Help with a bubble sort

Gaz

Hi guys,

Hoping someone can look at my code and tell me what im doing wrong, program compiles but dosnt work. Basically ive written a function to bubble sort an array of floats.

void bubble_sort(float *distances, int num_of_els)
{
int num_swaps=0;
int i;
float temp;
do
{


for(i=0; i<num_of_els-1; i++)
{
if(distances<distances[i+1])
{
temp=distances;
distances=distances[i+1];
distances[i+1]=temp;
}
num_swaps++;

}
}
while(num_swaps!=0);


{
for(i=0; i<num_of_els; i++)
printf("%f\n", distances);
}

}


I think its just a syntax issue but I cant spot it

Appreciate any help you guys can offer.
Thanks

km991148

Gaz wrote: »

Hi guys,

Hoping someone can look at my code and tell me what im doing wrong, program compiles but dosnt work. Basically ive written a function to bubble sort an array of floats.

void bubble_sort(float *distances, int num_of_els)
{
int num_swaps=0;
int i;
float temp;
do
{


for(i=0; i<num_of_els-1; i++)
{
if(distances<distances[i+1])
{
temp=distances;
distances=distances[i+1];
distances[i+1]=temp;
}
num_swaps++;

}
}
while(num_swaps!=0);


{
for(i=0; i<num_of_els; i++)
printf("%f\n", distances);
}

}


I think its just a syntax issue but I cant spot it

Appreciate any help you guys can offer.
Thanks

Havent really looked at the algorithm (and been a good while sinceI even thought about a bubble sort) but did you mean to do:

do{
//
//

}
while(num_swaps != 0)

as num_swaps is always gonna be zero?

What ide are you using, are you able to debug/ step through code?


EDIT: sorry missed the num_swaps++
BUT - I see your issue now - you will still be stuck in a loop...!

ressem

You need to reset num_swaps to zero each time the do-while loop restarts.

km991148

Also - why this part?

{
for(i=0; i<num_of_els; i++)
printf("%f\n", distances);
}

The brackets don't add value here - did you intend to place an if before?

Gaz

Thats to print the sorted elements once the bubble sort is finished.
Dosnt feckin work though.

km991148

Gaz wrote: »

Thats to print the sorted elements once the bubble sort is finished.
Dosnt feckin work though.

ok 2 points - did you try and fix the loop as ressem and I suggested?

and 2. - I realise its to print the results, but you have additional braces ({}) around the for which are not needed - why did you add them?

Also - what environment are you using? Visual Studio, eclipse etc? you should be able to step through code/ debug this quite easily.

Why is it 'not working' The code you posted will never reach the print statement as the code will never leave the loop. This can be easily seen in a decent ide. If you are doing this via notepad etc, then you could easily have moved the print statement to before the sort and you would see this.

carveone

Wow. So much wrong

This:
for(i=0; i<num_of_els-1; i++)

should be:
for(i=0; i<num_of_els-2; i++)

for starters. Otherwise you're baling off the end of the array.

Plus, as km said, you need to reset num_swaps (at the start of the do while block). Plus the num_swaps++ needs to be inside the if(distances<distances[i+1]) block.

km991148

carveone wrote: »

Wow. So much wrong

yep - I was going on the basis of one at a time while trying to encourage use of the available tools

Let us know how you go,
km

Gaz

Solved !

I took a different approach and used a nested for loop >>

void bubble_sort(float *distances, int num__of_els)
{
int i;
int j;
float temp;


for(i=0; i<num_of_els; i++)
for(j=num_of_els-1; j>=i; j--)
{
if(distances[j-1]>distances[j])
{
temp=distances[j-1];
distances[j-1]=distances[j];
distances[j]=temp;
}
}

Then a printf printed them in order.

this made much more sense in my head.

thanks guys

amen

Glad you sorted it but

I think its just a syntax issue but I cant spot it

as it compiles it is not really a syntax issues but a logic issue

carveone

Interesting move straight to the optimised case for bubble sort

For stuff like this you are almost always better writing pseudo code on a piece of paper or something and then translating that to code. Otherwise you tend to flail and type things you hope will work but probably won't.

Of course bubble sort isn't exactly a good algorithm. It's pretty appalling in fact!