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When we implement add function by operator + in C++, sometimes we face over error - actually system does not show any error and that should be continuously increased, but there is a possibility to change into minus value suddenly. You can see the same case when you compile and run by below code:

#include <iostream>
using namespace std;

int main()
        int a;
        for(int b=0; b<1000000; b++) {
                cout << a << "\n";
                a+= 10000000;

Below safe_add() function enables you to check overflow error:

#define INT_MAX 2147483647
#define INT_MIN -2147483648

    int safe_add(int &sum, int a, int b) {
        if (abs(a)>INT_MAX-abs(b)) {
            cout << "overflow : " << a << "+" << b << endl;
            return 0;
        sum = a + b;
        return 1;

Time Complexity : O(1)
Space Complexity: O(1)