Friday, 10 May 2013

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

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