Exercise 3-9 (static vs local variable inside a function)

Chapter_3     Exercise_3-8     Global

Exercise_3-10

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Exercise 3-9     TCP1, p. 228

Exercise 3-9. Compile and run Static.cpp. Remove the static keyword from the code, compile and run it again, and explain what happens.

CONTENTS:     Static.cpp     Local.cpp

Static.cpp     TCP1, p. 162         download

// Using a static variable in a function
#include <iostream>
using std::cout;
using std::endl;

void func();

int main()
{
for(int x = 0; x < 10; x++)
{func();}

return 0;
}

void func()
{
static int i = 0; // initialize at first function call
cout << "i = " << ++i << endl;
}
/*
g++ Static.cpp -o Static
./Static
i = 1
i = 2
i = 3
i = 4
i = 5
i = 6
i = 7
i = 8
i = 9
i = 10
*/

Note:  In Static.cpp, the static variable i is initialized the first time the function func() is called, then it preserves its value between function calls. After each function call, the value is incremented, so i varies between 1 and 10 (after ++i).

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Local.cpp         download

// Using a local variable in a function
#include <iostream>
using std::cout;
using std::endl;

void func();

int main()
{
for(int x = 0; x < 10; x++)
{func();}

return 0;
}

void func()
{
int i = 0; // initialize at every function call
cout << "i = " << ++i << endl;
}
/*
g++ Local.cpp -o Local
./Local
i = 1
i = 1
i = 1
i = 1
i = 1
i = 1
i = 1
i = 1
i = 1
i = 1
*/

Note:  Compared to Static.cpp, Local.cpp uses a local variable inside the function func(). Its value is not preserved between function calls. At the beginning of each function call, i is initialized to 0, its value is incremented and printed. The result is printing i = 1 ten times.

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