C++: error in reading character input using fgets()

Question

I have tried a simple code for using fgets(), as gets() is no more used and don't know anything better to read character input from keyboard. My code:

#include<iostream>
#include<cstdio>

using namespace std;



int main()
{
char a;
fgets(a, 100, stdin);
cout<<a;
return 0;
}

I got this error:

cpp:13:20: error: invalid conversion from 'char' to 'char*' [-fpermissive]
 fgets(a, 100, stdin);
                    ^
In file included from /usr/include/c++/7.2.0/cstdio:42:0,
                 from /usr/include/c++/7.2.0/ext/string_conversions.h:43,
                 from /usr/include/c++/7.2.0/bits/basic_string.h:6159,
                 from /usr/include/c++/7.2.0/string:52,
                 from /usr/include/c++/7.2.0/bits/locale_classes.h:40,
                 from /usr/include/c++/7.2.0/bits/ios_base.h:41,
                 from /usr/include/c++/7.2.0/ios:42,
                 from /usr/include/c++/7.2.0/ostream:38,
                 from /usr/include/c++/7.2.0/iostream:39,
                 from jdoodle.cpp:1:
/usr/include/stdio.h:564:14: note:   initializing argument 1 of 'char* fgets(char*, int, FILE*)'
 extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)
              ^~~~~

Then, I have tried

#include<iostream>    
#include<cstdio>

using namespace std;



int main()
{
char *a;
fgets(a, 100, stdin);
cout<<a;
return 0;
}

But incurred another error.

It will be appreciated if anyone shows a better method other than using fgets() or solve the above matter.

Answer 1

You are using char *fgets(char *str, int n, FILE *stream) wrong. It is intended to read multiple characters from file, actually up to n-1 characters, and the last character would be null terminator.

You could use int getc(FILE *stream) to read single character like:

int a;
if((a = getc(stdin)) != EOF) {
  // use a 
  char c = a; // convert to char explicitly
}

As you are using c++ an even better way is to use cin stream:

char a;
// formatted read(skips whitespace)
cin >> a;

// non-formated read
a = cin.get();

and don't forget to check if the operation has been successful after each read:

if(cin) {
  // success -> stream is ok
} else {
  // handle read error
}

If you want to read multiple characters:

#include <iostream>
#include <cstdio>

using namespace std;

int main() {
  char a[100]; // allocate static buffer
  fgets(a, 100, stdin); // read in the buffer
  cout << a;
  return 0;
}

Also the c++ way is:

#include <iostream>
#include <string>

using namespace std;

int main() {
  string s; // string that automatically manages memory
  cin >> s; // reads non-whitespace sequence of characters
  cout << s;
  return 0;
}

The other option is to read one line of characters, up to \n including whitespace.

#include <iostream>
#include <string>

using namespace std;

int main () {
  string s;

  getline(cin, s);
  cout << s;

  return 0;
}