Converting a char to double?

[stu74uk]

I've written a calculator program but at the moment I'm not getting the right calculation results. I want the program to convert the character input into a double data type.

I tried using the function atof but this didn't work. does anyone have any solutions?

double add(double x, double y)
{
return x + y;
}

double subtract(double x, double y)
{
return x - y;
}

double divide(double x, double y)
{
return x / y;
}

double multiply(double x, double y)
{
return x * y;
}


int main()
{
char first_input;
char second_input;
double x;
double y;
char op;
bool valid = true;

cout << &quot;*****************************&quot; << endl;
cout << &quot;** calculator **&quot; << endl;
cout << &quot;*****************************&quot; << endl;

do
{
cout << &quot;Please enter a number: &quot;;
cin >> first_input;
x = atof(first_input);

valid = (x >= '0' && x <= '9');
if(valid)
cout << &quot;Correct data!\n&quot;;
else
cout << &quot;In-correct data\n&quot;;
}while(!valid);

 

[palbano]

>> char first_input;
>> cin >> first_input;
>> x = atof(first_input);

Don't you need more than a single character to read in a number greater than 9?

-pete

 

[BoulderBum]

x is declared as a double but you are comparing it to character values ( x >= '0'... ). Try having a character value compared ( first_input >= '0' && first_input <= '9' ) then converting it to double only if the condition is true.

 

[BoulderBum]

Also, you should set variable &quot;valid&quot; to true or false in the proper places in your pair of if statements.

 

[BoulderBum]

Also, you should set variable &quot;valid&quot; to true or false in the proper places of your if/else statement.

 

[pankajkumar]

Use _ecvt/_fcvt/_gcvt for double to char
and strtod, wcstod for char to double
You can chage the code accodrdingly
hope it helps
Let me know

 

[rossno]

This is NOT elegant, but might help a little:


// cin_test.cpp : Defines the entry point for the console application.
//

#include &quot;stdafx.h&quot;
#include <iostream.h>
#include <iomanip.h>
#include <ctype.h>
#include <stdlib.h>
#include <conio.h>

// I've written a calculator program but at the moment I'm not getting the right calculation results. I want the program to convert the character input into a double data type.

//I tried using the function atof but this didn't work. does anyone have any solutions?

double add(double x, double y) { return x + y;}

double subtract(double x, double y) { return x - y;}

double divide(double x, double y) { return x / y;}

double multiply(double x, double y) { return x * y;}


// -----------------------------------
int main(int argc, char* argv[])
{

double x, y;

cout << &quot;*****************************&quot; << endl;
cout << &quot;** my calculator **&quot; << endl;
cout << &quot;*****************************&quot; << endl;

// setup so U can input into a fixed fld. including decimals.
cout << setiosflags(ios::fixed); // or ios::floatfield) ;

FOOBAR:
try
{
cout << &quot;Please enter first number: &quot;;
cin >> x;

cout << &quot;Please enter second number: &quot;;
cin >> y;
}
catch (...) // catch all errors. Need more robust err checking.
{
cerr << &quot;fixed number input err. Rethink and try again.&quot; << endl;
goto FOOBAR;
}

cout <<&quot;x = &quot; << x << endl;
cout <<&quot;y = &quot; << y << endl;

cout << &quot;add x + y :&quot; << add (x, y) << endl;
cout << &quot;subtract x - y :&quot; << subtract(x, y) << endl;
cout << &quot;multiply x * y :&quot; << multiply(x, y) << endl;
cout << &quot;divide x / y :&quot; << divide (x, y) << endl;

cout << &quot;---------------- all done --------&quot; << endl;

cout << &quot;Please enter first number: &quot; << endl;

char ch_x[7] = &quot;abcdef&quot; , *junk;
char ch_y[7] = &quot;ghijkl&quot; ;

cin >> ch_x;
x = strtod( ch_x, &junk ); // junk is stuff following legal digits.

cout << &quot;first_num: &quot; << x << &quot; - &quot; << junk <<endl;

cout << &quot;Please enter second number: &quot; << endl;

cin >> ch_y;
y = strtod( ch_y, &junk ); // junk is stuff following legal digits.

cout << &quot;second_num: &quot; << y << &quot; - &quot; << junk << endl;

cout << &quot;add x + y :&quot; << add (x, y) << endl;
cout << &quot;subtract x - y :&quot; << subtract(x, y) << endl;
cout << &quot;multiply x * y :&quot; << multiply(x, y) << endl;
cout << &quot;divide x / y :&quot; << divide (x, y) << endl;

cout << &quot;---------------- all done again --------&quot; << endl;

getch(); // dummy get. .. wait to see results.


return 0;
}

//~~~~~~~~~~~~~~~~~~~~ good luck

 

[stu74uk]

Cheers for all your help, the atof function did end up working it just needed the '&' operator to return the address of the variable.

~Stu.