Lecture120 Global variables

Lecture120 Global variables - Quadratic Equation Program...

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Lecture 1 -- 1 Computer Science I - Martin Hardwick Quadratic Equation Program Remember the quadratic equation program that from several weeks ago. it takes the coefficients A, B, and C of a quadratic equation  Ax 2  +Bx +C = 0  and computes the real roots using the quadratic equation We want to convert this program into a function that can easily be used in any program that needs to compute the roots of a quadratic equation. the function computes and returns the roots given the  coefficients A, B, and C Problem: there may be zero, one, or two roots and a function can return at most one value using the return mechanism. B 2 – 4AC 2A x = -B ±
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Lecture 1 -- 2 Computer Science I - Martin Hardwick Returning Multiple Values From a Function There are two ways to return multiple values from a function: global variables reference parameters The preferred approach is to use reference parameters. Global Variables – special variables that are available for all functions to use. hence, one function can put a value into a global variable and  another function can retrieve that value from the global variable Reference Parameters – special type of parameter that lets a called function change the value of the corresponding argument variable in the calling function.
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Lecture 1 -- 3 Computer Science I - Martin Hardwick Global Variables #include <iostream> using namespace std; // global variables int a,b; void func1 () // called first { a = 10;   // global a b = 2; // global b . . . } void func2() // called last { int b,c; c = a; // global a cout << c; b = 1; // local b . . . } A global variable is a variable declared at the beginning of a program outside all functions. remember, variables  declared inside a function  are local to that function All functions can use a global. unless a function has a  local variable or parameter  with the same name as a  global variable in this case, the global  variable is hidden from the  function Global variables make programs hard to read and understand. therefore, don’t use them
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Lecture 1 -- 4 Computer Science I - Martin Hardwick Parameter Passing In Functions In all the programs we have seen so far, the arguments in a function call provide data needed by the called function they pass data into the function There are times when a function wants to use its parameters to pass
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Lecture120 Global variables - Quadratic Equation Program...

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