C: How can I split the user input of a number and store it into an array of elements?

Question

I have a number, 321197186 which the user inputs. How can I store this number into an array one element at a time. Basically, I am trying to store the 1st digit into 0th element and so on. And then I have to do some computation on that number.

Answer 1

Represent your number as a string, where every character of that string will be the corresponding digit of your number.

There are a plethora of method to read a string, but I suggest you use fgets() like this:

#include <stdio.h>
#include <string.h>

#define MAX_LEN 10

int main (int argc, char *argv[])
{
    char number[MAX_LEN];
    printf("Enter a number: \n");
    fgets(number, MAX_LEN , stdin);
    printf("%s\n", number);
    return 0;
}

With a for loop, you access the characters (digits) of the string (number) one by one, if you like.

I suggest you also eat the trailing newline that fgets() leaves in the input array, as already explained in Removing trailing newline character from fgets() input.

---

Alternative solution proposed by bruno@:

scanf("%9s", number);

Read more in C - scanf() vs gets() vs fgets().

Answer 2

Assume you have

int num;
if (scanf("%d", &num) != 1)
{
    // Input error
    exit(1);
}

// Now the user input is available in num

then you do

#define MAX_DIGITS 32
int digits[MAX_DIGITS] = { 0 };
int index = 0;
while(num != 0 && index < MAX_DIGITS)
{
    digits[index] = num % 10;
    ++index;
    num = num / 10;
}

// Now the array digits holds the individual digits
// and index holds the number of valid digits

Answer 3

You can consider this logic in C -

number = 321197186
while(number> 0)  -  leave if number becomes 0 
{
    int last_digit = number % 10;  - Last digit from the number
    printf("%d",last_digit);  

    number = number / 10;    - to get the remaining number.
}

This can be also done in Python as -

number = 321197186
list1 = []
for i in str(number):
    list1.append(i)
print(list1)

Answer 4

store this number into an array one element at a time.

Let us take advantage of the input process to have a convenient way to determine the length of input including leading zeros (but not input with a sign, leading spaces) by using "%n" to record the offset of the scan.

Use % 10 to exact the least significant decimal digit of the number.

int number;
int offset;
if (scanf("%d%n", &number, &offset) == 1) {
  int a[offset];  // VLA
  while (offset > 0) {
    a[--offset] = number % 10;
    number /= 10;
  }
  for (int i = 0; i < sizeof a/sizeof a[0]; i++) {
    printf("a[%d] = %d\n", i, a[i]);
  }
}

Output

a[0] = 3
a[1] = 2
a[2] = 1
a[3] = 1
a[4] = 9
a[5] = 7
a[6] = 1
a[7] = 8
a[8] = 6

Answer 5

But as bruno points out, you just have to check it as a string as an user input with fgets is an array of characters (even if we are talking about numbers). For more detail:

for(i=0;i<sizeof(array_input);i++){
     //Store the char into another array
}