The two’s complement for a given binary number can be calculated in two methods, which are as follows −
Method 1 − Convert the given binary number into one’s complement and then, add 1.
Method 2 − The trailing zero’s after the first bit set from the Least Significant Bit (LSB) including one that remains unchanged and remaining all should be complementing.
The logic to find two’s complement for a given binary number is as follows −
for(i = SIZE - 1; i >= 0; i--){
if(one[i] == '1' && carry == 1){
two[i] = '0';
}
else if(one[i] == '0' && carry == 1){
two[i] = '1';
carry = 0;
} else {
two[i] = one[i];
}
}
two[SIZE] = '\0';
printf("Two's complement of binary number %s is %s\n",num, two);The logic for finding one’s complement from a given binary number is −
for(i = 0; i < SIZE; i++){
if(num[i] == '0'){
one[i] = '1';
}
else if(num[i] == '1'){
one[i] = '0';
}
}
one[SIZE] = '\0';
printf("Ones' complement of binary number %s is %s\n",num, one);Example
Following is the C program to find two’s complement for a given number −
#include<stdio.h>
#include<stdlib.h>
#define SIZE 8
int main(){
int i, carry = 1;
char num[SIZE + 1], one[SIZE + 1], two[SIZE + 1];
printf("Enter the binary number\n");
gets(num);
for(i = 0; i < SIZE; i++){
if(num[i] == '0'){
one[i] = '1';
}
else if(num[i] == '1'){
one[i] = '0';
}
}
one[SIZE] = '\0';
printf("Ones' complement of binary number %s is %s\n",num, one);
for(i = SIZE - 1; i >= 0; i--){
if(one[i] == '1' && carry == 1){
two[i] = '0';
}
else if(one[i] == '0' && carry == 1){
two[i] = '1';
carry = 0;
}
else{
two[i] = one[i];
}
}
two[SIZE] = '\0';
printf("Two's complement of binary number %s is %s\n",num, two);
return 0;
}Output
When the above program is executed, it produces the following result −
Enter the binary number 1000010 Ones' complement of binary number 1000010 is 0111101 Two's complement of binary number 1000010 is 0111110