(free_x));
                                      ^
0_0_31729805_12488.cpp:30:34: error: 'fabs' was not declared in this scope
             if(sgn(fabs(a[i][col])-fabs(a[max_r][col]))>0)
                                  ^
0_0_31729805_12488.cpp:36:41: error: 'swap' was not declared in this scope
                 swap(a[k][j],a[max_r][j]);
                                         ^