View Compilation Error

0_0_34396727_24805.cpp: In function 'int main()':
0_0_34396727_24805.cpp:11:24: error: 'strlen' was not declared in this scope
         len1 = strlen(a);
                        ^
0_0_34396727_24805.cpp:13:26: error: 'strchr' was not declared in this scope
         if (strchr(a, '.') != NULL)         //strchr函数功能为在一个串中查找对于给定字符的第一个匹配之处
                          ^
0_0_34396727_24805.cpp:20:26: error: 'strchr' was not declared in this scope
         if (strchr(b, '.') != NULL)
                          ^
0_0_34396727_24805.cpp:27:24: error: 'strcmp' was not declared in this scope
         if (strcmp(a, b) == 0)
                        ^