The 2s complement in C is generated from the 1s complement in C. As we know that the 1s complement of a binary number is created by transforming bit 1 to 0 and 0 to 1; the 2s complement of a binary number is generated by adding one to the 1s complement of a binary number.

In short, we can say that the 2s complement in C is defined as the sum of the one's complement in C and one.

In the above figure, the binary number is equal to 00010100, and its one's complement is calculated by transforming the bit 1 to 0 and 0 to 1 vice versa. Therefore, one's complement becomes 11101011. After calculating one's complement, we calculate the two's complement by adding 1 to the one's complement, and its result is 11101100.

Let's create a program of 2s complement.

snippet

#include <stdio.h> int main() { int n; // variable declaration printf("Enter the number of bits do you want to enter :"); scanf("%d",&n); char binary[n+1]; // binary array declaration; char onescomplement[n+1]; // onescomplement array declaration char twoscomplement[n+1]; // twoscomplement array declaration int carry=1; // variable initialization printf("\nEnter the binary number : "); scanf("%s", binary); printf("%s", binary); printf("\nThe ones complement of the binary number is :"); // Finding onescomplement in C for(int i=0;i<n;i++) { if(binary[i]=='0') onescomplement[i]='1'; else if(binary[i]=='1') onescomplement[i]='0'; } onescomplement[n]='\0'; printf("%s",onescomplement); printf("\nThe twos complement of a binary number is : "); // Finding twoscomplement in C for(int i=n-1; i>=0; i--) { if(onescomplement[i] == '1' && carry == 1) { twoscomplement[i] = '0'; } else if(onescomplement[i] == '0' && carry == 1) { twoscomplement[i] = '1'; carry = 0; } else { twoscomplement[i] = onescomplement[i]; } } twoscomplement[n]='\0'; printf("%s",twoscomplement); return 0; }

**Output**

- First, we input the number of bits, and it gets stored in the '
**n**' variable. - After entering the number of bits, we declare character array, i.e.,
**char binary[n+1],**which holds the binary number. The '**n**' is the number of bits which we entered in the previous step; it basically defines the size of the array. - We declare two more arrays, i.e.,
**onescomplement[n+1]**, and**twoscomplement[n+1].**The**onescomplement[n+1]**array holds the ones complement of a binary number while the**twoscomplement[n+1]**array holds the two's complement of a binary number. - Initialize the
**carry**variable and assign 1 value to this variable. - After declarations, we input the binary number.
- Now, we simply calculate the one's complement of a binary number. To do this, we create a
**loop**that iterates throughout the binary array,**for(int i=0;i<n;i++)**. In for loop, the condition is checked whether the bit is 1 or 0. If the bit is 1 then**onescomplement[i]=0**else**onescomplement[i]=1**. In this way, one's complement of a binary number is generated. - After calculating one's complement, we generate the 2s complement of a binary number. To do this, we create a
**loop**that iterates from the last element to the starting element. In for loop, we have three conditions:- If the bit of onescomplement[i] is 1 and the value of carry is 1 then we put 0 in twocomplement[i].
- If the bit of onescomplement[i] is 0 and the value of carry is 1 then we put 1 in twoscomplement[i] and 0 in carry.
- If the above two conditions are false, then onescomplement[i] is equal to twoscomplement[i].

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