scanf（）到C中的一维数组

Question

I'm having problems reading user inputs from terminal into my array.

the array 'a' has a dynamic size. The polynomial which is inputted by the user determines the size of the array.

once compiled and run:

Enter the order number:
3
Enter your constant:
-90
Enter coefficient # 0
8
Enter coefficient # 1
4
Enter coefficient # 2
35
Enter coefficient # 3
54
  0     8.000000
  1     4.000000
  2     0.000000
  3     0.000000

On the debug lines I'm just reporting the array back to user. For some reasons it returns zero for the second half of the array. I can't figure out what the problem could be. Any help would be greatly appreciated.

PS. ignore eval function.

here is the code I'm working on:

//import required libraries
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

// function prptotype
double eval(double a[], double x, int n); //n is max degree
//global variables
int N = 0;//N is the polynomial order
double *a;//array
double  x; // constant
//main function
int main()
{
    printf("%s\n", "Enter the order number:");
    scanf("%d", &N); // user input for the order numbers
    while (N < 1) //input debuger
    {
        printf("%d %s\n%s\n", N,"is NOT a positive and non-zero number", "Enter a positive and non-zero integer:" );
        scanf("%d", &N); // user input for the order numbers
    }
    a = malloc ((N + 1) * sizeof(int));// assigning the array size in respect with user input
    printf("%s\n", "Enter your constant:" );
    scanf("%lf", &x);// user input for "x" constant
    for (int i = 0; i < N + 1; ++i)
    {
        printf("Enter coefficient # %d\n", i);
        scanf ("%lf", &a[i]);
    }
    /* Debug */
    for (int i = 0; i < N + 1; ++i)
    {
        //a[i] = 0;
        printf("%3d%13lf\n", i, a[i]);
    }
}

//eval function
double eval(double a[], double x, int n)
{

}

Answer 1

First problem is this -

a = malloc ((N + 1) * sizeof(int));  //you allocate for N+1 integers

You don't allocate enough memory(you need to allocate for N+1 double ) . a is a double * and you use sizeof(int) . Correct it to -

a = malloc ((N + 1) * sizeof(double));

And thing for printing double use %f not %lf (only for scanf )-

printf("%3d%13lf\n", i, a[i]); // -> use %f
              ^^

Note - Don't forget to free allocated memory. And BTW no array in your code .