Multiple declarations are the same for variables inside and outside the loop

Question

#include <stdio.h> int main() { int i; for ( i=0; i<5; i++ ) { int i = 10; printf ( "%d", i ); i++; } return 0; } 

In this variable, i declared outside the for loop, and it is again declared and initialized inside the for loop. How does C allow multiple declarations?

Answer 1

i outside the loop and i inside the loop are two different variables .

• External i will work throughout main .

• Inner i will only work for one iteration of the loop.

The inner shadow is external in this area:

 { int i = 10; printf ( "%d", i ); i++; } 

Due to shadow copy rules, it is not possible to refer to an external one while inside the aforementioned area.

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Note that it is not possible to declare two variables with the same name in the same scope :

 { int i = 0; int i = 1; // compile-time error } 

Answer 2

Variables in one area can mask variables in a higher area.

In this example, i defined inside the loop masks i defined outside. In the body of the loop, printf prints the value of internal i , which is 10. Then i++ runs again on internal i , setting it to 11.

When the loop goes to the bottom and comes back, the inner i goes beyond. Then the second and third for clauses act on the outer i . When the body of the loop is reintroduced, a new instance of internal i is defined and initialized to 10.

Answer 3

You should check the following page for definitions of the different types of areas that C variables can have.

http://aelinik.free.fr/c/ch14.htm

Your first int i is in the scope of the whole block, and the second int i has scope within this nested loop. After the external nested loop, source code version i is applied again.