View Compilation Error

0_0_20216643_23091.cpp: In function 'void insert()':
0_0_20216643_23091.cpp:14:17: error: 'strlen' was not declared in this scope
  len=strlen(ch+1);int x=0;
                 ^
0_0_20216643_23091.cpp: In function 'void AC()':
0_0_20216643_23091.cpp:32:3: error: expected ';' before '}' token
   }
   ^
0_0_20216643_23091.cpp: In function 'int main()':
0_0_20216643_23091.cpp:43:29: error: 'strlen' was not declared in this scope
   scanf("%s",s+1);n=strlen(s);
                             ^