How do I detect if the user enter a number only or number and words?

[rimun]

I got an assignment where it's optional requirements require me to convert x(real number) from degree to radian if the user's input has the word 'degree' appended at the end(example: sin 30 degree will be automatically converted to sin 0.523599). If the word 'degree' is absent from the input, no conversion is required.

How can i do this in C++

I had tried this way:

#define PI 3.14159265
string check;

If(check.empty())
number = number;
Else if(!check.empty && check == "degree")
number = number*PI/180;

Then using some calculation coding the program will display the answer appropriately (example coding: sin (number);)

But these way doesn't seem to works as intended.
How should i do it?

[Golden Lizard]

<cctype> provides functions for this sort of thing.
http://www.cplusplus.com/reference/cctype/

Just save the input in a string, then parse it. Use std::string::find to check if the word degree is present.

[JLBorges]

#include <iostream>
#include <string>
#include <cctype>
#include <cmath>

int main()
{
    std::string fn_name ;
    double number ;

    if( std::cin >> fn_name && std::cin >> number )
    {
        // skip characters in the input buffer till a new line
        // or a non-white-space character is extracted
        char c ;
        while( std::cin.get(c) && c != '\n' && std::isspace(c) ) ;

        if( c != '\n' ) // if it is not a new line
        {
            // put the non-white-space character back into the input buffer
            std::cin.putback(c) ;

            // read it in as a string
            std::string deg ;
            std::cin >> deg ;
            if( deg == "degrees" )
            {
                // convert number from degrees to radians
                static constexpr double pi = 3.1415926535897932385 ;
                std::cout << number << " degrees == " ;
                number *= pi / 180 ;
                std::cout << number << " radians\n" ;
            }
        }

        std::cout << fn_name << '(' << number << ") == " ;
        if( fn_name == "sin" ) std::cout << std::sin(number) << '\n' ;
        // etc
    }
}

http://coliru.stacked-crooked.com/a/ba77e10cb56d623f

[Chervil]

Or read the entire input as a single string. Then use a stringstream to parse it.

    string input;
    cout << "Enter your input:\n";
    getline(cin, input);
    
    string name, units;
    double value;
    
    istringstream ss(input);
    
    if (ss >> name >> value)
    {
        if (ss >> units && units == "degree")
        {
            value = value * PI / 180.0;    
        }    
        
        if (name == "sin")
            cout << sin(value) << '\n';
    } 

(requires #include <sstream> to use stringstream).

[lastchance]

#include <iostream>
#include <cmath>
#include <map>
#include <string>
using namespace std;

int main()
{
   constexpr double DEGTORAD = 3.14159265359 / 180;
   string func, rest;
   double angle;
   map<string,double(*)(double)> op = { { "sin", sin }, { "cos", cos }, { "tan", tan } };
   cout << "Input trig function and angle: ";
   cin >> func >> angle;
   getline( cin, rest );   if ( rest.find( "degree" ) != string::npos ) angle *= DEGTORAD;
   cout << op[func]( angle );
}

Input trig function and angle: sin 30 degree
0.5

Input trig function and angle: tan 135 degree
-1 

Input trig function and angle: cos 3.14159265
-1

[Chervil]

What if the user enters something like sin 30 radian degree?