Cannot get my getchar() function to work how I want it to work, output is10 not 2 c++

Question

I cannot figure out why my getchar() function is not working the way I want it to work. I am getting 10 not 2. Please take a look.

Main():

#include <cstdlib>
#include <iostream>
#include <fstream>

using namespace std;

int main() {
    int var, newvar;
    cout << "enter a number:" << endl;
    cin >> var;
    newvar = getchar();
    cout << newvar;

    return 0;
}

Here is my output:

enter a number:
220
10

Ultimately though I need to be able to distinguish between a '+' '-' or letter or number.

Looks like you captured the line feed left over from `cin >> var;`. — user4581301, Sep 25 '17 at 05:06
also, if you remove `cin >> var` you still won't get `2`, you'll get `50` — kmdreko, Sep 25 '17 at 05:10
Why are you using `getchar()` in a C++ program? Couldn't you just use `std::cin` for that as well? What are you trying to accomplish here? — user1118321, Sep 25 '17 at 05:14
And why are you *mixing* `stdio` with `streams`? Don't do that. — user207421, Sep 25 '17 at 05:17
I am doing an assignment for class and was told the best way was getchar() @user1118321 — Dustin177820, Sep 25 '17 at 05:42
`getchar` *is* working as documented. Compile with all warnings & debug info (`g++ -Wall -Wextra -g`) and use the `gdb` debugger to run your program step by step and find your bugs — Basile Starynkevitch, Sep 25 '17 at 06:37
@user443355566644: "*I am trying to scan an input one character at a time*" - use [`std::cin.get()`](http://en.cppreference.com/w/cpp/io/basic_istream/get) in C++, not `getchar()`. "*I am doing an assignment for class and was told the best way was getchar()*" - you were told wrong — Remy Lebeau, Sep 25 '17 at 15:30

Seltymar · Accepted Answer · 2017-09-25T07:35:07.480

1

This is maybe not the cleanest way to do it but you can get every char one by one :

#include <iostream>

using namespace std;

int main()
{
    int var;
    cout << "enter a number:" << endl;
    cin >> var;
    std::string str = to_string(var);
    for(int i=0; i < str.length();++i)
        cout << str.c_str()[i] << endl;
    return 0;
}

If you enter for example: "250e5" it will get only 250 and skip the last 5.

Edit: This is just a simple parser and does not do any logic. If you want to make a calculator I would recommend you to look at what Stroustrup did in his book the c++ programming language.

int main()
{
    string str;
    cout << "enter a number:" << endl;
    cin >> str;
    for(int i=0; i < str.length();++i) {
        char c = str.c_str()[i];
        if(c >= '0' && c <= '9') {
            int number = c - '0';
            cout << number << endl;
        }
        else if(c == '+') {
            // do what you want with +
            cout << "got a +" << endl;
        } else if(c == '-') 
        {
            // do what you want with -
            cout << "got a -" << endl;
        }
    }
    return 0;
}

edited Sep 25 '17 at 07:35

answered Sep 25 '17 at 06:29

Seltymar

337
6
21

Thank you this helps but it does not solve my problem. I need to be able to read '+' or '-' or 'a'-'z'. – Dustin177820 Sep 25 '17 at 07:02
@user443355566644 That's not clear what you want to achieve. From your comment, you want to get every character one by one. You should rewrite your question with more explanation at what you want to do. – Seltymar Sep 25 '17 at 07:22
This is exactly what I needed. Thank you! – Dustin177820 Sep 25 '17 at 18:35
@user443355566644 if this answer your question, accept it as an answer :). – Seltymar Sep 26 '17 at 07:03

Cannot get my getchar() function to work how I want it to work, output is10 not 2 c++

1 Answers1