View Compilation Error

0_0_13224655_12419.cpp: In function 'void change(char*)':
0_0_13224655_12419.cpp:9:18: error: 'strlen' was not declared in this scope
  len = strlen(str);
                  ^
0_0_13224655_12419.cpp:10:19: error: 'strstr' was not declared in this scope
  if(strstr(str,"."))  
                   ^
0_0_13224655_12419.cpp: In function 'int main(int, char**)':
0_0_13224655_12419.cpp:28:23: error: 'strcmp' was not declared in this scope
   if(!strcmp(str1,str2))  
                       ^