a bug in a small exercise program.how do i correct it. thank you.

[JoeNapoleon]

/* exercise5-8.c -- convert fahrenheit temperature to celsius and kelvin temperature */


#include <stdio.h>
void Temperatures(double f);
const float ct1 = 1.8;
const float ct2 = 32.0;
const float ct3 = 273.16;
int main(void)
{
double temp;
printf("enter a temperature: ");
scanf("%lf", &temp);
while(temp >= 0 || temp < 0 ) // there is a bug
{
Temperatures(temp);
printf("enter a temperature(q to quit): ");
scanf("%lf", &temp);
}
printf("bye.\n");
return 0;
}

void Temperatures(double f)
{
double cel, kel;
cel = ct1 * f + ct2;
kel = cel + ct3;
printf("Fahrenheit temperature: %.2f, Celsius temperature: %.2f, \
Kelvin temperature: %.2f\n", f, cel, kel);
}


/* i need to input a number, if it is a character, then quit. but there is a bug in this program, when i input a char, it did not result correctly. how to write code in while condition? thank you. */

[ikamusume]

From man scanf

       These  functions  return  the  number  of input items successfully
       matched and assigned, which can be fewer  than  provided  for,  or
       even zero in the event of an early matching failure.

So you could check if scanf returns 1 do the conversion, else just quit.