Floating-point numbers are not printed - c

Question

I am trying to create a conversion table using the C programing language. I want to convert the temperature from -250 °F to 250 °C increments of 10. However, I am not getting the Celsius output:
#include <p18f458.h>
#include <stdio.h>
#pragma config WDT = OFF
#define LOWER -250 /* lower limit of table */
#define UPPER 250 /* upper limit */
#define STEP 10 /* step size */
void main(void)
{
int fh, cel;
cel = (fh - 32) * 5 / 9;
for (fh = LOWER; fh <= UPPER; fh = fh + STEP)
printf("%d \t %6.1f\n", fh, cel);
while(1);
}
Fahrenheit Celsius
-250
-240
-230
-220
-210
-200
-190
-180
-170
-160
-150
-140
-130
-120
-110 .......
The code runs on a PIC18F458 microcontroller.

Answer 1

Recalculate each time
Use floating point math
// dddd123456789012ffffff
puts(" Fahrenheit Celsius");
// cel = (fh - 32) * 5 / 9;
for (fh = LOWER; fh <= UPPER; fh = fh + STEP) {
double cel = (fh - 32.0) * 5.0 / 9.0;
printf(" %4d %6.1f\n", fh, cel);
}
If wanting to avoid floating point types and math, use a scaled integer math to calculate decidegrees to achieve "%6.1f" like output. Scale temperature by 10. Integer division truncates the fraction, so add a signed offset of 5 to form a rounded result.
int offset = (fh - 32) > 0 : 5 : -5;
int deci_celcuis = ((fh - 32) * 10 * 5 + offset) / 9;
Printing is a little tricky. Various approaches exist.
int whole = deci_celcuis/10;
int frac = deci_celcuis%10;
char *sign = (whole < 0 || frac < 0) ? "-", "";
printf(" %4d %s%d.%d\n", fh, sign, abs(whole), abs(frac));

Answer 2

As others have noted: 1) use floating point to avoid integer division and truncation errors, 2) recalculate values inside the loop.
It would be a shame to miss this opportunity to produce parallel tables of F->C and also C->F for the given range.
#define LOWER -250
#define UPPER 250
#define STEP 10
int main() {
puts( " F C C F" );
for( int i = UPPER; i >= LOWER; i -= STEP ) {
printf( "%6.0f %6.0f", (double)i, (i - 32.0) * 5.0 / 9.0 );
printf( " " );
printf( "%6.0f %6.0f\n", (double)i, i * 9.0 / 5.0 + 32.0 );
}
return 0;
}
F C C F
250 121 250 482
240 116 240 464
230 110 230 446
220 104 220 428
210 99 210 410
200 93 200 392
// omitted...
-220 -140 -220 -364
-230 -146 -230 -382
-240 -151 -240 -400
-250 -157 -250 -418
Ordinary mercury thermometers condition people to expect warmer temperatures at the top, and cooler temperatures 'below'... This table reverses the sequence presented in the OP to conform to people's expectations.

Answer 3

cel = (fh - 32) * 5 / 9;
This statement is outside the loop, hence it will only ever print once.
. Add it in the loop and your code would work as expected.