Adding hex values from char input in c

Question

I have to make a program that takes the char input from a file, generates their hex value and adds their hex values together (8 bit checksum).

Input:

while(fscanf(ifp, "%c", buffer) != EOF)
{
    input[i] = *buffer;

    printf("%02x", input[i]);
    i++;
}

For example, if the input is "a", the initialoutput should be : 610a (0a for new line char) After adding those together you get 6b. And with "aa" the initial output should be : 61610a and "cc" as result of the addition.

So far I have made a program that reads in char-by-char and stores it. Then I made a recursive function to add the characters together

char addChar(char *input, int i, int size ) {
   if( i == size ) {
      return 0;
   }
   return input[i] + addChar(input, i+1, size);
}

and then I print.

printf("%02x\n", addChar(input, i, size)));

But when I run the program i keep getting a bunch of f's in front of some of the output. I know that is the overflow from adding them together but how do I get rid of that.

Input: a, aa, aaa, aaaa, aaaaa

[Terminal Output][1]

MacbookPro:CheckSum $ ./a.out i1.txt 8

610a

6b

MacbookPro:CheckSum $ ./a.out i2.txt 8

61610a

ffffffcc

MacbookPro:CheckSum $ ./a.out i3.txt 8

6161610a

2d

MacbookPro:CheckSum $ ./a.out i4.txt 8

616161610a

ffffff8e

MacbookPro:CheckSum $ ./a.out i5.txt 8

61616161610a

ffffffef

Show a minimal, complete example program.

Shawn
– Shawn

2018-11-04 20:41:32 +00:00
Commented Nov 4, 2018 at 20:41 — Shawn
– Shawn, Commented Nov 4, 2018 at 20:41
use unsigned char addChar(char *input, int i, int size )

EsmaeelE
– EsmaeelE

2018-11-04 20:59:39 +00:00
Commented Nov 4, 2018 at 20:59 — EsmaeelE
– EsmaeelE, Commented Nov 4, 2018 at 20:59
post complete code include main() function

EsmaeelE
– EsmaeelE

2018-11-04 21:00:18 +00:00
Commented Nov 4, 2018 at 21:00 — EsmaeelE
– EsmaeelE, Commented Nov 4, 2018 at 21:00
Changing it to unsigned char fixed the issue.

CS146R
– CS146R

2018-11-04 22:36:23 +00:00
Commented Nov 4, 2018 at 22:36 — CS146R
– CS146R, Commented Nov 4, 2018 at 22:36

Aubin · Accepted Answer · 2018-11-04 20:41:33Z

1

Try this:

#include <stdio.h>
#include <string.h>

unsigned char addChar( const unsigned char * input, size_t i, size_t size ) {
   if( i == size ) {
      return 0;
   }
   return input[i] + addChar( input, i+1, size );
}

int main( int argc, char * argv[] ) {
   {
      unsigned char input[] = { 'a', '\n' };
      printf( "a    : %02x\n", addChar( input, 0, sizeof( input )));
   }
   {
      unsigned char input[] = { 'a', 'a', '\n' };
      printf( "aa   : %02x\n", addChar( input, 0, sizeof( input )));
   }
   {
      unsigned char input[] = { 'a', 'a', 'a', '\n' };
      printf( "aaa  : %02x\n", addChar( input, 0, sizeof( input )));
   }
   {
      unsigned char input[] = { 'a', 'a', 'a', 'a', '\n' };
      printf( "aaaa : %02x\n", addChar( input, 0, sizeof( input )));
   }
   {
      unsigned char input[] = { 'a', 'a', 'a', 'a', 'a', '\n' };
      printf( "aaaaa: %02x\n", addChar( input, 0, sizeof( input )));
   }
   (void)argc;
   (void)argv;
   return 0;
}

The output:

a    : 6b
aa   : cc
aaa  : 2d
aaaa : 8e
aaaaa: ef

answered Nov 4, 2018 at 20:41

Aubin

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2 Comments

CS146R Over a year ago

This definitely helps me understand little bit more but the im reading in from a txt file from the cmd line so it will not always be a , aa, aaa, etc. So would I just remove the line before the print statement and continue as normal? I am updating the original post to show where im reading in the input.

CS146R Over a year ago

Actually this worked perfectly. the only thing I had to change to my original code was the function. I had it returning a char instead of unsigned char. as well I was assigning the input to char instead of unsigned char. thank you so much!

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