Binary String to Signed 8-bit Integer

Task

Implement the function bin8_to_dec

• Write a function that takes a null-terminated char[] consisting of '0' and '1' characters ($\text{length}=8$) and returns the signed 8-bit integer value it represents
• The function signature

// Given a char[8] representing a binary number, returns the signed 8-bit integer it represents
// For example:
//   "10000000" produces -128 (most negative 8-bit number)
//   "00000001" produces 1
//   "00000000" produces 0
//   "11111111" produces -1
//   "01111111" produces 127 (most positive 8-bit number)
int8_t bin8_to_dec(char binary[]);

---

Test

$ gcc bin8_to_dec.c -o bin8_to_dec
$ ./bin8_to_dec
10000000
-128
00000001
1
11111111
-1
$ ./bin8_to_dec < small_input.txt
-128
1
0
127
-1

---

Code

#include <stdint.h>
#include <string.h>
 
int8_t bin8_to_dec(char binary[]){
	int8_t result = 0;
	int8_t value_at_index = 1;
	size_t max_len = strlen(binary);
	
	for(int i = max_len - 1; i > 0; i--, value_at_index *= 2){
		if(binary[i] == '1'){
			result += value_at_index;
		}
	}
	
	if (binary[0] == '1') {result -= 128;}
	return result;
}

NOTE

Signed Integer value uses 2’s Compliment convention, where the most significant bit represents the negative at that value → In an 8-bit integer, the most significant bit is the $2^7=128$, therefore the signed 8-bit integer value at the most significant bit is $-128$