Program keeps spamming numbers? - c++

Question

#include <iostream>
using namespace std;
int main(){
int a;
int b;
int dif;
cout<<"insert a: "<<endl;
cin>>a;
cout<<"insert b: "<<endl;
cin>>b;
if(a>b){
while(dif>=3){
dif=a-b;
cout<<dif;
}
}else{
while(dif>=3){
dif=b-a;
cout<<dif;
}
}
}
This is supposed to be a program that reads two numbers and keeps subtracting the smaller one from the bigger one until the difference is < 3 units. While it does this it should also output the difference at every iteration and for some reason it spams the difference or doesnt output anything. Help?

Answer 1

Two problems in your while loops:
while(dif>=3){
dif=a-b;
cout<<dif;
}
First, dif is used uninitialized and using it will cause undefined behavior. After you fix that the loop will still not do what you want.
dif=a-b; will assign to dif the same value in every iteration, hence the loop will run either never (condition is false before the loop), once (condition is false after the assignment), or forever (condition is still true after the assignment). I suppose this isn't the intended behavior.
...and keeps subtracting the smaller one from the bigger one until the difference is < 3 units.
You forgot to actually subtract one number from the other. That would be (in case a is the bigger):
while ( a-b >= 3) a -= b;
or with an additional variable (I don't think it helps, but rather adds complexity):
int diff = a-b;
while (diff >= 3) {
a -= b;
diff = a-b;
}

Answer 2

You need to initialize dif to be a number, e.g. int dif = 0;. C++ doesn't say what happens when you manipulate or use an uninitialized variable, so anything can happen and your program won't work consistently- this is probably why you've had it produce no output. This phenomenon is known as undefined behavior- see here for a full explanation.
Additionally, your loops also go infinite- if a is greater than b, dif >=3, and you set dif = a - b, dif is always the same, so the condition will always be true, and thus your code never stops running. You need to subtract and reassign the variable first so the values change, and then update dif:
a = a - b
dif = a - b
The second loop has the same problem.

Answer 3

There are two issue here ..
diff is not assigned any default value so it gets random value, if it will be greater or equal than 3 it will print infinity and if it is less than it will do nothing.
initiaalize the diff with diff=abs(b-a)
if by chance diff enter the loop then on every iteration diff is not changing as a and b remain same. So change the logic.
Instead of if else and two while loops just use diff=abs(b-a)
Good Luck