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Problem Solving

caution

https://youtu.be/QDFM7Mjk2mc?t=1965

https://www.geeksforgeeks.org/why-global-array-has-a-larger-size-than-the-local-array/

declaring inside main()declaring OUTSIDE main() [Global Variables]........
bool107108
double
long long
long double

When to use Global Variables​

Use global Variables wherever you can

by CONSTANT I mean variabled declared above main()

  • if lets say I have to find prime numbers till n, then I can declare the is_prime from [Sieve of Eratosthenes] as a CONSTANT decalred before main(). By this will have a bool array with all prime numbers lesss than given contraint such as 106. So this will be inside a method of Time Complexity O(n.log(log n)).
    • IF I did it without a declaring is_prime vector of type bool as CONSTANT then I would have to make this bool vector for each given test case, here the no. of test cases are 105. Then the method for creating the is_prime bool vector with primes true will be insite the test case loop while(t--). So the Time Complexity will become O(T*n.log(log n))

Eat up a unnecessary string or char​

Below program takes input 12/78 as fraction and then char ignore takes in the / fraction divider and thus other variables can take up required integer values

#include <iostream>

int main()
{
    // Our first fraction
    int num1 {};
    int den1 {};

    // Our second fraction
    int num2 {};
    int den2 {};

    // Used to eat the slash between the numerator and denominator
    char ignore {};

   cout << "Enter a fraction: ";
   cin >> num1 >> ignore >> den1;

   cout << "Enter a fraction: ";
   cin >> num2 >> ignore >> den2;

   cout << "The two fractions multiplied: "
        << num1 * num2 << '/' << den1 * den2 << '\n';

    return 0;
}

DRY (don’t repeat yourself) principle​

  • if some operations are done repetitively then we must create a funtion() to do it.