unable to sort an array, wrong output - c++

Question

#include<bits/stdc++.h>
using namespace std;
int
main ()
{
int a[3] = { 3, 2, 1 }, i, j, t = 0, k = 0;
int m;
for (int i = 0; i < 2; i++)
{
m = a[i];
for (int j = i++; j < 3; j++)
{
if (m > a[j])
{
m = a[j];
k = j;
}
}
t = a[i];
a[i] = m;
a[k] = t;
}
for (int i = 0; i < 3; i++)
{
cout << a[i];
}
return 0;
}

Answer 1

You seem to want to implement an insertion sort algorithm by hand. For this task, you should consider using std::sort. I refactored your code such that it basically does the same thing as you wanted and included some tips to make the code more readable and easier to debug for you and others:
#include <algorithm> //only include necessary headers
#include <iostream>
//do not use "using namespace std"
int main ()
{
int a[3] = { 3, 2, 1 };
/*
Declare local variables at the first point they are used an as local as possible.
It is much easier to read, if a no longer necessary variables leaves scope.
*/
for (int i = 0; i < 2; i++) {
int min = a[i]; //use names that tell something about what you are doing
int bestIndex = i;
for (int j = i+1; j<3; j++) { //here was your major bug: i++ also increcments i
if (a[j] < min){
min = a[j];
bestIndex = j;
}
}
std::swap(a[i], a[bestIndex]);
//try to use standard algorithms as often as possible. They document your code, are optimized and easier to read.
}
for (int i = 0; i < 3; i++){
std::cout << a[i];
}
return 0;
}

Answer 2

Look at this:
for (int i = 0; i < 2; i++)
{
for (int j = i++; j < 3; j++)
{
}
}
On the first iteration of the outer loop:
i is 0.
Then the inner loop increments it to 1.
Then the outer loop increments it to 2.
Then the outer loop is done, after just one iteration.
You want i+1 in the inner loop, not i++.

Answer 3

#include<bits/stdc++.h>
using namespace std;
int main ()
{
int a[3] = { 3,2,1}, t = 0, k = 0;
int m=0;
bool flag_change =false;
for (int i = 0; i < 2; i++)
{
m = a[i];
for (int j = i+1; j < 3; j++)
{
if (m < a[j]) //changing sing (<>) sort by ascending/sort by descending order
{
m = a[j];
k = j;
flag_change = true;
}
}
if(flag_change)
{
t = a[i];
a[i] = m;
a[k] = t;
flag_change = false;
}
}
for (int i = 0; i < 3; i++)
{
cout << a[i];
}
return 0;
}
I'm done correct you code. Code is working.But it is not good implementation.