Help, im new to C++ i need some advice

#include <ios开发者_JS百科tream>
#include <string>
using namespace std;

int main()
{
  cout << "Input a Sentence: ";
  cin >> x;
  {
  char* string = x;
  int letter_count[26];

  // Initialization
  for(int i=0; i<26; letter_count[i++]=0);

  // Counting the number of letters
  for(int i = 0; string[i] != '\0'; i++) {
    if(string[i] > 64 && string[i] < 91)
      letter_count[string[i]-65]++;
    else if (string[i] > 96 && string[i] < 123)
      letter_count[string[i]-97]++;

    else if (string[i] == '.')
      break;
  }

  // Show the result

  for(int i=0; i < 26; i++)
    if (letter_count[i] != 0)
      std::cout << letter_count[i] << " "<< char(i+97) << std::endl;
  }
}

Why doesn't this program compile?

• Your code won't be able to compile. You used x in cin << x before declaring it.
• use std::getline to read a line.
• Don't use std type name (string) as the variable name. (Thanks to bdonlan)

• Don't use magical number (63,etc).

  By combine above together, we have this. This is far from perfect , but it is improved.

      cout << "Input a Sentence: ";
      string line;
      std::getline(std::cin , line);
  
  int letter_count[26];
  
  // Initialization
  for(int i= 0; i<26; i++)
  {
      letter_count[i] = 0;
  }
  
  // Counting the number of letters
  for(int i = 0; line[i] != '\0'; i++) {
      if(line[i] >= 'a' && line[i] <= 'z'){
              letter_count[line[i]-'a']++;
      }else if (line[i] >= 'A' && line[i] <= 'Z'){
              letter_count[line[i]-'A']++;
      }else if (line[i] == '.')
              break;
  }
  
  // Show the result
  

don't use the word string as your variable name, you are including the string.h header which defines a class with the same name,

and yes,it would be better if you write a question with a specific problem

You don't have declared the x variable. It should be a std::string:

string x;

After reading the input you declare a variable called string (with char* string = x;). If you leave out that line and just use x everywhere where you now use string your program compiles fine.

It also already very nearly does what I guess you intend it to do.

For starters you have to declare x before you can use it.

Also you can change

 int letter_count[26];

  // Initialization
  for(int i=0; i<26; letter_count[i++]=0);

to just

int letter_count[26] = {0};

The specific problem in your code is that you didn't declare the variable x before use. (And your declaration was weird. To declare a variable, put the type followed by the name, like char* x, optionally followed by an assignment to initialize it, char* x = "hello world". After the variable has been declared, the compiler will let you use it.

#include <iostream> // include the header containing cout and cin
#include <string> // include the header containing the string class
// using namespace std; // don't do this. Prefix standard library names with the std namespace instead

int main()
{
  std::cout << "Input a Sentence: ";
  std::string x; // declare a variable named x, so we can use it afterwards - and use the C++ string class, not char*
  //std::cin >> x; // only reads a word into x. If we want a sentence, use getline instead:
  std::getline(cin, x);
  int letter_count[26] = {}; // automatically fills the array with zeros

  // Counting the number of letters
  for(std::string::iterator it = x.begin(); it != x.end(); ++it) { // might as well use iterators. That's what they're for. And then your code behaves better if the string actually contains a \0 character.
    if(*it >= 'A' && *it <= 'Z'){ // never leave out the {}'s. It'll blow up on you later, when you modify the code
      letter_count[*it - 'A']++;
    }
    else if (*it >= 'a' && *it <= 'z'){
      letter_count[*it-'a']++;
    }
    else if (*it == '.'){
      break;
    }
  }

  // Show the result

  for(int i=0; i < 26; i++)
    if (letter_count[i] != 0)
      std::cout << letter_count[i] << " "<< static_cast<char>(i+97) << std::endl; // prefer C++-style casts
  }
}