View Compilation Error

0_0_16180557_18790.cpp: In function 'void dfs(node*, char*, int)':
0_0_16180557_18790.cpp:66:18: error: 'strlen' was not declared in this scope
  if(v==strlen(str))
                  ^
0_0_16180557_18790.cpp:72:18: error: 'strcpy' was not declared in this scope
    strcpy(ans,sum);
                  ^
0_0_16180557_18790.cpp:78:30: error: 'strlen' was not declared in this scope
  int L=strlen(tel[str[v]-'2']);
                              ^
0_0_16180557_18790.cpp: In function 'int main()':
0_0_16180557_18790.cpp:122:14: error: 'strlen' was not declared in this scope
    L=strlen(p);
              ^
0_0_16180557_18790.cpp:127:15: error: 'strcpy' was not declared in this scope
     strcpy(q,p);
               ^