Global and local variables - c++

Question

I was just wondering why playerHp doesn't stay at it's value but resets to 30 each time I call the function. Is it because the variable is local, and if so how do I make it go global from within the function?
I'm new to programming so easy explanations would be nice.
I'm also aware this is "spaghetti code", but if you have the time and energy, cleaning it up would be much appreciated.
#include <iostream>
#include <string>
#include <cstdlib>
//RETURN CODES 1=WON 2=RAN AWAY 3=SLAIN 4=globalWin 5=GlobalLose
using namespace std;
int playerHp;
int enemyHp;
string enemyName;
int dmg()
{
int modifier = rand() % 10 ; // 0-9
return 15 + modifier;
}
int playerDmg()
{
int modifier1 = rand() % 10 ; // 0-9
return 15 + modifier1;
}
int enemyDmg()
{
int modifier2 = rand() % 10 ; // 0-9
return 10 + modifier2;
}
int fight(int playerHp, int enemyHp, string enemyName)
{
int constwhile = 1;
string input;
cout << "You encountered a ";
cout << enemyName <<"\n";
while (constwhile = 1) {
cout << "What will you do?\n";
cout << "Options Fight or Flee: " << flush;
cin >> input;
cin.ignore();
cin.get();
if (input == "Fight" || input == "fight") {
int damageDone = playerDmg();
int finalEnemyHp = enemyHp - damageDone;
cout << "You did ";
cout << damageDone;
cout << " damage" << "\n";
enemyHp = finalEnemyHp;
if (enemyHp < 0) {
cout << "Congratulations! You won!"<<"\n";
return 1;
}
cout << "The monster now has ";
cout << enemyHp;
cout << " health"<<"\n";
} else if (input == "Flee" || input == "flee") {
cout << "You ran away...";
return 2;
} else {
cout<<"Invalid Input"<<"\n";
}
cout << "The enemy fights back!"<< "\n";
int damageDone = enemyDmg();
int finalPlayerHp = playerHp - damageDone;
cout << "It did ";
cout << damageDone;
cout << " damage" << "\n";
playerHp = finalPlayerHp;
if (playerHp < 0) {
cout << "You have been slain...";
return 3;
}
cout << "You now have ";
cout << playerHp;
cout << " health"<<"\n";
}
}
int main()
{
int playerHp = 30;
while(playerHp > 1) {
int fightOutcome = fight(playerHp, rand() % 30, "monster");
if (fightOutcome == 3) {
return 5;
} else if (fightOutcome == 2) {
return 5;
}
}
return 4;
}

Answer 1

The problem are that your global variable are shadow by local defined on function
int fight(int playerHp, int enemyHp, string enemyName)
A fast way to fix your problem is to pass the variables as reference if you want yo keep the value assigned inside function fight
int fight(int &playerHp, int &enemyHp, string &enemyName)

Answer 2

If you want to use a global variable, there must be no local variable or parameter with the same name.
The following will always change the local variable:
int myVar = 0;
void foo(int myVar)
{
myVar = 100;
}
int main()
{
foo(myVar);
cout << myVar;//0
return 0;
}
Now you could either accept a pointer instead of a value, or you could remove the parameter entirely. But I don't really like global pollution, so I would prefer the pointer:
with pointer:
int myVar = 0;
void foo(int* myVar)
{
*myVar = 100;
}
int main()
{
foo(&myVar);
cout << myVar;//100
return 0;
}
without pointer:
int myVar = 0;
void foo()
{
myVar = 100;
}
int main()
{
foo(myVar);
cout << myVar;//100
return 0;
}