Optimizing C Code: Help with Loops and If Statements for Gear Combinations

[herpamad]

Hey

I am having some issues with my C code.

What it should do is calculate the output speed when a gear combination is used. It loops to find all combinations for 4 gears from 1 to 42, but can be changed.

2 things i can't get working

- IF STATEMENT - i want it to only show combintations that fall within a 10% range of the target output speed

- LOOP - Keeps printing 0;s as the answer?

Any help is appreciated.

here is the code

#include <stdio.h>
#include <iostream>
#include <time.h>



 

int main()
{
    
    //
    clock_t start, end;
    int q = 0;

    start = clock();

    for(q = 0; q < 99999999; q++);
    //
    
    
    // Count calculations
    int count = 0;
    
    // Gears
    int n1, n2, n3, n4;

    //Minimum teeth
    int tmin = 1;
    
    //Maximum teeth
    int tmax = 42;
    
    // Input speed
    int N1 = 9700;
    
    //Target Output speed
    int N4_Target = 1950;
    
    //Actual Output speed
    int N4;
    
    //To calculate
    
    int r1, r2;
    
    // Gear n1
    for (n1=tmin;n1<=tmax;n1++)
    {
        //gear n2
        for(n2=tmin;n2<=tmax;n2++)
        {
             //gear n3
             for(n3=tmin;n3<=tmax;n3++)
             {
                  //gear n4            
                  for(n4=tmin;n4<=tmax;n4++)
                  {
                       // RATIO 1
                       
                       r1 = n2/n1;
                       
                       // RATIO 2
                       
                       r2 = n4/n3;
                       
                       // OUTPUT SPEED
                       
                       N4 = (n1*n3)/(n2*n4)*N1;
                       
                       // Lowest possible output speed
                       
                       int low_error = 0;
                       
                       low_error = (N4_Target/100)*90;
                       
                       // Highest possible output speed
                       
                       int high_error = 0;
                       
                       high_error = (N4_Target/100)*110;
                       
                       //printf("Low = %i, High = %i\n",low_error, high_error);
                       
                      if ( N4 <= high_error)
                      {
                  
                              printf("(%i * %i) / (%i * %i ) * %i = %i\n",n1,n2,n3,n4,N1,N4);
                      }
                      else
                      {
                           
                       
                      }

                       
                         count++;
                                   
                                   
                  }
                              
             }
                         
                         
             
        }
        
    }
    
    printf("%i\n\n\n",count);
    
    
    //
     end = clock(); 
     printf("Oeff.. %.2f sec's\n", (double)(end - start) / (double)CLOCKS_PER_SEC); 
     //

    
   system("pause");
   
   
   return 0;  
    
}

 

[CompuChip]

I have my doubts about a gear with 0 teeth :P
But anyway...

- IF STATEMENT - i want it to only show combintations that fall within a 10% range of the target output speed

You are only checking for the upper bound, you are not looking whether N4 >= lower_bound, are you?

- LOOP - Keeps printing 0;s as the answer?

Can you be more specific as to which loop you are referring to? e.g. put a comment line where the 0's are being printed.

    for(q = 0; q < 99999999; q++);

Can you explain the use of that line?
Also, I have my doubt about declaring

int high_error = 0;

inside the loops, I would suggest declaring it outside the loop:

int high_error;
for(...) {
   ...
   high_error = (N4_Target / 100) * 110;
   ...
}

or even not declare it at all:

for(...) {
  ...
  if (N4 <=  (N4_Target * 1.10)) { 
    ...
 }
 ...
}

Finally, what is the use of keeping the "count" variable... isn't it immediately clear that you have (tmax - tmin)⁴ combinations?

 

[herpamad]

Right, thanks for that, all taken and will try streamline the code and repost if i get the same error, thanks.

 

[herpamad]

Here is my second attempt.

First let me shed some light on what i am trying to achieve.


I want to calculate this forumula


((n1 * n3) / (n2*n4)) * N1

Example would be

((12 * 40) /( 30 * 20)) * 9700 = 7760


Doing this, i think i need to change int to a float as some of the divisions are 0.? numbers, and thus an int would just give 0 right?

I want to create an IF that says, if N4 is less than 10% higher than the target, and is more than 10 lower than the target?

like

if (N4 <= N4_Target * 1.10) and (N4 >= N4_Target * 0.9)

the error can be 10% either way of the target, hope this protrays this?

#include <stdio.h>
 
int main()
{

    int n1, n2, n3, n4; // Gears
    int tmin = 12; //Minimum teeth   
    int tmax = 42; //Maximum teeth
    int N1 = 9700; // Input speed
    int N4_Target = 1950; //Target Output speed
    int N4; //Actual Output speed
 
    // Gear n1
    for (n1=tmin;n1<=tmax;n1++)
    {
        //gear n2
        for(n2=tmin;n2<=tmax;n2++)
        {
             //gear n3
             for(n3=tmin;n3<=tmax;n3++)
             {
                  //gear n4            
                  for(n4=tmin;n4<=tmax;n4++)
                  {
                       
                       // OUTPUT SPEED
                       
                       N4 = (n1*n3)/(n2*n4)*N1;
 
                      if ( N4 <= N4_Target * 1.10)
                      {
                  
                              printf("(%i * %i) / (%i * %i ) * %i = %i \n",n1,n2,n3,n4,N1,N4);
                      }
                           
                  }
                              
             }
  
        }
  
    }
    
   system("pause");
       
}

 

[herpamad]

I have made the code so it runs with hard coded values.

Now i want to make a loop so i can get all combinations for n1,n2,n3,n4 from 12 to 42.

ie

12*12 / 12*12 * N1

to

42*42 / 42*42 * N1

Think notation is

12..42*12..42 / 12..42*13..42 * N1

thus calculating all possible numbers, next step would be to use an if to make sure than N4 is only output if its within 10% either way of the target speed.

Am i making sense? if no i will try to elaberate more.

Thanks again for all help

#include <stdio.h>

int main()
{
    float n1=12,n2=40,n3=20,n4=30;
    float N1 = 9700;
    float N4;

    N4 = ((n1*n3)/(n2*n4))*N1;
    
    printf("(%2.0f x %2.0f) / (%2.0f x %2.0f) x %2.0f = %2.0f rpm\n\n",n1,n2,n3,n4,N1,N4);
    
    system("pause");
    
}

and this is the code i have made to calculate every combination

#include <stdio.h>

int main()
{
    
    int i, j, k, l;
    int min = 12, max = 42;
    
    for(i=min;i<=max;i++)
    {
        for(j=min;j<=max;j++)
        {                   
            for(k=min;k<=max;k++)
            {
                for(l=min;l<=max;l++)
                {
                    printf("%i * %i * %i *%i\n",i,j,k,l); 
                } 
            }                       
        }                                   
    }
    
    printf("%i\n",i);  
    system("pause");
 
}

Now i just need to mash them together, but it all goes wrong