error in my function

[miller18]

Hi I am relatively new beginner. I am trying to write a function that outputs the first and last digits of a number and also the total number digits of a number(the number is inputted by the user). The program works on its own, but when I try to make it a function it compiles and then I get a really weird error.

This is what I have written as my function:


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

void order(string str)
{ int d =0;
int e;
string f;
string l;
for (d; d<str.length(); d++)
{string ch= str.substr(d,1);
string f = str.substr(0,1);
e = d-1;
string l = str.substr(e,1);
}
cout << "The first digit is "<< f << ". The last digit is "<< l << ".
The total number of digits is "<< d<< endl;

}

int main()
{ int d; //total number of digits
string str;
cout << "Please enter a number." << endl;
cin >> str;

order(str);

return 0;
}

And the error message I get when I input a number is:

terminate called after throwing an instance of 'std::out_of_range'
what(): basic_string::substr
Aborted

If anyone can help me correct the error that would be great!

[Fransje]

It gave me very strange errors too, so here is the corrected, working version:

#include <iostream>
#include <string>

using namespace std;

void Order( string str ) { 
    cout << "The first digit is " << str[ 0 ] << endl;
    cout << "The last digit is " << str[ str.length() - 1 ] << endl;
    
    int totalNumber = 0;
    string subString = "";
    
    for ( int i = 0; i < str.length(); i++ ) {
        subString = str.substr( i, 1 );
        
        totalNumber += atoi( subString.c_str() );
    }
    
    cout << "The total number of digits is " << totalNumber << endl;
}

int main( int argc, char* argv[] ){     
    string str;
    
    cout << "Please enter a number: ";
    cin >> str;

    Order( str );
    
    cin.get();
    cin.get();

    return 0;
}

[Chervil]

Code tags and indentation would make the code more legible.

void order(string str)
{ 
    int d =0;
    int e;
    string f;
    string l;

    for (d; d<str.length(); d++)
    {
        string ch= str.substr(d,1);
        string f = str.substr(0,1);
        e = d-1;
        string l = str.substr(e,1);
    }
    cout << "The first digit is "<< f << ". The last digit is "<< l 
        << ". The total number of digits is "<< d<< endl;

}

On line 12, d is 0, e is -1 and so you have: str.substr(-1,1); which is not good :)

Do you actually need a for loop?

[Stewbond]

I think your function can be simplified:

void order(string str)
{ 
  if (str.length() < 1) return; // protect against invalid memory access.
  cout << "The first digit is "              << str.at(0);
  cout << ". The last digit is "             << str.at( str.length() - 1 );
  cout << ". The total number of digits is " << str.length() << endl;
}

[Fransje]

oh wait, I thought total number was the sum of all the digits in the number :)