Unable to print numbers entered into an array in reverse order - c

Question

I'm attempting to write a program with an array in which:
The user enters 10 integers, and the integers are then displayed in reverse order, or
The user enters up to 10 integers and exits the while-loop using a 0, and the integers entered are then displayed in reverse order.
The code below is my best effort (my 5th attempt at solving the problem), but it's collecting the integer zero and displaying it in the array index (I've attempted to attach the other five, but it keeps producing an error):
int main()
{
#define ARRAY_LENGTH 10
int numbers[ARRAY_LENGTH];
int numbersEntered = 0;
for (int i = 0; i < ARRAY_LENGTH; i++)
{
numbers[i] = 0;
}
int number = 0;
printf("Enter an integer; 0 to quit: ", ARRAY_LENGTH - 1);
scanf_s("%d", &number);
while (number != 0 && numbersEntered < ARRAY_LENGTH - 1)
{
numbersEntered++;
numbers[numbersEntered] = number;
printf("Enter another integer; 0 to quit: ", ARRAY_LENGTH - 1);
scanf_s("%d", &number);
}
for (int i = numbersEntered; i >= 0; i--)
{
printf("index %d -> %d\n", i, numbers[i]);
}
}

Answer 1

See the problem is first you're initializing the entire array with zero here
for (int i = 0; i < ARRAY_LENGTH; i++)
{
numbers[i] = 0;
}
Then you're doing this
while (number != 0 && numbersEntered < ARRAY_LENGTH - 1)
{
numbersEntered++;
numbers[numbersEntered] = number;
printf("Enter another integer; 0 to quit: ", ARRAY_LENGTH - 1);
scanf_s("%d", &number);
}
So what is happening is, since numbersEntered was already initialized with zero you're incrementing it by 1, so the first digit is entered in the array numbers is 0 as you initialized the entire array itself in the start.
So a quick fix would be just to move it a line down and change the while loop code to this
while (number != 0 && numbersEntered < ARRAY_LENGTH - 1)
{
numbers[numbersEntered] = number;
numbersEntered++;
printf("Enter another integer; 0 to quit: ", ARRAY_LENGTH - 1);
scanf_s("%d", &number);
}
Also as pointed out by Kiran in the comments, the printing for loop needs to be changed to this
for (int i = numbersEntered-1; i > 0; i--)
{
printf("index %d -> %d\n", i, numbers[i]);
}

Answer 2

The line
printf("Enter an integer; 0 to quit: ", ARRAY_LENGTH - 1); should be
printf("Enter an integer; 0 to quit: ");
You should use scanf not scanf_s
The following code could work:
#include <stdio.h>
#define ARRAY_LENGTH 10
int main()
{
int numbers[ARRAY_LENGTH];
int i;
int k;
for (k = 0; k != ARRAY_LENGTH; ++k)
{
printf("Enter an integer; 0 to quit: ");
if (scanf("%d", numbers + k) != 1 || numbers[k] == 0)
break;
}
for (i = k - 1; i >= 0; --i)
printf("index %d -> %d\n", i, numbers[i]);
return 0;
}

Answer 3

This here is a solution of mine which includes some good practices, that is a tweak of your code:
1) you would want your defines outside of a function (or main) so that you can use the same constant in the entire program;
2) any function that has a return type (e.g int main) must return something at the end, thus you must have a "return 0" at the end of your main function;
3) the do-while part will ensure that your piece of code will be executed once before the while condition is checked;
4) numbers[numbersEntered++] = number; will assign to "numbers[numbersEntered]" the value of "number" and then will increment "numbersEntered" by one; This is to reduce the amount of code that you have to write :);
Hope this helped, and if you have more questions, I hope I can answer them :).
#define ARRAY_LENGTH 10
int main()
{
int numbers[ARRAY_LENGTH];
int numbersEntered = 0;
for (int i = 0; i < ARRAY_LENGTH; i++)
numbers[i] = 0;
int number = 0;
do
{
printf("Enter an integer; 0 to quit: ");
scanf_s("%d", &number);
if (number == 0)
break;
numbers[numbersEntered++] = number;
} while (number != 0 && numbersEntered < ARRAY_LENGTH);
if (numbersEntered > 0)
{
for (int i = numbersEntered - 1; i >= 0; i--)
printf("index %d -> %d\n", i, numbers[i]);
}
return 0;
}

Answer 4

I think it's because you are not inserting any number to the first place in the array (place[0]), because you are prompting the value of numbersEntered too early. Try to write your loop this way:
while (number != 0 && numbersEntered < ARRAY_LENGTH - 1){
numbers[numbersEntered] = number;
printf("Enter another integer; 0 to quit: ", ARRAY_LENGTH - 1);
scanf_s("%d", &number);
numbersEntered++;
}