/in/foo.cc:1:34: error: #include expects "FILENAME" or <FILENAME>
 #include //引入标准C头文件
                                  ^
/in/foo.cc:3:27: error: #include expects "FILENAME" or <FILENAME>
 #include //引入数学库
                           ^
/in/foo.cc:5:30: error: #include expects "FILENAME" or <FILENAME>
 #include //引入字符串库
                              ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:17:23: error: 'scanf' was not declared in this scope
 scanf("%[^=]=%s",lv,rv);//输入左右两边
                       ^
/in/foo.cc:25:17: error: 'strlen' was not declared in this scope
 while (strlen(lv))
                 ^
/in/foo.cc:31:23: error: 'sscanf' was not declared in this scope
 sscanf(lv,"%[+-]",symb);//输入符号
                       ^
/in/foo.cc:33:32: error: 'sprintf' was not declared in this scope
 sprintf(lv,"%s",lv+(symb[0]!=0));//更新
                                ^
/in/foo.cc:75:17: error: 'strlen' was not declared in this scope
 while (strlen(rv))
                 ^
/in/foo.cc:81:23: error: 'sscanf' was not declared in this scope
 sscanf(rv,"%[+-]",symb);//输入符号
                       ^
/in/foo.cc:83:32: error: 'sprintf' was not declared in this scope
 sprintf(rv,"%s",rv+(symb[0]!=0));//更新
                                ^
/in/foo.cc:137:40: error: 'printf' was not declared in this scope
 if (COEF[0]==0) printf("181818181818\n");
                                        ^
/in/foo.cc:139:18: error: 'printf' was not declared in this scope
 else printf("0\n");
                  ^
/in/foo.cc:147:36: error: 'printf' was not declared in this scope
 printf("1\n%.5f\n",-COEF[0]/COEF[1]);
                                    ^
/in/foo.cc:161:31: error: 'sqrt' was not declared in this scope
 double s1=(-COEF[1]+sqrt(delta))/(2*COEF[2]),s2=(-COEF[1]-sqrt(delta))/(2*COEF[2]);
                               ^
/in/foo.cc:163:4: error: 's2' was not declared in this scope
 s1>s2?(s1=s1+s2,s2=s1-s2,s1=s1-s2):0;
    ^~
/in/foo.cc:165:30: error: 'printf' was not declared in this scope
 printf("2\n%.5f %.5f\n",s1,s2);
                              ^
/in/foo.cc:173:42: error: 'printf' was not declared in this scope
 printf("1\n%.5f\n",(-COEF[1])/(2*COEF[2]));
                                          ^
/in/foo.cc:181:13: error: 'printf' was not declared in this scope
 printf("0\n");
             ^