Output is showing different

Question

#include<stdio.h>
int main()
{   
int a[6]={2,5,4,6,1,3};
int j,key,i,k;   
for(j=1;j<6;++j)
{
    key=a[j];
    i=j-1;
    while((i>=0)&&(a[i]>key))
    {
        a[i+i]=a[i];
        i=i-1;
    }
    a[i+1]=key;
}

for(i=0;i<6;i++)
printf("%d\n",a[i]);
}

When I calculate myself I get 1,2,3,4,5,6 but the output is 2,4,5,6,1,3.

I tried so hard, but couldn't find what is wrong in this.

Answer 1

There is a typo in your program.

Instead of

a[i+i]=a[i];

there shall be

a[i+1]=a[i];

Take into account that according to the C Standard the function main without parameters shall be declared like

int main( void )

Also it is a bad idea to use "raw numbers" throughout the program.

It is desirable to place the sorting into a separate function.

The corresponding program can look like

#include <stdio.h>

void insertion_sort(int *a, size_t n)
{
    for (size_t i = 1; i < n; i++)
    {
        size_t j = i;
        int value = a[i];

        for (; j != 0 && value < a[j - 1]; --j)
        {
            a[j] = a[j - 1];
        }

        if (j != i) a[j] = value;
    }
}

int main( void )
{
    int a[] = { 2, 5, 4, 6, 1, 3 };
    const size_t N = sizeof(a) / sizeof(*a);

    for (size_t i = 0; i < N; i++)
    {
        printf("%2d ", a[i]);
    }
    putchar('\n');

    insertion_sort(a, N);

    for (size_t i = 0; i < N; i++)
    {
        printf("%2d ", a[i]);
    }
    putchar('\n');

    return 0;
}

Its output is

2  5  4  6  1  3
1  2  3  4  5  6

For big arrays it is better to use the binary search instead of sequential comparisons.