C ++中的字符串，字符比较

Question

*Hello! I'm making program where user enters a sentence and program prints out how many letters there are in a sentence(Capital and non-capital). I made a program but it prints out weird results.Please help as soon as possible. :)

include <iostream>
include <string>
using namespace std;

int main()
  {
string Sent;

 cout << "Enter a sentence !"<<endl;
 cin>>Sent;

    for(int a=0;a<Sent.length();a++){

        if (96<int(Sent[a])<123 || 64<int(Sent[a])<91){
           cout << "this is letter"<< endl;
        }else{
            cout << "this is not letter"<< endl;
        }

    }



}

Answer 1

First of all you will get one and only one word. cin >> Sent won't extract the whole line. You have to use getline in order to do this.

Second, you should use isspace or isalpha instead to check whether a character is whitespace/an alphanumeric symbol.

Third, a < b < c is essentially the same as (a < b) < c , which isn't what you meant ( a < b && b < c ) at all.

Answer 2

You can do the following with std::alpha:

#include <iostream>
#include <string>
#include <cctype> 
using namespace std;

int main()
{
   string Sent;

    cout << "Enter a sentence !"<<endl;
    //cin >> Sent;
    std::getline (std::cin,Sent);
    int count = 0;

     for(int a=0;a<Sent.length();a++){
        if (isalpha(Sent[a])
        {
          count ++;
         }
      }
      cout << "total number of chars " << count <<endl;

  }

It is better to use getline than using cin>> if your input contains whitespace.

Answer 3

if (96<int(Sent[a])<123 || 64<int(Sent[a])<91){

This is wrong.You can't compare using this notation. You must do:

if( Sent[a] > 96 && Sent[a] < 122 || ....

Answer 4

if (96 < Sent[a] && Sent[a]<123 || 64 < Sent[a] && Sent[a]<91)

This is what you want, because:

96<int(Sent[a])<123

Will evaluate 96<int(Sent[a]), as bool, then, will compare it (that is 0 or 1) with 123.

Answer 5

This line

if (96<int(Sent[a])<123 || 64<int(Sent[a])<91)

must be something like this

if ((96<int(Sent[a]) && int(Sent[a])<123) || (64<int(Sent[a]) && int(Sent[a])<91))

but I suggest using the function isalpha() defined in the cctype header file.