Delay time calculator input problems

[MrDinsdale]

Hi,

Im new to C++ but we have been doing a module on it at uni. We had to create a simple reverb time calculator, to anyone not familiar it just works out different note durrations ie 1/4 or 1/16 notes at a different tempos in milliseconds.

The problem is that when the user enters a BPM value which is not a number it causes the program to loop infinately, i know its due to using a double data type to store the BPM but just wondered if there is a way around it or alternative.

Any help would be great, our lecturer said it wasnt vital that this was corrected but would gain marks by resolving it.

Cheers

[Jeff HS]

Hi,
Use a temporary string variable to store the user input and atof to convert it back to double:

//---------------< Simple compatible delay time calculator >--------------------
#include <iostream>
#include <iomanip>
#include <cstdlib>
using namespace std;

//-------------------< Declare variables and functions >------------------------

double rt4; //Return value for 1/4 note time duration
double bpm; // Beats per minute
int const mseconds = 60000; // ms in a minute
char repeatValidation; // Choice for repeating application
char quit;

// Function to calculate time duration for quater notes
double rtCalc(double beatPM){
	double r; // Value to return
	r = (mseconds/beatPM);
	return (r);
}



//-------------------------< Main Program Function >-----------------------------


int main(){
	
	
do{
		for(;;){
		
                char userInput[20]; // string from <string> highly recommended but i am not sure if you are allowed to use it.

		cout << "Please enter your tempo for a list of suitable delay times: (between 1 and 500 bpm)\n\n\tTempo = ";
                cin.sync(); // discards any trash characters in the stream
		cin >> setw(20) >> userInput; // setw(20)makes sure cin only reads 20 characters and 
//reserves the last one for '\0' (null). Not necessary with string from <string>.
	        
         	bpm = atof(userInput);
		
               		
			if (bpm >= 1 && bpm <= 500){
                                 //you should inform the user what was his input. just a suggestion though
			        cout << "Ok the results for: "<< bpm << " is: " << endl;
				rt4 = rtCalc(bpm);

				double rt2 = rt4*2; //Return value for 1/2 note time duration
				double rt8 = rt4/2; //Return value for 1/8 note time duration
				double rt16 = rt4/4; //Return value for 1/16 note time duration
				double rt32 = rt4/8; //Return value for 1/32 note time duration

				// results from calculations displayed formatted:

				cout << "\n\nNote Duration\t\tTime in ms";
				
				cout << setprecision(2);//sets precision of output to 2 dp
				cout << fixed;// sets results to display with fixed point
	
				cout << "\n1/2 note\t\t" << rt2 << endl;
				cout << "Dotted 1/2 note\t\t" << rt2*1.5 << endl;
			
				cout << "\n\n1/4 note\t\t" << rt4 << endl;
				cout << "Dotted 1/4 note\t\t" << rt4*1.5 << endl;
		
				cout << "\n1/8 note\t\t" << rt8 << endl;
				cout << "Dotted 1/8 note\t\t" << rt8*1.5 << endl;

				cout << "\n1/16 note\t\t" << rt16 << endl;
				cout << "Dotted 1/4 note\t\t" << rt16*1.5 << endl;
	
				cout << "\n1/32 note\t\t"<< rt32 << endl;
				cout << "Dotted 1/32 note\t" << rt32*1.5 << endl;

				break;
			}

			else{
				cout << "\nThat was not a valid tempo.\n\n";
			}
		}
                for(;;){
			cout << "\n\n\nDo you wish to repeat? (y for yes or n for no): ";
			cin >> repeatValidation;
	
			if (repeatValidation == 'y'||repeatValidation == 'Y'){
				cout << "\n\n\n";// loops back to start
				break;
			}
			else if (repeatValidation == 'n'||repeatValidation == 'N'){
				quit = 'y';// Quits for loop and changes the value of the quit var to y to terminate the app.
				break;
			}
			else{
				cout << "\n\nThat was not a valid reply.";
			}
		}
	}while(quit != 'y');
}

dont forget to

#include <cstdlib> 

Note: atof returns 0 if it fails to convert but since your program does not accept 0 it will output

cout << "\nThat was not a valid tempo.\n\n";

http://www.cplusplus.com/reference/clibrary/cstdlib/atof.html

Jeff

[MrDinsdale]

Great,

Thats so helpful, im not familiar with the cstdlib but ill have a look into it.

I assumed that the answer would be with strings however I was not sure where to start.

Oh and we can use the #include <string> so if i add that do i not have to worry about the setw(256) bit?

Thanks again,

[MrDinsdale]

Sorry to be a pain but how would you write it using the <string>?

Ive tried what I thought it would be but gives the errors:

error C2664: 'atof' : cannot convert parameter 1 from 'std::string' to 'const char *'

Cheers

[Jeff HS]

Oh it's not a problem i am stuck in my office waiting for a response from a client so all i am doing is surfing the internet and helping people here.

If userInput was of string type:

bmp = atof(userInput.c_str());

Yeah like i said in the comments it is not necessary with string class, so just delete that.

http://www.cplusplus.com/reference/string/string/c_str.html
http://www.cplusplus.com/reference/string/string/


Jeff

[MrDinsdale]

thanks for the advice, ive managed to find my own way round it using your info! thanks again.