Q:

Arrow pointing out wrong input from user in C

The following code lets the user write a number in a string so it will be converted to an integer automatically. However, if he writes something else than a number there should be an error. So far so good it worked.
The problem is now: I need to point an arrow to the letter which is not allowed by the user. 
Example: He writes 45. This is right. He writes 423a4. This is wrong. Then there should be an arrow point on the letter a. 
But I don't know how and where I should put the arrow.
NOTE: NO LIBRARY FUNCTIONS ALLOWED except stdio.h
Here is the code:
#include <stdio.h>

void main()
{
    char input[100];
    printf("Type a String which will be converted to an Integer: ");
    scanf("%s", input);

    int number = 0;
    int i = 0;
    int x = 0;
    bool success = true;

    while (input[i] != '\0')
    {
        if (input[i] >= '0' && input[i] <= '9')
        {
            number = number * 10 + input[i] - '0';
            i++;
        }
        else
        {
            success = false;
            printf("\n");
            printf("Character %c is not a number! \n", input[i]);
            break;
        }
    }
    if (success)
    {
        printf("string %s -> number %d \n", input, number);
    }
}

A:

If you want to point the first not allowed char.
int main()
{
    char input[100];
    char arrow[100] = {0};
    printf("Type a String which will be converted to an Integer: ");
    scanf("%s", input);

    int number = 0;
    int i = 0;
//    int x = 0;
    bool success = true;

    while (input[i] != '\0')
    {
        if (input[i] >= '0' && input[i] <= '9')
        {
            number = number * 10 + input[i] - '0';
            arrow[i] = ' ';
            i++;
        }
        else
        {
            success = false;
            arrow[i]='^';
            printf("\nInput number is wrong!\n%s\n%s\n", input, arrow);
            break;
        }
    }
    if (success)
    {
        printf("string %s -> number %d \n", input, number);
    }

    return 0;
}

output is
Input number is wrong!
423432rr55
      ^

