View Compilation Error

0_0_19218980_7733.cpp: In function 'int main()':
0_0_19218980_7733.cpp:18:28: error: 'strcmp' was not declared in this scope
     if(strcmp(ch[j],ch[j+1])>0) 
                            ^
0_0_19218980_7733.cpp:20:20: error: 'strcpy' was not declared in this scope
      strcpy(c,ch[j]);
                    ^
0_0_19218980_7733.cpp:29:26: error: 'strcmp' was not declared in this scope
   if(strcmp(ch[i],ch[i+1])==0)
                          ^