Question

I need to limit the input from a user to only positive values, and count the number of digits in that number. The user will only type in a (+/-) whole number up to 9 characters long.

I’m only allowed to use the scanf function and for, while, or do-while loops.(I saw in similar questions how to do this using getchar, but I can only use scanf). I’m not allowed to use arrays, or any other library besides stdio.h and math.h

I know that if I write:

n=scanf(“%c%c%c%c%c”,&a,&b,&c,&e,&f);

n will count the number of successful scanf conversions.

The problem i’m having is that when I define the input with char, it does everything I want except that the user MUST enter 5 characters. So if the user wants to input “55” he has to press “5” “5” “enter” “enter” “enter”.

I need the program to move on after the first “enter” but also be flexible to receive a number up to 9 digits long.

again, I can’t use getchar or anything fancy. Just the really basic stuff in C that you learn in the first 2 weeks.

Answer 1

Use scanf to read the number into a long int , then use a for loop with a /10 to count the number of digits

What do you want the program to do in case of a -ve number being entered?

#include<stdio.h>
int main()
{

    long int a;
    int b;
    do
    {
    scanf ("%ld",&a);
    if(a<0)
        printf ("invalid input");
    }while(a<0);

    for(b=0;a!=0;b++,a=a/10);
    printf("%d",b);
}

(does not handle -ve numbers specially)