Thread: declaring and intilizing w/in functions

When declaring and initilizing variables: if we put it in the function it would reinitilize it each time the function is called... but also if in main or before main when the function is 'implemented' doesn't seem to work either.

I get "Debug Error!
Run-Time Check Failure #3 - The variable 'j' is being used without being initilized."

Code:

// INCLUDES AND NAMESPACES
#include <iostream>
#include <iomanip>
using namespace std;
 
// PROTOTYPES
int FibonacciIterative(int);
int FibonacciRecursive(int);
 
// MAIN
int main() {
    int i = 0;
    int j = 0;
    int k = 1;
    int l = 1;
    
    for (int i = 0; i < 20; i++) {
        cout << i << '\t';
        FibonacciIterative(i);
        FibonacciRecursive(i);
        cout << '\nl';
    }


    cout << "test output";


    return 0;
}
 
// FUNCTION IMPLEMENTATIONS
// returns F_i of the Fibonacci sequence (iterative)
int FibonacciIterative(int i) {


    int j;
    int k;
    int l;


    if (i == 0) {
        j = 0;
        k = 1;
        l = 1;
        cout << j << '\t';
    }


    l = j + k;
    j = k;
    k = l;
    cout << l << '\t';
    return l;
        


}
 
// returns F_i of the Fibonacci sequence (recursive)
int FibonacciRecursive(int i) {
    cout << "test output two";
    return i;
}

Originally Posted by grumpy

Do you understand the meaning of "variable scope"?

If you don't, look it up. If you don't understand variable scope, you will never understand any explanation of why your code isn't working.

Okay, thanks. I thought I had already tried it before main (as global) just because I was trying it everywhere but now I understand why.

Originally Posted by grumpy

In your example, can you explain what the difference is between in i main() and i in either of the functions? Can you do the same for j (and other variables)?

The i in main is basically a counter.? (though there must be more to it than that since the recursion is going to be tied to it - I had the layout neat before switching the third column to recursion. Having the second two columns of iteration worked fine but the assignment requires each method).
The i in main is global and passed to the function.

The other variables just hold the numbers/integers for the calculations. I am thinking if I use the returned variable to main from the functions, then cout them, I could use local variables... and reuse the same variables. I also think that is what the teacher is intending us to do, otherwise there is no need to return the data (aside to end the function). But then if I declare them in the function and initilize them they will be reinitilized each time the function is called, like starting from the beginning right?

Code:

 /*
Author : Calvin
Description : displays first 21 numbers in the Fibonacci sequence
*/




// INCLUDES AND NAMESPACES
#include <iostream>
#include <iomanip>
using namespace std;


// GLOBAL VARIABLES
int i = 0;


int j = 0;
int k = 1;
int l = 1;


int m = 0;
int n = 1;
int o = 1;
 
// PROTOTYPES
int FibonacciIterative(int);
int FibonacciRecursive(int);
 
// MAIN
int main() {
    int i = 0;
    cout << "LETS LOOK AT THE FIBONACCI SEQUENCE...\n\n";
    cout << "ELEMENT\t\tITERATIVE\tRECURSIVE\n";
    for (int i = 0; i <= 20; i++) {
        cout << i << "\t\t";
        FibonacciIterative(i);
        FibonacciRecursive(i);
    }


    return 0;
}
 
// FUNCTION IMPLEMENTATIONS
// returns F_i of the Fibonacci sequence (iterative)
int FibonacciIterative(int i) {


    if (i == 0) {
        j = 0;
        k = 1;
        l = 1;
        cout << l-1 << "\t\t";
    }


    else {
    cout << l << "\t\t";
    l = j + k;
    j = k;
    k = l;
    
    }
    return l;
    
}
 
// returns F_i of the Fibonacci sequence (recursive)
int FibonacciRecursive(int i) {


    if (i == 0) {
        m = 0;
        n = 1;
        o = 1;
        cout << o-1 << '\n';
    }


    else if (i < 2) {
        cout << o << "\n";
        o = m + n;
        m = n;
        n = o;
    }


    else {
        o = FibonacciRecursive(i-1) + FibonacciRecursive(i-2);
        cout << o << "\n";
    }


    return o;
}

Originally Posted by grumpy

In the code in your opening post there are declarations of i,j,k, and l in main(). Within the function FibonacciIterative() there are also declarations of i (as a function parameter), as well as declarations of j,k, and l.

What is the relationship, if any, between i in main() and i in FibonacciIterative()? Also, what is the relationship, if any, between j in main() and j in FibonacciIterative()?

The i in main is passed to the function so there is a close/tied relationship. Therefore I declared it globally and can remove the main declaration. It is not declared in the functions.

There is no relationship between the j or k (from Fib iterative) or the m or n (from Fib recursive) and main or each other.

The other two variables from the functions (l and o) are returned to main but main is currently not dependant on them; unless I output the result in main rather than from the function.

Am I getting closer? I googled a little on it but mostly got info on the relationship between variables (causal, correlation, affine...). It seems to be a pretty direct relationship with i and none for the rest as they are not used in main.

(Since I need the variable retained for the further calls to the functions do I need them global so they don't get re-initilized? I can't declare them in the if statement but I did try so they would only be initilized the first time.)