Member Avatar for jacline

Hi to all, I have a homework about a banking system. I try to adding a branch in an array and the size of array dynamically increased. Here is my code but it gives run time error.

#include "BankingSystem.h"
#include "Branch.h"
#include <iostream>
using namespace std;
BankingSystem::BankingSystem(){
    size=0;
    branches=NULL;
}

void BankingSystem:: addBranch( const int branchId, const string branchName ){
    Branch b= Branch(branchId, branchName);
    if(size==0){
        size++;
        branches=new Branch[size];
        branches[0]=b;
        cout <<"Branch "<< b.getBranchId()<< " has been added."<<endl;
    }
    else{
        for(int i=0;i<size;i++)
            if(branches[i].getBranchId()==b.getBranchId()){
                cout<<"Branch "<<b.getBranchId()<<" already exists."<<endl;
                return;
            }
        int newsize= size++;
        Branch *temp=new Branch[newsize];
        for(int i=0;i<size;i++){
            temp[i]=branches[i];
        }
        temp[size]=b;
        
        cout <<"Branch "<< b.getBranchId()<< " has been added."<<endl;
        delete[] branches;
        branches=temp;

    }
}
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  • Latest Post Latest Post by jacline

Dani AI

Generated

You are hitting a classic reallocation bug: you must not change size until after you successfully allocate the larger array and copy the existing elements. Keep the old count in a separate variable, copy exactly that many items, append at the old tail index, then swap pointers and update size. This preserves invariants and avoids off-by-one reads/writes. Also, only mutate state after all allocations succeed to keep strong exception safety.

Example reallocation pattern:

void BankingSystem::addBranch(int id, const std::string& name) {
    // check for duplicate id first (linear scan over current size)
    int oldSize = size;
    Branch* next = new Branch[oldSize + 1];
    for (int i = 0; i < oldSize; ++i) next[i] = branches[i];
    next[oldSize] = Branch(id, name);  // append at old tail
    delete[] branches;
    branches = next;
    size = oldSize + 1;
}

Two design cautions:

  • Manage copying properly. If BankingSystem owns a dynamic array, implement the Rule of Three/Five (copy ctor, copy assignment, destructor) or make the type non-copyable. See Rule of three/five/zero.
  • Prefer RAII containers to avoid manual memory errors and quadratic growth. A std::vector<Branch> simplifies this greatly, and a std::unordered_map<int, Branch> makes duplicate checks O(1). See std::vector and std::unordered_map.

Recommended Answers

All 2 Replies

Member Avatar for pecet 
int newsize= size++;
        Branch *temp=new Branch[newsize];
        for(int i=0;i<size;i++){
            temp[i]=branches[i];
        }
        temp[size]=b;

Let's say size is 10. So newsize is also 10. Then you increase size and now size=11. So your loop goes from 0 to 10. But temp[10] doesnt exist. Also temp (which is temp[11] in this example) doesnt exist.

Edited by pecet because: n/a
Member Avatar for jacline 
int newsize= size++;
        Branch *temp=new Branch[newsize];
        for(int i=0;i<size;i++){
            temp[i]=branches[i];
        }
        temp[size]=b;

Let's say size is 10. So newsize is also 10. Then you increase size and now size=11. So your loop goes from 0 to 10. But temp[10] doesnt exist. Also temp (which is temp[11] in this example) doesnt exist.

thanks for your help, but my fault is not same as your saying.yes lets assume size is 10 and with loop I copied the elements from the branches array to temp array which size is 11.(newsize is eleven) .then I say temp (which is temp[10] so it exist) I solved this problem by saying

int newsize=size+1;

and I update size by saying

size=newsize;
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