Using Array Integer

Question

I'm new in C programming language.
I need to get every digit separately that user have entered.
Here is my code:

#include <stdio.h>

int main()
{
    int n[100];
    printf("Enter a number: ");
    scanf("%d",&n);
    printf("%d %d %d",n[1],n[2],n[3]);

   return 0;
} //i know that my code is not assigning like i want.

and now for example user entered a number like 123, i want the output like 1 2 3,
How can i assign every digit to n[i] ?
Without using string to int or int to string like atoi?
Here is what Im going to do:
User will enter a number and the program will search from Matrix 100x100 in row or column. i think i need to get the every digit separately to search.

i need to get the number(user have entered) as integer bcuz user might enter minus or the number starts with 0. at that time the program will do another operation! — user3722549
– user3722549, Commented Jun 9, 2014 at 14:01
It's unclear exactly what you need. Please specify some sample input and the corresponding output. If you claim that getchar doesn't work, provide sample input for that as well. — pts
– pts, Commented Jun 9, 2014 at 14:03
The answer that is posted below is right, it's up to you to figure out how to store the negative-flag of the number. — Happington
– Happington, Commented Jun 9, 2014 at 14:04

Ivaylo Strandjev · Accepted Answer · 2014-06-09 14:01:55Z

3

No need to go to character array. The lats digit of a number n can be computed using n%10. Then you can remove the last digit using n /= 10. So this cycle would print the digits in reverse order:

void print_rev_digits(int n) {
  while (n) {
    printf("%d\n", n%10); 
    n /= 10;
  }
}

And using a stack you can print the digits in the correct order. You can also use recursion for this(which will use stack for you). I am deliberately not posting a complete solution.

answered Jun 9, 2014 at 14:01

Ivaylo Strandjev

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4 Comments

user3722549 Over a year ago

its not just for printing out. I`ll use it to search in big code. and also i would be glad if u explain whats that %10 and in while loop why there is only one 'n' ? as i said im new in programming

Ivaylo Strandjev Over a year ago

@user3722549 % is binary operator and it returns the remainder of its first operand after integer division by its second operand. There is only one n in the function - the function argument.

user3722549 Over a year ago

n[100] user might enter a larg number at that time this code can work fast enough ?

Ivaylo Strandjev Over a year ago

@user3722549 you are reading a single integer and the maximum value an integer can possibly have is about 2^32(for most modern computers). Thus you will not be able to enter a 100 digit number this way. You will have to read in a 100 character string to be able to read such input.

Sergey L. · Accepted Answer · 2014-06-09 14:14:51Z

0

In this case you should read the user input character by character:

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>

int main()
{
    char input[100];
    int n[100];
    printf("Enter a number: ");
    if (fgets(input, sizeof(input), stdin)) { // attempt to read a line
        int i;
        for (i = 0; input[i]; i++) { // for each entered character
            if (input[i] >= '0' && input[i] <= '9') { // is a digit
                n[i] = input[i] - '0';
                printf("%d ", input[i] - '0');
            } 
            else if (isspace(input[i])) // end of entered integer
                break;
            else {
                printf(stderr, "Input is not a number\n");
                return -1;
            }
        }
        printf("\n");
    } else {
        fprintf(stderr, "User did not enter valid input.\n");
    }

   return 0;
}

answered Jun 9, 2014 at 14:14

Sergey L.

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2 Comments

user3722549 Over a year ago

i think its no difference than getchar and what if user entered -123 ? hey but i want to know that return -1 , is it difference than return 0 ?

Sergey L. Over a year ago

The return value from main will be passed as an exit code to the parent who called. As a convention 0 indicates that the program exited normally and any other value that it exited abnormally. Sometimes a non-zero exit code will allow the parent to determine the cause of the abnormal exit. In this case it just indicates that the program exited abnormally with an error coded -1, whatever that means is up to you to interpret :)

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