Reversing array elements in C programming - c

Question

I am new to C and I have a problem. I need to reverse the elements of arrays in the following program. Can I get a very simple explanation of what I am doing wrong and how I could go on about fixing it?
Here's the output I get:
Enter number 0: 0
Enter number 1: 1
Enter number 2: 2
Enter number 3: 3
Enter number 4: 4
Enter number 5: 5
Enter number 6: 6
Enter number 7: 7
Element 0 is: 7
Element 1 is: 6
Element 2 is: 5
Element 3 is: 4
Element 4 is: 4
Element 5 is: 5
Element 6 is: 6
Element 7 is: 7
My code:
#include <stdio.h>
void reverse(int a[], int i)
{
int j=7,b;
for (i=0; i<=7; i++)
{
b=a[i];
a[i]=a[j];
a[j]=b;
printf("Element %d is: %d\n", i,a[i]);
j--;
}
}
int main(void)
{
int a[8];
int i;
for(i=0;i<=7;i++)
{
printf("Enter number %d: ",i);
scanf("%d", &a[i]);
}
reverse(a, 8);
return 0;
}

Answer 1

To avoid being misled, write the output after the reversal, not during it:
#include <stdio.h>
void reverse(int a[], int i)
{
int j = 7, b;
for (i = 0; i <= 7; i++)
{
b = a[i];
a[i] = a[j];
a[j] = b;
j--;
}
}
int main(void)
{
int a[8];
int i;
for (i = 0; i <= 7; i++)
{
printf("Enter number %d: ",i);
scanf("%d", &a[i]);
}
reverse(a, 8);
for (i = 0; i <= 7; i++)
{
printf("Element %d is: %d\n", i, a[i]);
}
return 0;
}
Now you’ll notice the array isn’t changing at all. That’s because you’re swapping every element in the array twice: once to its reversed position, then back to its original position. To fix this, only loop over the first half the array, i.e. while i < 4.
It was probably also intended to make the second argument to reverse the length, so you should make use of that instead of hard-coding 7 or 4:
void reverse(int a[], int length)
{
int i, j = length - 1, b;
for (i = 0; i < length / 2; i++)
{
b = a[i];
a[i] = a[j];
a[j] = b;
j--;
}
}

Answer 2

You could also copy over the array in a new one:
#include <stdio.h>
void reverse(int a[], int i)
{
int b[i];
int j;
for(j=0; j<i; j++){
b[j] = a[i-1-j];
printf("Element %d is: %d\n", j, b[j]);
}
}
int main(void)
{
int a[8];
int i;
for(i=0;i<=7;i++)
{
printf("Enter number %d: ",i);
scanf("%d", &a[i]);
}
reverse(a, 8);
return 0;
}

Answer 3

What you want to do it move through only half of the length of your array else you're reversing the array twice.
void reverse(int a[], int len)
{
int i;
int j=len-1,b;
for(i=0;i<len/2;i++)
{
b=a[i];
a[i]=a[j];
a[j]=b;
j--;
}
for(i = 0; i < len; i++) {
printf("Element %d is: %d\n", i,a[i]);
}
}

Answer 4

The Principe is simple. just stand at the middle of the table and reverse the elements as follow. so pose n is lent of the table. then the last element is n-1.
so you ave to reverse position t[0] and t[n-2]
reverse t[1] and t[n-3] and so on...
stop when you rich the middle of the table. try to code your self is better than for me giving you the code.
hope it helped.