Thread: 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 *?

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;
     
}

as .C

dunno, it s not working for me :S

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.

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?