Programming Forums > Application Development > C

gj15987 · Jun 17th, 2008, 5:45 AM

I'm using the following code to convert from Celcius to Fahrenheit but for some reason the actual conversion wont work and I can't work out why. The key lines are lines 13 and 16.

Basically, the first line tries fahrenheit = ((9 / 5) * celcius) + 32; however it's not performing the multiplication, it just adds 32 to celcius. I've tried changing it to 1.8 * celcius too but it still doesn't perform the multiplication.

If anyone can figure out why then I'd be grateful. Could it just be a problem with my machine? I'm using an Intel Mac running Leopard.

Thanks.

 c Syntax (Toggle Plain Text) 
int main()
{
    float celcius;   /* Declare only */
    float fahrenheit = 0; /* Declare and initialise */
 
    printf("Enter the temperature in degrees celcius: ");
 
    /* Read a value from the user and store it in celcius. */
    scanf("%f", &celcius);
 
    /* Perform the conversion. */
        // This one wont work
	fahrenheit = ((9 / 5) * celcius) + 32;
 
        // But this one does
	//fahrenheit = ((9 * celcius) / 5) + 32;
 
    printf("Temperature is \t%f 'C\n and \t\t%f 'F\n", celcius, fahrenheit);
 
    return 0;
}
int main()
{
    float celcius;   /* Declare only */
    float fahrenheit = 0; /* Declare and initialise */

    printf("Enter the temperature in degrees celcius: ");

    /* Read a value from the user and store it in celcius. */
    scanf("%f", &celcius);

    /* Perform the conversion. */
        // This one wont work
	fahrenheit = ((9 / 5) * celcius) + 32;

        // But this one does
	//fahrenheit = ((9 * celcius) / 5) + 32;

    printf("Temperature is \t%f 'C\n and \t\t%f 'F\n", celcius, fahrenheit);

    return 0;
}

Adak · Jun 17th, 2008, 6:31 AM

Your program is working, but integer 9 divided by integer 5 = 1, (the remainder is truncated), so it's not what you want.

Try (9.0 / 5.0) and see if your compiler won't accept them as floats, that way. Otherwise you may need to explicitly cast them to floats first, and then divide.

The second line of code works, because when 9 is multiplied by celcius, the 9 is being automatically re-cast to a float, since celcius is a float, already.

gj15987 · Jun 17th, 2008, 6:45 AM

Yes! Using 9.0 and 5.0 works!

Thanks a lot!

grumpy · Jun 17th, 2008, 8:01 AM

Quote:

Originally Posted by Adak

Try (9.0 / 5.0) and see if your compiler won't accept them as floats, that way. Otherwise you may need to explicitly cast them to floats first, and then divide.

A conversion/cast is not required. Simply use 9.0f/5.0f (or 1.80f) to have literals that are of type float.

BstrucT · Jun 17th, 2008, 8:33 AM

BstrucT · Jun 17th, 2008, 9:19 AM

A bit off topic, but you could use a function to do the work
in the program if you want.

Identify the formula, in this case it could be:

Farenheit = Celcius X 1.8 + 32. (I think)

Your function could look like this...

(Toggle Plain Text)

float convert( float a )
{
     float temp_farenheit = ( (temp_celcius * 1.8) + 32 );

     return (0);
}

Let the user enter the temp in Celcius, then pass that float value as an argument to the function above, then display the 'converted' result on - screen...
(%.2f will display to two decimal places, %.3f to three, etc.)

(Toggle Plain Text)

printf("Temperature in Celcius = %.2f ", temp_celcius
printf("Temperature in Farenheit = %.2f ", convert( temp_celcius );

>BstrucT

BstrucT · Jun 18th, 2008, 12:51 AM

Quote:

Originally Posted by BstrucT

Your function could look like this...

(Toggle Plain Text)

float convert( float a )
{
     float temp_farenheit = ( (temp_celcius * 1.8) + 32 );

     return (0);
}

Sorry guys, I was being dumb again, the function shouldn't return 0

, it
should obviously return temp_farenheit in above example.

My apologies.

Jun 17th, 2008, 5:45 AM	#1
gj15987 Programmer Join Date: Feb 2005 Posts: 47 Rep Power: 0	Converting Temperatures I'm using the following code to convert from Celcius to Fahrenheit but for some reason the actual conversion wont work and I can't work out why. The key lines are lines 13 and 16. Basically, the first line tries fahrenheit = ((9 / 5) * celcius) + 32; however it's not performing the multiplication, it just adds 32 to celcius. I've tried changing it to 1.8 * celcius too but it still doesn't perform the multiplication. If anyone can figure out why then I'd be grateful. Could it just be a problem with my machine? I'm using an Intel Mac running Leopard. Thanks. c Syntax (Toggle Plain Text) int main() { float celcius; /* Declare only / float fahrenheit = 0; / Declare and initialise / printf("Enter the temperature in degrees celcius: "); / Read a value from the user and store it in celcius. / scanf("%f", &celcius); / Perform the conversion. / // This one wont work fahrenheit = ((9 / 5) celcius) + 32; // But this one does //fahrenheit = ((9 * celcius) / 5) + 32; printf("Temperature is \t%f 'C\n and \t\t%f 'F\n", celcius, fahrenheit); return 0; } int main() { float celcius; /* Declare only / float fahrenheit = 0; / Declare and initialise / printf("Enter the temperature in degrees celcius: "); / Read a value from the user and store it in celcius. / scanf("%f", &celcius); / Perform the conversion. / // This one wont work fahrenheit = ((9 / 5) celcius) + 32; // But this one does //fahrenheit = ((9 * celcius) / 5) + 32; printf("Temperature is \t%f 'C\n and \t\t%f 'F\n", celcius, fahrenheit); return 0; }

Jun 17th, 2008, 6:31 AM	#2
Adak Hobby Coder Join Date: May 2006 Posts: 58 Rep Power: 0	Re: Converting Temperatures Your program is working, but integer 9 divided by integer 5 = 1, (the remainder is truncated), so it's not what you want. Try (9.0 / 5.0) and see if your compiler won't accept them as floats, that way. Otherwise you may need to explicitly cast them to floats first, and then divide. The second line of code works, because when 9 is multiplied by celcius, the 9 is being automatically re-cast to a float, since celcius is a float, already.

Jun 17th, 2008, 6:45 AM	#3
gj15987 Programmer Join Date: Feb 2005 Posts: 47 Rep Power: 0	Re: Converting Temperatures Yes! Using 9.0 and 5.0 works! Thanks a lot!

Jun 17th, 2008, 8:33 AM	#5
BstrucT Hobbyist Programmer Join Date: Dec 2007 Location: Durban, South-Africa Posts: 198 Rep Power: 1	Re: Converting Temperatures Cool __________________ Be kinder than necessary because everyone you meet is fighting some kind of battle.

Jun 17th, 2008, 9:19 AM	#6
BstrucT Hobbyist Programmer Join Date: Dec 2007 Location: Durban, South-Africa Posts: 198 Rep Power: 1	Re: Converting Temperatures A bit off topic, but you could use a function to do the work in the program if you want. Identify the formula, in this case it could be: Farenheit = Celcius X 1.8 + 32. (I think) Your function could look like this... (Toggle Plain Text) float convert( float a ) { float temp_farenheit = ( (temp_celcius * 1.8) + 32 ); return (0); } float convert( float a ) { float temp_farenheit = ( (temp_celcius * 1.8) + 32 ); return (0); } Let the user enter the temp in Celcius, then pass that `float` value as an argument to the function above, then display the 'converted' result on - screen... (`%.2f` will display to two decimal places, `%.3f` to three, etc.) (Toggle Plain Text) printf("Temperature in Celcius = %.2f ", temp_celcius printf("Temperature in Farenheit = %.2f ", convert( temp_celcius ); printf("Temperature in Celcius = %.2f ", temp_celcius printf("Temperature in Farenheit = %.2f ", convert( temp_celcius ); >BstrucT __________________ Be kinder than necessary because everyone you meet is fighting some kind of battle.

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Programming Forums > Application Development > C

Converting Temperatures