read values from a txt file

i know this a very baxic question but i don't have anyone to ask so please take pity on me!

i need to read in a list of numbers from a text file and save them to various variables. my problem isn't in reading the actual numbers in but that i don't know how to make an array of individual numbers represented by characters as one number.
for exp:

char b[]={ 1 , . , 5 , 3 }

but how do i get

double n=1.53

???

or am i going about this all wrong?

Well, I hope I understand your question...it looks to me like you want to read in numbers as represented in a text file and assign them to variables of type double instead of string or char*. The best way I knwo of to do this is to use a file stream, which you can then read from just like cin:

Code:

---

#include <iostream>
#include <fstream>

int main() {
    ifstream inFile("numbers.txt");
    double a, b, c;
    inFile >> a >> b >> c;
}

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If I am misinterpreting your question, please post again with more details.

Quote:

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char b[]={ 1 , . , 5 , 3 }

but how do i get

double n=1.53;

---

Okay, I know of no standard function to convert strings to doubles. If you know the values won't be floating point, you can use atoi() to convert the string to a number. For example:

char b[] = {"1234"};
int a = atoi(b);

Edit:: There's also atof() which converts a string into a floating point value. While you won't be getting the extra precision of a double, you can still extract the value from the string. Example:

char b[] = {"1.345"}
float a = atof(b);

You can use stringstreams to convert from any type to anytype as long as the stream output from one type is readable as stream input from the other type.

Code:

---

#include <sstream>
#include <iostream>

// generalized notion of stream_casting
template <class outType, class inType>
outType stream_cast(const inType& in)
{
        outType out;
        std::ostringstream outStream;
        outStream << in;
        std::istringstream inStream(outStream.str());
        inStream >> out;
        return out;
}


int main() {
        // specific example of stream casting
        char numAsChar[]="1.532";
        double numAsDouble;
        std::ostringstream out;

        out << numAsChar;
        std::istringstream in(out.str());

        in >> numAsDouble;

        std::cout << numAsDouble << std::endl;

        // use templated general stream cast
        numAsDouble = stream_cast<double>(numAsChar);

        std::cout << numAsDouble << std::endl;

        return 0;
}

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thank you so much to all of you that answered!