problem combining bignum library with bubble sort - c++

Question

From this post: Compare two string as numeric value
I did not get a result.
Please open this post so that someone can answer my question.
I wrote this library (pr.h):
#include <iostream>
#include <string>
#include <bits/stdc++.h>
using namespace std;
class BigNum {
private:
string doSum(string a, string b)
{
if(a.size() < b.size())
swap(a, b);
int j = a.size()-1;
for(int i=b.size()-1; i>=0; i--, j--)
a[j]+=(b[i]-'0');
for(int i=a.size()-1; i>0; i--)
{
if(a[i] > '9')
{
int d = a[i]-'0';
a[i-1] = ((a[i-1]-'0') + d/10) + '0';
a[i] = (d%10)+'0';
}
}
if(a[0] > '9')
{
string k;
k+=a[0];
a[0] = ((a[0]-'0')%10)+'0';
k[0] = ((k[0]-'0')/10)+'0';
a = k+a;
}
return a;
}
bool isSmaller(string str1, string str2)
{
int n1 = str1.length(), n2 = str2.length();
if (n1 < n2)
return true;
if (n2 < n1)
return false;
for (int i = 0; i < n1; i++) {
if (str1[i] < str2[i])
return true;
else if (str1[i] > str2[i])
return false;
}
return false;
}
string findDiff(string str1, string str2)
{
if (isSmaller(str1, str2))
swap(str1, str2);
string str = "";
int n1 = str1.length(), n2 = str2.length();
int diff = n1 - n2;
int carry = 0;
for (int i = n2 - 1; i >= 0; i--) {
int sub = ((str1[i + diff] - '0') - (str2[i] - '0')
- carry);
if (sub < 0) {
sub = sub + 10;
carry = 1;
}
else
carry = 0;
str.push_back(sub + '0');
}
for (int i = n1 - n2 - 1; i >= 0; i--) {
if (str1[i] == '0' && carry) {
str.push_back('9');
continue;
}
int sub = ((str1[i] - '0') - carry);
if (i > 0 || sub > 0)
str.push_back(sub + '0');
carry = 0;
}
reverse(str.begin(), str.end());
return str;
}
public:
string num;
BigNum () {
num = "";
}
BigNum (string tmp) {
num = tmp;
}
string operator +(BigNum a1) {
return doSum(this->num,a1.num);
}
void operator = (BigNum * a1) {
this-> num = a1-> num;
}
void operator = (string tmp) {
this-> num = tmp;
}
bool operator > (BigNum a1) {
if (this->num>a1.num){
return true;
}
else{
return false;
}
}
bool operator < (BigNum a1) {
if (this->num<a1.num){
return true;
}
else{
return false;
}
}
string operator - (BigNum a1) {
return findDiff(this->num, a1.num);
}
friend ostream &operator<<( ostream &output, const BigNum &D ) {
output << D.num;
return output;
}
friend istream &operator>>( istream &input, BigNum &D ) {
input >> D.num;
return input;
}
string operator -=(string tmp){
this->num=findDiff(this->num, tmp);
return this->num;
}
};
And this code:
// C++ program for implementation of Bubble sort
#include "pr.h"
#include <bits/stdc++.h>
using namespace std;
void swap(BigNum *xp, BigNum *yp)
{
BigNum temp = *xp;
*xp = *yp;
*yp = temp;
}
// A function to implement bubble sort
void bubbleSort(BigNum arr[], int n)
{
int i, j;
for (i = 0; i < n-1; i++)
// Last i elements are already in place
for (j = 0; j < n-i-1; j++)
if (arr[j] > arr[j+1])
swap(&arr[j], &arr[j+1]);
}
/* Function to print an array */
void printArray(BigNum arr[], int size)
{
int i;
for (i = 0; i < size; i++)
cout << arr[i] << " ";
cout << endl;
}
// Driver code
int main()
{
BigNum arr[5];
arr[0]="5";
arr[1]="5";
arr[2]="1";
arr[3]="3";
arr[4]="8";
int n = sizeof(arr)/sizeof(arr[0]);
bubbleSort(arr, n);
cout<<"Sorted array: \n";
printArray(arr, n);
return 0;
}
My problem is that this program can only sort 1-digit numbers and gives errors for multi-digit numbers
Example:
This code:
BigNum arr [5];
arr [0] = "100";
arr [1] = "5";
arr [2] = "1";
arr [3] = "3";
arr [4] = "8";
int n = sizeof (arr) / sizeof (arr [0]);
bubbleSort (arr, n);
cout << "Sorted array: \ n";
printArray (arr, n);
Prints this value:
1 100 3 5 8

Answer 1

bool operator < (BigNum a1) is calling std::string:: operator<, thus you getting lexicographical order. The operators < and > should call isSmaller.
bool operator > (const BigNum& a1) const {
return !isSmaller(a1) && num != a1.num;
}
bool operator < (const BigNum& a1) const {
return isSmaller(a1);
}
Do not use constructions
if (smth) return true else return false. You already get true or false in smth, use return smth.