Using the character array as integers - c

Question

Hello Guys I am trying to solve one problem given on the Hacker Rank. Though the problem is quite simple, I was thinking to solve the problem using some other concepts.
The problem is
Desription
You are given an integer N. Find the digits in this number that exactly divide N (division that leaves 0 as remainder) and display their count. For N=24, there are 2 digits (2 & 4). Both of these digits exactly divide 24. So our answer is 2.
Input Format
The first line contains T (the number of test cases), followed by T lines (each containing an integer N).
Constraints
1≤T≤15
0
I solved the problem earlier by defining variable N as of type long long but that i guess will not be the efficient way to solve the problem.
So i thought why not declare the variable N as an character array. This way we can also use the program to store the number greater then the max limit of long long also rt?
Say i used the following code
#include <stdio.h>
#include <string.h>
int main()
{
int i,t;
char n[20];
scanf("%d",&t);
while(t--)
{
scanf("%s",n);
int len=strlen(n);
int f2,f3,f5,f7,f4,count;
f2=f3=f5=f7=f4=count=0;
for( i=0;i<len;++i)
{ int sum=0;
switch((int)n[i])
{
case 48: break;
case 49: ++count;break;
case 50: if((int)n[len-1]%2==0) // divisibility by 2
{
++count;f2=1;
}break;
case 51: for(i=0;n[i]!='\0';++i) // divisibility by 3
{
sum+=(int)n[i];
}
if(sum%3==0)
{
++count;
f3=1;
}break;
case 52: if(f2==1) // divisibility by 4
{
++count;
f4=1;
} break;
case 53: if(n[len-1]=='5' || n[len-1]=='0') // divisibility by 5
{
++count;
f5=1;
}break;
case 54: if(f2==1 && f3==1) // divisibility by 6
{
++count;
break;
}
case 55: // Code for divisibilty by 7
case 56: if(f2==1 && f4==1) // divisibility by 8
{ ++count;
break;
}
case 57: if(f3==1) // divisibility by 9
{
++count;
break;
}
}
}
printf("%d\n",count);
}
return 0;
}
The program is working fine but the only problem is I am not able to rt the code for divisibility by 7 anu suggestions will be helpful, And also which is the better way to solve the problem , This way in which the variable N is declared as the character array or by declaring the variable N as long long.
Any improvements for the above code would also be appreciated .....:)

Answer 1

Divisibility by 7 can be checked by this rule
Also you can use this mod() function to check divisibility by any number :
int mod(char *n, int val)
{
int sum = 0;
for(int i=0; n[i]; i++)
{
sum = sum*10 + (n[i]-'0');
if(sum >= val)
sum = sum % val;
}
return sum;
}
it will return 0, if the number n is divisible by number val :)
And you don't need to check for every redundant digit.
First check the available digit then check for divisibility once for each digit.
Here's what you can do -
#include <stdio.h>
#include <string.h>
int mod(char *n, int val)
{
int sum = 0;
for(int i=0; n[i]; i++)
{
sum = sum*10 + (n[i]-'0');
if(sum >= val)
sum = sum % val;
}
return sum;
}
int main()
{
int i,t;
int digit[10];
char n[20];
scanf("%d",&t);
while(t--)
{
scanf("%s",n);
int len=strlen(n);
int cnt=0;
memset(digit,0,sizeof(digit)); // setting all the digit to 0
for(i=0;i<len;i++)
digit[n[i]-'0']++;
for(i=1;i<10;i++)
{
if(digit[i]==0) // number doesn't contain any of this digit
continue;
if(mod(n,i)==0)
cnt+=digit[i]; // Adding the digit to the answer
}
printf("%d\n",cnt);
}
return 0;
}
How this works :
for n = 147 and val = 7
sum = 0
1st iter >> sum = 0*10 + 1 = 1
sum < val, so continue
2nd iter >> sum = 1*10 + 4 = 14
sum >= val, so sum = sum % val = 14 % 7 = 0
3rd iter >> sum = 0*10 + 7 = 7
sum >= val, so sum = sum % val = 7 % 7 = 0
as the final sum is 0, so we can say that n is divisible by val :)