kind of problem bothering me ( pow or * ? )

ok i have this code

Code:

---

#include <stdio.h>
#include <math.h>

int main(){
   
    float a,b,c;
   
    for (a=1;a<=12;a++){
       
        for (b=1;b<=12;b++){
           
              for (c=1;c<=12;c++){
                 
                  if (a*a+b*b==c*c){
                 
                              if (a+b+c==12){   
                                                   
                              printf("%.0f = %.0f\n",a*a+b*b,c*c);
                              printf("%.0f\n%.0f\n%.0f\n",a,b,c);
                              printf("a+b+c = %.0f\n",a+b+c);
                              printf("-----------------------\n");
                              printf("Final Result: %.0f\n",a*b*c);
                             
                              }
                             
                            }
                        }
                  }
            }
       
        getchar();
       
    return 0;
   
}

---

it shows up the answer i want:

Code:

---

25 = 25
3
4
5
a+b+c = 12
-----------------------
Final Result: 60
25 = 25
4
3
5
a+b+c = 12
-----------------------
Final Result: 60

---

but why doesnt it show anything when using pow instead of *?

Since pow() is not in your code, it's kind of hard to tell what you mean.

If you are using gcc, you must compile "gcc -lm" (link math) to actually use math.h

im using dev C++

btw here is the code using pow

Code:

---

#include <stdio.h>
#include <math.h>

int main(){
   
    float a,b,c;

    for (a=1;a<=12;a++){
       
        for (b=1;b<=12;b++){
           
              for (c=1;c<=12;c++){
                 
                  if (pow(a,2)+pow(b,2)==pow(c,2)){
                 
                              if (a+b+c==12){   
                                                   
                              printf("%.0f = %.0f\n",pow(a,2)+pow(b,2),pow(c,2));
                              printf("%.0f\n%.0f\n%.0f\n",a,b,c);
                              printf("a+b+c = %.0f\n",a+b+c);
                              printf("-----------------------\n");
                              printf("Final Result: %.0f\n",a*b*c);
                             
                              }
                             
                            }
                        }
                  }
            }

        getchar();
       
    return 0;
   
}

---

Are you compiling it as ".C" or ".CPP" coz the code you gave worked fine with my compiler.

as .C

dunno, it s not working for me :S

What is the program output, simply a blank DOS screen or something else?

Apparently dev c++ uses gcc, so you could test this by compiling the program on the command-line:

gcc -o myprog myprog.c -lm

Now run "myprog" and see if it works...

it shows only a blank DOS screen

also i used gcc -o myprog ...

but it didnt work,

'gcc' is not recognized as an internal or external command,
operable program or batch file.

It doesn't show anything because the code is wrong. Well, actually, it's not really wrong, it just won't do exactly what you expect.
The reason is that both a*a and pow(a, 2) are not exact numbers when represented as a floating point number. The latter always is; the first only when a is a floating point number. So there may be (and in your second case, there is) a difference in what you expect the value to be and what the value really is.

So to solve this, don't compare floating point numbers directly. Take the difference between two you want to compare and make sure it's close enough to the value you want. For instance, if you want to compare a and b, do something like:

Code:

---

if(abs(a - b) < 1e-12) {
  // Numbers are equal
}

---

I'll leave it up to you to do this in your program.

Quote:

---

The reason is that both a*a and pow(a, 2) are not exact numbers when represented as a floating point number.

---

I also think that's the problem but I don't understand how the multiplication version and the pow version differ given that both use float variables. Do you suppose the compiler is somehow knowing to do integer arithmetic?

As long as you're storing integers in 'float' types, then yes, simple multiplication by itself results in more integers. Whereas if you use pow() you're going to get some round-off issues where the results differ from integers by a few bits. pow() uses logarithms internally, not simple sequences of multiplies. After all, it can not predict if you're going to pass it some huge and/or non-integer exponential.

I suppose if the library function writers felt it was worth it they could build in short-cuts for low exponentials so that simple multiplication is used when possible. But I figure checks for that and the overhead in time penalties aren't worth the effort.