Write a C program to count number of digits in any number

Question

What am i doing wrong in this code ? There are no errors but if i enter a 4 digit number the output it is 1272 !!

#include<conio.h>
#include<stdio.h>
void main()
{
    int i,n=0;
    clrscr();
    printf("Enter a number");
    scanf("%d",&i);
    while(i>=9)
    {
        i=i/10;
        n++;
    }
    n++;
    printf("This is a %d digit number",n);
    getch();
}

You could use a debugger to step through your code and find out by yourself? — Uwe Keim, Apr 15 '17 at 04:55
There is no such header file called `` in standard C. `void main()` is also wrong, it should be `int main(void)` — Destructor, Apr 15 '17 at 04:59
@Destructor `void main()` may not be wrong. It is implementation defined if it is acceptable. Still, best to return `int`. — chux - Reinstate Monica, Apr 15 '17 at 05:09
`while(i>=9) { i=i/10; n++; }` is not correct. Hint: what if `i == 9`? — chux - Reinstate Monica, Apr 15 '17 at 05:22
"count number of digits in **any** number" --> Code has trouble with negative numbers. — chux - Reinstate Monica, Apr 15 '17 at 05:25
@chux Yes,it is having trouble with negitive numbers !! Can you please suggest how to overcome that problem ? — Utkarsh HK, Apr 15 '17 at 05:29
[How to debug small programs](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) — phuclv, Apr 15 '17 at 06:34

msc · Accepted Answer · 2017-04-15T05:28:59.857

It's undefined behavior because you have used uninitialized local variable.

Do not use automatic storage variable before it has been initialized yields undefined behavior

C standard is 6.3.2.1 p2:

If the lvalue designates an object of automatic storage duration that could have been declared with the register storage class (never had its address taken), and that object is uninitialized (not declared with an initializer and no assignment to it has been performed prior to use), the behavior is undefined.

Just initialize your variables and avoid a potential headache in the future.

So, in your program initialize n to 0.

int n = 0;

score 1 · Answer 2 · edited Apr 15 '17 at 05:27

1

Initialize n to 0. You are incrementing whatever garbage value is in memory for n.

edited Apr 15 '17 at 05:27

msc

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answered Apr 15 '17 at 05:05

starlight

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Write a C program to count number of digits in any number

2 Answers2