C programming Do – While loop problems

[JJ452]

Hi,
I have to build a program that will find the equivalent resistances in series and parallel of any number of resistances entered at the keyboard. So far i have this:

/*

TITLE- q4__4.c 2/10/06
DESCRIPTION- Calculates the effective resistance of a entered number of resistors in series and in parallel
*/

/* Include standard input ouput library */

#include <stdio.h>


main()

{
/* local variables go here */
double RTS,RTP,LOOPS,X,loop_count;

/* The Number of Resistors */

printf("How many resistors would you like to calculate a value for?");
scanf("%lf",&LOOPS);

/* The loop statement */

loop_count=0;
RTS=0;
RTP=0;

do
{
printf ("Enter a value for resistance >");
scanf("%lf",&X);
RTS += X;
RTP += (1/X);

loop_count = (loop_count + 1);
}while (loop_count < LOOPS);

/* The Result */
printf ("\nThe Total resistance is %lf if they are in series and %lf they are in parallel."),RTS,(1/RTP);

I really don't know where i went wrong. The value returned for RTS is the same value as the user entered and the value returned for RTP is the last value for the resistor entered. I reckon it's a problem with the loop but what it is i don't know. Help please?

 

[mgb_phys]

How many times does the loop execute?
To test it print the value of x,rts, rtp and loop count inside the loop.

ps. It's a bad idea to use floating point for loop counters, use integers.

 

[JJ452]

How many times does the loop execute?
To test it print the value of x,rts, rtp and loop count inside the loop.

ps. It's a bad idea to use floating point for loop counters, use integers.

It executes as many times as the user entered (The number of resistors they have) because the program compiles and asks for that number of resistances but, for some reason, doesn't seem to add the 'X' value (the resistance entered) correctly. I can't use integers as it will have decimals which could be small and a value of 1 or 0 wouldn't be accurate enough.

 

[mgb_phys]

Had to actualy test this - it's a very subtle error.
The line printf ("blah"),RTS,(1/RTP);

Is wrong - note the misplaced closing bracket for printf
what the compiler see is printf("blah blah"); RTS; 1/RTP; As three separate statements.

Printf is missing the arguments for the %f calls, so it just uses whatever is on the stack next - which happens to be the last values entered in scanf ( because they use the same temporary storage). the extra RTS and 1/RTP statements are just ignored.

It should be printf ("blah",RTS,(1/RTP));

If you compiled with warnings on ( eg /Wall in gcc) it shoudl tell you - MS c compiler didn't tell me!

ps. I mean use integers for counters in the loop, the number of times around the loop MUST be an integer - you can't enter 0.1 resistor values.

 

[JJ452]

Thanks for your advice and help, it was great.