(c++) problem in printing words of char array string - c++

Question

I'm making a c++ program using string(data type) and char array. Now, the data type is printing words alright. But, I'm having some trouble with the char array. Here's the code:
#include<iostream>
#include<string.h>
using namespace std;
int main(){
char str[200];
string str1;
cout<<"Enter a string:\t";
getline(cin,str1);
cout<<str1 <<endl;
cout<<"enter second string:\t";
cin>>str;
cin.get(str,200);
cout<<str;
}
code output
As, you can see in the output, the data type string is printing the words fine. But, the char array is missing the first word. Am I doing something wrong? or does the char array work in different way? Please explain. Thanks.

Answer 1

While you have already discovered that cin >> str; isn't required as you are simply writing again to str with cin.getline (str, sizeof str), there are a number of additional issues you should address:
1. Unless your compiler is ancient, you should #include <string>, not the C-header string.h;
2. Don't use magic-numbers in your code. If you need a constant, e.g. for the maximum number of characters in str, #define a constant or use a global enum to do the same, e.g.
#define MAXC 200 /* if you need a constant, #define one (or more) */
...
char str[MAXC]; /* don't use 'magic-number', use a constant */
That way when, and if you change the number of characters in str in the future, you don't have to pick through your entire code and change every occurrence of the magic-number, e.g. cin.get(str,200);.
3. Validate EVERY user input. Otherwise a failed input can set an error-bit on your input stream and additional attempts to read from a stream with an error-bit set can result in undefined behavior. You could do:
if (!getline(cin,str1)) { /* VALIDATE every input */
cerr << "error: input failure - str1.\n";
return 1;
}
and
if (cin.get (str, sizeof str))
cout << str << endl;
(note: there are no further attempted reads after cin.get (str, sizeof str) so guarding your use of str is sufficient)
4. Always output a newline after your final line output to ensure your program is POSIX compliant. Otherwise on many OS's you will mess up the users prompt if writing to stdout or you will create a non-POSIX compliant output file if redirecting the output to a file, e.g.
my cat has none01:22 wizard:~/dev/src-cpp/tmp/debug>
Putting it altogether, you could do something like:
#include <iostream>
#include <string> /* depending on your compiler */
#define MAXC 200 /* if you need a constant, #define one (or more) */
using namespace std;
int main (void) {
char str[MAXC]; /* don't use 'magic-number', use a constant */
string str1;
cout << "enter a string: ";
if (!getline(cin,str1)) { /* VALIDATE every input */
cerr << "error: input failure - str1.\n";
return 1;
}
cout << str1 << endl;
cout << "enter second string: ";
// cin >> str; /* not needed */
if (cin.get (str, sizeof str))
cout << str << endl;
}
Example Use/Output
$ ./bin/cin.get_getline
enter a string: my dog has fleas
my dog has fleas
enter second string: my cat has none
my cat has none

Answer 2

cout<<"enter second string:\t";
cin>>str;
cin.get(str,200);
here first you are trying to read the second word twice into same variable. comment one of them and try to print the content of str.
#include<iostream>
#include<string.h>
using namespace std;
int main(){
char str[200];
string str1;
cout<<"Enter a string:\t";
getline(cin,str1);
cout<<str1 <<endl;
cout<<"enter second string:\t";
// cin>>str;
cin.get(str,200);
cout<<str<<endl;
}