diff --git a/arith/Makefile b/arith/Makefile
index b752a6e..c650405 100644
--- a/arith/Makefile
+++ b/arith/Makefile
@@ -1,4 +1,4 @@
-TARGETS = adder substractor
+TARGETS = adder substractor multiplier divider negator comparator
 
 .PHONY: all clean
 
@@ -10,4 +10,12 @@ clean:
 adder:
 	gcc -I../common/ ../common/auxiliar.c adder.c -o adder 
 substractor:
-	gcc -I../common/ ../common/auxiliar.c substractor.c -o substractor 
\ No newline at end of file
+	gcc -I../common/ ../common/auxiliar.c substractor.c -o substractor 
+multiplier:
+	gcc -I../common/ ../common/auxiliar.c multiplier.c -o multiplier 
+divider:
+	gcc -I../common/ ../common/auxiliar.c divider.c -o divider 
+negator:
+	gcc -I../common/ ../common/auxiliar.c negator.c -o negator
+comparator:
+	gcc -I../common/ ../common/auxiliar.c comparator.c -o comparator
\ No newline at end of file
diff --git a/arith/comparator.c b/arith/comparator.c
new file mode 100644
index 0000000..4b6108f
--- /dev/null
+++ b/arith/comparator.c
@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <string.h>
+#include "auxiliar.h"
+
+int check_length(char **inputs, uint8_t num_inputs)
+{
+	int input_length = strlen(inputs[0]);
+    if(input_length != strlen(inputs[1]))
+    {
+    	return -1;
+    }
+    return input_length;
+}
+
+int main(int argc, char **argv)
+{
+	int i;
+	int pos;
+	if(argc != 2)
+	{
+		error();
+	}
+	char *input = argv[1];
+	if(!strcmp(input,"error"))
+	{
+		error();
+	}
+	char **inputs = comma_separate(input);
+	if(inputs == NULL)
+	{
+		error();
+	}
+	int num_inputs = num_occurrences(input,',');
+	if(num_inputs != 2)
+	{
+		error();
+	}
+	int input_length = check_length(inputs,num_inputs);
+	int a,b;
+	a = bin2dec(inputs[0]);
+	b = bin2dec(inputs[1]);
+	if(a > b)
+	{
+		printf("1,0,0");
+	}
+	else if(a < b)
+	{
+		printf("0,0,1");
+	}
+	else if(a == b)
+	{
+		printf("0,1,0");
+	}
+	free_mem(inputs,num_inputs);
+	return 0;
+}
diff --git a/arith/divider.c b/arith/divider.c
new file mode 100644
index 0000000..163d93f
--- /dev/null
+++ b/arith/divider.c
@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <string.h>
+#include "auxiliar.h"
+
+int check_length(char **inputs, uint8_t num_inputs)
+{
+	int input_length = strlen(inputs[0]);
+	int i;
+	for(i = 1; i < 3; i++)
+	{
+		if(input_length != strlen(inputs[i]))
+		{
+			return -1;
+		}
+	}
+    return input_length;
+}
+
+int main(int argc, char **argv)
+{
+	int i;
+	int pos;
+	if(argc != 2)
+	{
+		error();
+	}
+	char *input = argv[1];
+	if(!strcmp(input,"error"))
+	{
+		error();
+	}
+	char **inputs = comma_separate(input);
+	if(inputs == NULL)
+	{
+		error();
+	}
+	int num_inputs = num_occurrences(input,',');
+	if(num_inputs != 3)
+	{
+		error();
+	}
+	int input_length = check_length(inputs,num_inputs);
+	if(input_length == -1)
+	{
+		error();
+	}
+	int a,b,c,rem;
+	char *upper = inputs[0];
+	char *lower = inputs[1];
+	char *op = (char*) malloc(sizeof(char)*(input_length+1));
+	memset(op,0x00,input_length+1);
+	strcpy(op,upper);
+	strcat(op,lower);
+	a = bin2dec(op);
+	b = bin2dec(inputs[2]);
+	c = a/b;
+	rem = a%b;
+	char *result = dec2bin(c,input_length);
+	char *rem_bin = dec2bin(rem,input_length);
+	printf("%s,%s",result,rem_bin);
+	free(result);
+	free(rem_bin);
+	free(op);
+	free_mem(inputs,num_inputs);
+	return 0;
+}
diff --git a/arith/multiplier.c b/arith/multiplier.c
new file mode 100644
index 0000000..487d40f
--- /dev/null
+++ b/arith/multiplier.c
@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <string.h>
+#include "auxiliar.h"
+
+int check_length(char **inputs, uint8_t num_inputs)
+{
+	int input_length = strlen(inputs[0]);
+	int i;
+	for(i = 1; i < 3; i++)
+	{
+		if(input_length != strlen(inputs[i]))
+		{
+			return -1;
+		}
+	}
+    return input_length;
+}
+
+int main(int argc, char **argv)
+{
+	int i;
+	int pos;
+	if(argc != 2)
+	{
+		error();
+	}
+	char *input = argv[1];
+	if(!strcmp(input,"error"))
+	{
+		error();
+	}
+	char **inputs = comma_separate(input);
+	if(inputs == NULL)
+	{
+		error();
+	}
+	int num_inputs = num_occurrences(input,',');
+	if(num_inputs != 3)
+	{
+		error();
+	}
+	int input_length = check_length(inputs,num_inputs);
+	if(input_length == -1)
+	{
+		error();
+	}
+	int a,b,carry_in,c;
+	a = bin2dec(inputs[0]);
+	b = bin2dec(inputs[1]);
+	carry_in = bin2dec(inputs[2]);
+	c = (a*b)+carry_in;
+	char *result = dec2bin(c,input_length*2);
+	printf("%s,%.*s",result+input_length,input_length,result);
+	free(result);
+	free_mem(inputs,num_inputs);
+	return 0;
+}
diff --git a/arith/negator.c b/arith/negator.c
new file mode 100644
index 0000000..2166863
--- /dev/null
+++ b/arith/negator.c
@@ -0,0 +1,36 @@
+#include <stdio.h>
+#include <string.h>
+#include "auxiliar.h"
+
+int main(int argc, char **argv)
+{
+	int i;
+	int pos;
+	if(argc != 2)
+	{
+		error();
+	}
+	char *input = argv[1];
+	if(!strcmp(input,"error"))
+	{
+		error();
+	}
+	char **inputs = comma_separate(input);
+	if(inputs == NULL)
+	{
+		error();
+	}
+	int num_inputs = num_occurrences(input,',');
+	if(num_inputs != 1)
+	{
+		error();
+	}
+	int input_length = strlen(inputs[0]);
+	int num = bin2dec(inputs[0]);
+	num *= -1;
+	char *result = dec2bin(num,input_length);
+	printf("%s",result);
+	free(result);
+	free_mem(inputs,num_inputs);
+	return 0;
+}
diff --git a/arith/substractor.c b/arith/substractor.c
index f3071a2..a89f120 100644
--- a/arith/substractor.c
+++ b/arith/substractor.c
@@ -14,7 +14,7 @@ int check_length(char **inputs, uint8_t num_inputs)
 
 int main(int argc, char **argv)
 {
-	/*int i;
+	int i;
 	int pos;
 	if(argc != 2)
 	{
@@ -54,7 +54,5 @@ int main(int argc, char **argv)
 	printf("%s,%c",result,borrow_out);
 	free(result);
 	free_mem(inputs,num_inputs);
-	return 0;*/
-	printf("%d",bin2dec("11000000"));
 	return 0;
 }
diff --git a/common/auxiliar.c b/common/auxiliar.c
index b6cb383..c2faea2 100644
--- a/common/auxiliar.c
+++ b/common/auxiliar.c
@@ -60,7 +60,7 @@ char** comma_separate(char *input)
                 return NULL;
         }
         char **inputs;
-        inputs = malloc(sizeof(char*) * (input_num+1));
+        inputs = (char**) malloc(sizeof(char*) * (input_num+1));
         for(i = 0; i < input_num; i++)
         {
                 next_pos += next_occurrence(input+pos,',');
@@ -130,6 +130,7 @@ int bin2dec(char *bin)
         int length = strlen(bin);
         int pos = length - 1;
         char *aux = (char*) malloc(sizeof(char) * (length+1));
+        memset(aux,0x00,length+1);
         strcpy(aux,bin);
         if(aux[0] == '1')
         {       
@@ -152,6 +153,7 @@ int bin2dec(char *bin)
 char* dec2bin(int dec, int length)
 {
         char *bin = (char*) malloc(sizeof(char) * (length + 1));
+        memset(bin,0x00,length+1);
         int pos = length-1;
         int i;
         for(i = 0; i < length; i++)
@@ -172,7 +174,8 @@ char* dec2bin(int dec, int length)
 
 void expand_input(char **input, int required_length)
 {
-        char *new_input = malloc(sizeof(char)*(required_length + 1));
+        char *new_input = (char*) malloc(sizeof(char)*(required_length + 1));
+        memset(new_input,0x00,required_length + 1);
         memset(new_input,'0',required_length+1);
         int offset = required_length - strlen(*input);
         strcpy(new_input + offset,*input);
diff --git a/logic_gate/logic_gate.c b/logic_gate/logic_gate.c
index d82fae4..862be8e 100644
--- a/logic_gate/logic_gate.c
+++ b/logic_gate/logic_gate.c
@@ -21,7 +21,7 @@ char* or(char **inputs, int num_inputs, int input_length)
 {
 	int i;
 	int j;
-	char *result = malloc(sizeof(char) * (input_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (input_length + 1));
 	memset(result, 0x00, input_length+1);
 	for(i = 0; i < input_length; i++)
 	{
@@ -46,7 +46,7 @@ char* nor(char **inputs, int num_inputs, int input_length)
 {
 	int i;
 	int j;
-	char *result = malloc(sizeof(char) * (input_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (input_length + 1));
 	memset(result, 0x00, input_length+1);
 	for(i = 0; i < input_length; i++)
 	{
@@ -71,7 +71,7 @@ char* xor(char **inputs, int num_inputs, int input_length)
 {
 	int i;
 	int j;
-	char *result = malloc(sizeof(char) * (input_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (input_length + 1));
 	memset(result, 0x00, input_length+1);
 	for(i = 0; i < input_length; i++)
 	{
@@ -95,7 +95,7 @@ char* xnor(char **inputs, int num_inputs, int input_length)
 {
 	int i;
 	int j;
-	char *result = malloc(sizeof(char) * (input_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (input_length + 1));
 	memset(result, 0x00, input_length+1);
 	for(i = 0; i < input_length; i++)
 	{
@@ -119,7 +119,7 @@ char* and(char **inputs, int num_inputs, int input_length)
 {
 	int i;
 	int j;
-	char *result = malloc(sizeof(char) * (input_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (input_length + 1));
 	memset(result, 0x01, input_length+1);
 	for(i = 0; i < input_length; i++)
 	{
@@ -143,7 +143,7 @@ char* nand(char **inputs, int num_inputs, int input_length)
 {
 	int i;
 	int j;
-	char *result = malloc(sizeof(char) * (input_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (input_length + 1));
 	memset(result, 0x01, input_length+1);
 	for(i = 0; i < input_length; i++)
 	{
@@ -167,7 +167,7 @@ char* not(char **inputs, int num_inputs, int input_length)
 {
 	int i;
 	int j;
-	char *result = malloc(sizeof(char) * (input_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (input_length + 1));
 	memset(result, 0x01, input_length+1);
 	for(i = 0; i < input_length; i++)
 	{
diff --git a/plexers/bit_selector.c b/plexers/bit_selector.c
index 44b8285..ad48c45 100644
--- a/plexers/bit_selector.c
+++ b/plexers/bit_selector.c
@@ -56,7 +56,7 @@ int main(int argc, char **argv)
 	{
 		expand_input(&inputs[0],required_length);
 	}
-	char *result = malloc(sizeof(char) * (output_length + 1));
+	char *result = (char*) malloc(sizeof(char) * (output_length + 1));
 	memset(result,0x00,output_length+1);
 	int selected = bin2dec(inputs[1]);
 	int pos = 0;
diff --git a/todo b/todo
index c593e23..960bb4f 100644
--- a/todo
+++ b/todo
@@ -1,9 +1,3 @@
-adder
-substractor
-multiplier
-divider
-negator
-comparator
 shifter
 bit adder
 bit finder