C program for binary addition/subtraction using two's complement

1 Pseudocode:

1.      Start
2.      Ask user to enter choice
3.      Clear all variables
4.      Call ‘add’ function if addition, otherwise ‘sub’ function
5.      Continue until user wants
6.      End

Add function:

1.      Start
2.      Ask user to enter two 8-bit numbers: num1, num2
3.      carry = 0
4.      Begin Addition from LSB
5.      sum = num1[i] + num2[i] + carry
6.      If sum of two bits >= 2, carry = 1
7.      Otherwise, carry = 0
8.      sum = sum % 2
9.      Repeat 5 through 8 until all bits are added
10.  Display sum
11.  End

Sub function:

1.      Start
2.      Ask user to enter two 8-bit numbers: num1, num2
3.      Begin Addition from LSB
4.      diff = num1[i] – num2[i]
5.      If difference of two bits < 0, num1[i-1] = num1[i-1] - 1
6.      diff = absolute(diff % 2)
7.      Repeat 5 through 7 until all bits are added
8.      Display diff
9.      End

2 Program:

#include <stdio.h>

#include <conio.h>

#include <math.h>

int c = 0,numa[8]={0},numb[8]={0},diff[8]={0},sum[8]={0};

void add();

void sub();

void main(){

            int ch;

            do{

            clrscr();

            for(int i=0; i<8; i++){

                        numa[i] = 0;

                        numb[i] = 0;

                        diff[i] = 0;

                        sum[i] = 0;

            }

            c = 0;

            printf("\tADDITION-SUBTRACTION USING TWO'S COMPLEMENT");

            printf("\n1.ADD\n2.SUBTRACT\nEnter your choice: ");

            scanf("%d",&ch);

                        switch(ch){

                                    case 1: add();

                                                break;

                                    case 2: sub();

                                                break;

                                    default: printf("\nInvalid Choice: ");

                        }

            printf("\nPress 1 to Continue...");

            scanf("%d",&ch);

            }while(ch == 1);

}

void add(){

            printf("\nEnter two 8-bit binary numbers\n");

            printf("\nEnter first number: ");

            for(int i = 0; i<8; i++){

                        scanf("%d",&numa[i]);

            }

            printf("\nEnter second number: ");

            for(i = 0; i<8; i++){

                        scanf("%d",&numb[i]);

            }

            for(i = 7; i >= 0; i--){

                        sum[i] = numa[i]+ numb[i] + c;

                        if(sum[i]>=2){

                                    c = 1;

                        }

                        else

                                    c = 0;

                        sum[i] = sum[i]%2;

            }

            printf("\nSum is: ");

            for(i = 0; i<8; i++){

                        printf("%d",sum[i]);

            }

}

void sub(){

            printf("\nEnter two 8-bit binary numbers\n");

            printf("\nEnter first number: ");

            for(int i = 0; i<8; i++){

                        scanf("%d",&numa[i]);

            }

            printf("\nEnter second number: ");

            for(i = 0; i<8; i++){

                        scanf("%d",&numb[i]);

            }

            for(i = 7; i >= 0; i--){

                        diff[i] = numa[i] - numb[i];

                        if(diff[i] < 0){

                                    numa[i-1] = numa[i-1] - 1;

                        }

                        diff[i] = fabs(diff[i]%2);

            }

            printf("\nDifference is: ");

            for(i = 0; i<8; i++){

                        printf("%d",diff[i]);

            }

}

©Dixit Bhatta 2013