C++ - Function won't print first letter of line

Question

Can anyone tell me why my function won't print the first letter of names after the first one? This is my code.

void plusScores(ifstream& in, ostream& out)
{
    string name;
    char score;
    int plus = 0;
    int minus = 0;;
    double sum;
    double percent;

    while (getline(in, name))
    {

        while (in >> score && (score == '+' || score == '-'))
        {
            if (score == '+')
                plus++;
            else if (score == '-')
            minus++;
        }

        sum = plus + minus;
        percent = (plus / sum) * 100;

        out << fixed << showpoint << setprecision(1);

        out << name << ": " << percent << "% plus" << endl;

        plus = 0;
        minus = 0;  
    }
}

My output should look like this:

Kane, Erica: 40.0% plus
Chandler, Adam: 75.0% plus
Martin, Jake: 100.0% plus
Dillon, Amanda: 62.5% plus

Instead I get this:

Kane, Erica: 40.0% plus
handler, Adam: 75.0% plus
artin, Jake: 100.0% plus
illon, Amanda: 62.5% plus

The text file it's reading looks like this:

Kane, Erica
--+-+
Chandler, Adam
++-+
Martin, Jake
+++++++
Dillon, Amanda
++-++-+-

score 4 · Answer 1 · answered Apr 12 '17 at 06:04

When you get to the end of the line of "--+-+", your code has read in the first character of the name. It is no longer there for getline to read. This is because the in >> score skips whitespace characters.

You could use in >> std::noskipws >> score. However, this will probably lead to some interesting other issues in a real world application if there are spaces between the line of +- and the newline, you'll read an empty line of "name" and then use the name to calculate a zero score (unless there are + or - in the beginning of the name).

The other choice is to use getline consistently, and instead of reading a character at a time from the input file, read a line, and count + and - in the string you got.

A third choice would be to "unget" the last character from the input. After your loop, insert in.unget(score); to use this method.

All of these methods have slightly different pros and cons. In general, mixing getline and >> is not a great idea.

score 3 · Accepted Answer · edited May 23 '17 at 11:55

3

Because while (in >> score && (score == '+' || score == '-')) reads these letters. As they are not + or - they are not used then.

Instead, I recommend using getline for the +/- line as well, and then count the number of + and - in the complete string. (See this question for how to count them.)

edited May 23 '17 at 11:55

Community

1
1

answered Apr 12 '17 at 06:00

wkl

1,896
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[`std::count`](http://en.cppreference.com/w/cpp/algorithm/count) in conjunction with the recommended use of `std::getline` for the line of `+-` values would probably come in pretty handy. – WhozCraig Apr 12 '17 at 06:14

score 1 · Answer 3 · answered Apr 12 '17 at 06:09

Fix your code:

void plusScores(ifstream& in, ostream& out)
{
string name;
string scores;

int plus = 0;
int minus = 0;;
double sum;
double percent;

while (getline(in, name))
{

    getline(in, scores);
    int loc = 0;
    while (loc < scores.length())
    {
        if (scores.at(loc) == '+')
            plus++;
        else if (scores.at(loc) == '-')
            minus++;
        loc++;
    }

    sum = plus + minus;
    percent = (plus / sum) * 100;

    out << fixed << showpoint << setprecision(1);

    out << name << ": " << percent << "% plus" << endl;

    plus = 0;
    minus = 0;  
}
}

C++ - Function won't print first letter of line

3 Answers3