Tutorial 7.2: Variable Scope

Variable Scope
All examples that have been presented in the previous tutorials declared variables in the block of function main(). These variables are known only within the block of function main() which means, the variables are not accessible outside of the block. This is also applied to variables which are defined within a block that is inside other block. But variables which are defined in the outer block are accessible in the inner block. This is illustrated in the following example.

#include <stdio.h>

int main()
{
 int a = 0;
 printf("a\tb\n");
 
 while(++a < 10) {
  int b = 1;
  printf("%d\t%d\n", a, b);
  ++b;
 }
 
 return 0;
}

In the example there are two variables declared,. Variable a is declared within function main() block and variable b is declared within while loop block. a is the outer block variable therefore it is accessible within inner block. But b is not accessible in the outer block because it is while loop variable. Thus if you try to print the value of b outside the while loop block, you will get an error message when you compile the program.

Variables declared outside any function is called global variables. A global variable is a variable that can be accessed in any function. Global variables are declared in the normal way except that (normally) they are declared before function main(). For example, variable c is a global variable since it is declared outside (before) function main().

#include <stdio.h>

int c = 10; // global variable

int main()
{
 ...
 
 return 0;
}

Next: Defining a Function