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Hi, i am absolute newbie in programming. I am starting with learning C by book "C Programming Language (2nd Edition)" and stuck in very first example where we get exercise to write simple program that prints values of temperatures from lower to upper in 2 columns (tabs) that contains Celsius a Fahrenheit.

I'v get problem because trying to edit those code for:

1. Celsius is main system.


2. Steps measured dynamically by dividing lower on any given number.

And all work perfectly while i am using integers variables.

#include <stdio.h>

main()

 int celcius, farenheit;
 int lower, upper, step;

 lower = -273.15;
 upper = 0;
 step = lower / -10; // Dividing lower temperature by given number

 celcius = lower;

 while (celcius <= upper) 
 farenheit = celcius * 9/5 + 32;
 printf("%dt%dn", celcius, farenheit);
 celcius = celcius + step;
 

But goes to absolutely random numbers when i try using float or double variables for more precise result: (There is code and output in terminal)

#include <stdio.h>

main()

 float celcius, farenheit;
 float lower, upper, step;

 lower = -273.15;
 upper = 0;
 step = lower / -10; // Dividing lower temperature by given number

 celcius = lower;

 while (celcius <= upper) 
 farenheit = celcius * 9/5 + 32;
 printf("%dt%dn", celcius, farenheit);
 celcius = celcius + step;
 

Output:

1610612736 1073741824
1073741824 1073741824
-1073741824 1073741824
1073741824 536870912
-1073741824 536870912
1073741824 0
-2147483648 0
-2147483648 -2147483648
536870912 -1610612736
-2147483648 0

So what happened behind that number magic and how to get this to work?

Two problems: first of all, you are doing integer division which causes your quotient to be truncated. Multiply in your calculations by 9./5., not 9/5. The former gives the actual result, but the latter performs integer division

Your second problem is using %d as your format specifier. You need %f which is for float. Read the man pages for printf for more details on this.

hope this can help you

#include <stdio.h>

int main(int argc,char **argv)

 double celcius, farenheit;
 double lower, upper, step;

 lower = -273.15;
 upper = 0;
 step = lower / -10; // Dividing lower temperature by given number

 celcius = lower;

 while (celcius <= upper) 
 farenheit = celcius * 9/5 + 32;
 printf("%5.2ft%5.2fn", celcius, farenheit);
 celcius = celcius + step;
 
 return 0;