bubble sort not sorting properly-CodePudding

Im trying to sort this random generated array, but my output isincorrect it looks like this:

sorted round: 0: 87
sorted round: 0: 78
sorted round: 0: 16
sorted round: 0: 94
sorted round: 0: 36
sorted round: 0: 93
sorted round: 0: 50
sorted round: 0: 22
sorted round: 0: 63
sorted round: 0: 28
sorted round: 0: 91
sorted round: 0: 60
sorted round: 0: 64
sorted round: 0: 27
sorted round: 0: 41
sorted round: 0: 73
sorted round: 0: 37
sorted round: 0: 12
sorted round: 0: 69
84
78
16
87
36
93
50
22
63
28
91
60
64
27
41
73
37
12
69 0

ive been at this for hours and havnt been able to figure out what im doing wrong, any help is appreciated.

#include <stdio.h>
#include <iostream>
#include <algorithm> // for std::find
#include <iterator> // for std::begin, std::end
using namespace std;

int main()
{
    int random_array[20];
    int i;
    int j;
    random_array[0]=rand()%(100-1 1) 1;

    for (i=1; i<20;)
    {
        j= rand()%(100-1 1) 1;
        bool exists;
        exists = find(begin(random_array), end(random_array), j) != end(random_array);
        if(!exists)
        {
            random_array[i]=j;
            i=i 1;
        }
        else
        {
            ;
        }
    }
    int size=20;
    i=0;
    j=0;
    int k =0;
    
    for (i; i < size; i  ) {
        for (j; j < size - i; j  ) 
        {
            for(k; k<20; k  )
            {
                cout<<"sorted round: "<<j<<": "<<random_array[k]<<endl;
            }
            if (random_array[j] > random_array[j   1]) {
                swap(random_array[j], random_array[j   1]);
                
            }
            else
            {
                ;
            }
            
           
        }
    }
    for (i=0; i<20;i  )
    {
        cout<<random_array[i]<<endl;
    }
    
    return 0;
}

The out put should be a sorted array called random_array and the issue im running into starts on this line of code:

int size=20;
    i=0;
    j=0;
    int k =0;
    
    for (i; i < size; i  ) {

CodePudding user response：

In these nested for loops

for (i; i < size; i  ) {
    for (j; j < size - i; j  ) 
    {
        for(k; k<20; k  )
        {
            cout<<"sorted round: "<<j<<": "<<random_array[k]<<endl;
        }
        if (random_array[j] > random_array[j   1]) {
            swap(random_array[j], random_array[j   1]);
            
        }
        else
        {
            ;
        }
        
       
    }
}

neither variable j nor the variable k are reset to 0 in each iteration of the most outer loop

for (i; i < size; i  ) {

At least you should write

for (i = 0; i < size; i  ) {
    for (j = 0; j < size - i; j  ) 
    {
        for(k = 0; k<20; k  )
        {
            cout<<"sorted round: "<<j<<": "<<random_array[k]<<endl;
        }
        if (random_array[j] > random_array[j   1]) {
            swap(random_array[j], random_array[j   1]);
            
        }
        else
        {
            ;
        }
        
       
    }
}

Pay attention to that the program invokes undefined behavior in the first iteration of the most outer loop that is when i is equal to 0 because in this if statement

        if (random_array[j] > random_array[j   1]) {

the expression random_array[j 1] accesses memory beyond the array when j is equal size - 1.

It is better to start the inner for loop with 1

    for (j = 1; j < size - i; j  ) 
    {

and in if statement to write

        if (random_array[j-1] > random_array[j]) {