Sorting problems

[rocketjumper]

HI I just started learning c++. Below is the bubble_sorting program I wrote. Complied no error under eclipse(Ubuntu). But the result is not right.

What is happening is, no matter what input numbers I provided, after sorting, the smallest number would be set to zero. Please, can anyone point out where did I do wrong. Many thanks in advance!

//start of the program
//Bubble_sorting

#include <iostream>
using namespace std;

void BubbleSort(int *list,int len)
{
int i,j,temp;
for(i=0;i<len;i++)
for(j=0;j<len-i;j++)
{
if(list[j]>list[j+1])
{
temp=list[j];
list[j]=list[j+1];
list[j+1]=temp;
}
}
}

int main ()
{
int len;
cout<<"input the number of int to sort"<<endl;
cin>>len;
int *p = new int[len];

cout<<"Input ten number:";
for(int i=0;i<len;i++)
cin>>p[i];
cout<<endl;

cout<<"Before sorting: ";
for(int i=0;i<len;i++)
cout<<p[i]<<" ";
cout<<endl;

BubbleSort(p,len);
cout<<"After sorting: ";
for(int i=0;i<len;i++)
cout<<p[i]<<" ";

cout<<endl;
cout<<p[0]<<endl;
cout<<endl;

delete[] p;
p = NULL;
return 0;
}

[ZuK]

You have bufferoverflows in your bubblesort.
And please use CODE tags when posting code.
Kurt

[rocketjumper]

Thanks Kurt! Can you be more specific?

[Paul McKenzie]

Thanks Kurt! Can you be more specific?

for(j=0;j < len-i;j++ )

Assume len is 10 and i happens to be 0. That loop translates to this:

for(j=0;j < 10; j++)

So you will loop from 0 to 9. But your code has this:

if( list[j] > list[j+1])

Which translates to this on the last iteration of the loop

if (list [9] > list[10])

Do you see a problem? You're accessing an invalid array element (list[10]).

Regards,

Paul McKenzie

[rocketjumper]

Thanks Paul! That makes sense now! Just modify the inner for loop as

for(j=0;j<len-i;j++)

will solve the problem! Thanks for explaining this to me

[rocketjumper]

I mean:

for(j=0;j<len-i-1;j++)