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Question

The following code is supposed to find the largest digit in any given integer.
It almost does it perfectly minus the exception—numbers 10000 or 504030201. What I noticed is, it does not accept the first number of these integers for some odd reason.

Any ideas?

https://code.sololearn.com/c44pFHdg546c/?ref=app

Answer 1

For 10000, the loop in your code results in the following:
i = 0, num = 10000, mod = 0, sum = 0, i < num;
i = 1, num = 1000, mod = 0, sum = 0, i < num;
i = 2, num = 100, mod = 0, sum = 0, i < num;
i = 3, num = 10, mod = 0, sum = 0, i < num;
i = 4, num = 1, i > num;

While the iteration for the last digit (or more if the length of a decimal representation of number is 10 or more) a should also be executed.

How to fix it:
1. Use while loop and not for loop. In the condition write either `num != 0` or `num` (still stops iterationg when the result is 0).
2. Replace the second "condition" part of a for loop with the code mentioned before.
I would recommend to use the first way, as it is more relatable to this case and does not require additional variable.

Answer 2

Use long int that can manage the overflow

#include <stdio.h>

int main(void) {
long int num, i;
int mod, sum=0;

scanf("%li",&num);

for(i=0; i<=num; i++)
{
mod = num % 10;
if(sum<mod)
{
sum = mod;
}
num /= 10;
}
printf("%i",sum);
return 0;
}