View Compilation Error

0_0_16609912_20438.cpp: In function 'int main()':
0_0_16609912_20438.cpp:4:16: error: 'str' was not declared in this scope
     while(gets(str)!=NULL)
                ^
0_0_16609912_20438.cpp:4:19: error: 'gets' was not declared in this scope
     while(gets(str)!=NULL)
                   ^
0_0_16609912_20438.cpp:4:22: error: 'NULL' was not declared in this scope
     while(gets(str)!=NULL)
                      ^
0_0_16609912_20438.cpp:6:29: error: 'memset' was not declared in this scope
         memset(a,0,sizeof(a));
                             ^
0_0_16609912_20438.cpp:7:23: error: 'strlen' was not declared in this scope
         len=strlen(str);
                       ^
0_0_16609912_20438.cpp:15:48: error: 'printf' was not declared in this scope
             printf("%c:%d\n",(char)(i+'a'),a[i]);
                                                ^
0_0_16609912_20438.cpp:17:20: error: 'printf' was not declared in this scope
         printf("\n");
                    ^