Logical error in a C program to calculate the numbers of digits in an integer-CodePudding

I made this program to calculate of digits of an integer in C. This program works well until I give an input of 10 digit number. If I give input of an integer with a digit of more than 10 digits, the behavior of the code changes.

// Program to calculate the number of digits in an integers.

#include <stdio.h>

int main()
{
    int number;
    int count = 0;

    printf("Enter a number: ");
    scanf("%d", &number);
    while (number != 0)
    {
        number = number / 10;
        count  ;
    }
    printf("The number of digits in an integer is : %d", count);
}

For example:

Output of program: 
$ gcc digits.c && ./a.out
Enter a number: 1234567890
The number of digits in an integer is : 10

The expected output is executed successfully. Let's see one more example.

Output of program:
$ gcc digits.c && ./a.out
Enter a number: 12345678901234567890
The number of digits in an integer is : 1

Here, I gave input of 20 digits of an integer but it's returning 1 digit. I don't understand why this happens?

Can someone please explain to me what's the logical mistake I did in my code?

CodePudding user response：

integers can only store values from -2147483648 to 2147483647. if you change to unsigned long long it will work.

#include <stdio.h>

int main()
{
    unsigned long long number;
    int count = 0;

    printf("Enter a number: ");
    scanf("%llu", &number);  // use %llu here
    while (number != 0)
    {
        number = number / 10;
        count  ;
    }
    printf("The number of digits in an integer is : %d", count);
}

output:

Enter a number: 12345678901234567890
The number of digits in an integer is : 20

CodePudding user response：

The number you are inputting is too big to be stored in an int. An int can (usually) store numbers from -2,147,483,648 to 2,147,483,647. Try declaring number as an unsigned long that (usually) stores numbers from 0 to 18,446,744,073,709,551,615. You could also try storing the digits in an array of some sort and counting the number of elements in it. You could also read the digits one by one (with getchar() for example) and count them on the fly. That eliminates the limitations of number types.