View Compilation Error

0_0_13795649_21922.cpp: In function 'void set()':
0_0_13795649_21922.cpp:13:21: error: 'strcpy' was not declared in this scope
     strcpy(ch[0], "");  
                     ^
0_0_13795649_21922.cpp: In function 'void dfs(std::string, int, int)':
0_0_13795649_21922.cpp:38:23: error: 'strlen' was not declared in this scope
   int len=strlen(ch[k]);
                       ^
0_0_13795649_21922.cpp: In function 'int main()':
0_0_13795649_21922.cpp:78:24: error: 'strlen' was not declared in this scope
    for(i=0;i<strlen(str)-1;i++)
                        ^