Thread: Stupid syntax error?

so to declare a long int in Borland C++ 5.5 I use the syntax 'long int <name>'? and is a short 'short int <name>'?

See, when you read in a value beyond the max value it wraps around.

It doesn't seem to be so with cin. If cin >> num fails, it seems to leave num as it is.

Code:

int num = 42;
cout << "Please don't enter a valid integer: ";
cin >> num;
cout << num; //prints 42

Anyway, here's what I would try:

Code:

#include <iostream>
#include <string>
#include <sstream>
enum {NOT_INTEGER = 0, OUT_OF_RANGE, OK};

int CheckRange(const std::string & a)
{    
    //If anybody knows a simpler way, please tell so!
    
    //test 1: is it fully convertible
    int num;
    std::stringstream test(a);
    if (test >> num && test.eof()) return OK;
    
    /*test 2a: minus sign should be at pos 0 if anywhere*/
    size_t pos = a.rfind('-');
    if (pos && pos != std::string::npos) return NOT_INTEGER;
    
    /*test 2b: if minus sign is at pos 0, string must be
    longer than 1 character*/
    if (pos == 0 && a.size() == 1) return NOT_INTEGER;
    
    /*test 3: find other non-digits*/
    if (a.find_first_not_of("-1234567890") == std::string::npos)
        return OUT_OF_RANGE;
    else
        return NOT_INTEGER;
}

int main()
{
    std::string s;
    while (1) {
        std::cout << "Enter an integer: ";
        std::cin >> s;
        switch (CheckRange(s)){
            case OK:
                std::cout << "That's a valid integer." << std::endl;
                break;
            case OUT_OF_RANGE:
                std::cout << "Numeric but out of range." << std::endl;
                break;
            case NOT_INTEGER:
                std::cout << "That's not an integer." << std::endl;
                break;
        }
    }
}

Okay great, I get it. I'll just stick with using a long int for the input and checking it against numeric_limits<int>. The program doesn't need to be totally foolproof and I've only been learning c++ for two days
Maybe I'll make it foolproof after I've worked on arrays and functions, thanks for the help!

Originally Posted by rickyoswaldiow

Okay great, I get it. I'll just stick with using a long int for the input and checking it against numeric_limits<int>. The program doesn't need to be totally foolproof and I've only been learning c++ for two days
Maybe I'll make it foolproof after I've worked on arrays and functions, thanks for the help!

If by a long int you mean long, be warned: very often it would be just as large as a regular int, and you'd gain nothing.

If you mean __int64 and your compiler accepts it: why bother to check if the input is in range of int? I mean, you'd still have to validate the input otherwise (the user might enter non-numbers anyway). But why would you be interested to restrict your user to 32 bits, if you can use and are using 64-bit integers?

You could just as easily demonstrate your understanding of checking ranges with other examples (e.g precentages as suggested above). It might also be more practical to learn what to do if user enters "fourty-two" where an int is expected.