Program prints memory address when converting hexadecimal to an integer - c

Question

I have seen other solutions to this problem where a pointer is used. I don't understand the workings of a pointer enough to implement them into this program. If the solution requires one, would someone please be able to explain why? I have been trying various things with this program all night and gotten nowhere. I read the relevant text in 'The C Programming Language' book, where the exercise is from. I can't be the only person stumped by this D:
#include <stdio.h>
#include <math.h>
#include <ctype.h>
#define MAX 1000
int htoi(char s[]);
main()
{
char line[MAX];
int i, c;
printf("Enter the strig to convert to an integer:");
for(i=0; i<MAX && (c=getchar())!=EOF && c != '\n'; ++i)
line[i] = c;
int a =0;
a = htoi(line);
printf("%d", a);
}
int htoi(char s[])
{
int i, n, z;
n=0;
int total = 0;
for(i=0; s[i] != '\0'; ++i)
{
if (s[i] == 'a'||s[i] == 'A')
n = 10;
else if(s[i] == 'b'||s[i] == 'B')
n = 11;
else if(s[i] == 'c'||s[i] == 'C')
n = 12;
else if(s[i] == 'd'||s[i] == 'D')
n = 13;
else if(s[i] == 'e'||s[i] == 'E')
n = 14;
else if(s[i] == 'f'||s[i] == 'F')
n = 15;
else
n = s[i];
z = n * pow(16, i);
total = total + z;
}
return total;
}

Answer 1

Someone correct me if I am wrong. But you're not putting a null terminator in your char array:
for(i=0; i<MAX && (c=getchar())!=EOF && c != '\n'; ++i)
line[i] = c;
Later on, you do
for(i=0; s[i] != '\0'; ++i)
But since you never appended a null terminator the above for loop will iterate PAST the bounds of the array until it sees a null somewhere on the stack or it segfaults.
you should be doing the following:
for(i=0; i<(MAX-1) && (c=getchar())!=EOF && c != '\n'; ++i)
line[i] = c;
line[i+1] = '\0';
Note the (MAX-1)
P.S Don't run anything that doesn't require root as root, see: least privilege principle

Answer 2

Your problem is here:
else
n = s[i]; // <- n is getting the character code value of S[i]
To solve, I suggest to do:
else
n = s[i] - '0';
EDITED:
You have two problems else:
You need to null terminate the line char (your string hasn't '\0')
You are inverting the power math (digit more at left are more significants than at right position)
To solve (1), do that:
for(i=0; i<MAX && (c=getchar())!=EOF && c != '\n'; ++i)
line[i] = c;
line[i] = '\0'; // <-- added here
To solve (2), do that:
int total = 0;
int len = strlen(s) - 1; // <- added here
...
z = n * pow(16, len - i); // <- change here
Another way, you can avoid using the expensive pow function by just shifting 4 bits to left as in code bellow:
instead of:
z = n * pow(16, i);
total = total + z;
do:
total <<= 4; // changed here
total += n; // and here