View Compilation Error

0_0_20014606_25379.cpp: In function 'int main()':
0_0_20014606_25379.cpp:52:24: error: 'strlen' was not declared in this scope
         len1=strlen(s+1);
                        ^
0_0_20014606_25379.cpp:62:47: error: 'strcmp' was not declared in this scope
             if(t<ans||t==ans&&strcmp(p+1,str+1)<0)
                                               ^
0_0_20014606_25379.cpp:65:33: error: 'strcpy' was not declared in this scope
                 strcpy(str+1,p+1);
                                 ^