Variables in C -1
Example
// Here we are writing down the C programming language code to demonstrate
// the concept of Understanding the "extern" keyword in C with its relevant code
// and output supported by valid syntax where ever it's necessary
#include <stdio.h>
// the main driver code functionality starts from here
int main()
{
// declaration and definition of variable 'a123.'
// As we can see, there are character data type variables and definitions
// declared below as a_123
char a_123 = 'b';
// The variable 'b' is declared, and the memory has been allocated
// until an explicit usage is mad,e it is initialized with some garbage
// value
float a;
// As we can see, there are integer data type variables and definitions
// declared below as c, e, and _d45, respectively
int _c, _d45, e;
// The below code helps us in printing down the variables declared
printf("%c \n", a_123);
return 0;
// the main driver code functionality ends from here
}
Output:
Variables in C -2
Example
// Here we are writing down the C programming language code to demonstrate
// the concept of Understanding the "extern" keyword in C with its relevant
// code
// and output supported by valid syntax where ever it's necessary
#include <stdio.h>
void function(){
//here integer x is a local variable
int x = 120;
//here, integer y is a static variable
static int y = 130;
// below, we are performing operations over integer and static variables
x = x + 101;
y = y + 101;
// here, we are trying to print the variables after the operation
printf("\n%d,%d",x,y);
}
// The main driver code functionality starts from here
int main() {
// calling the function multiple times to verify the results
function();
function();
function();
return 0;
// The main driver code functionality ends from here
}
Output:
Output
221,231
221,332
221,433
Variables in C -3
Example
// Here we are writing down the C programming language code to demonstrate
// the concept of Understanding the "extern" keyword in C with its relevant
// code
// and output supported by valid syntax where ever it's necessary
#include <stdio.h>
void function()
{
int x=10;//local variable (also automatic)
auto int y=20;//automatic variable
}
// the main driver code functionality starts from here
int main() {
function();
return 0;
// the main driver code functionality ends from here
}
Output:
Output
Compiles without any error
Extern keyword
Example
// here we have written the c code of extern keyword declaration
#include <stdio.h>
extern int a;
// the main driver code functionality starts from here
int main()
{
printf("%d", a);
return 0;
// the main driver code functionality ends from here
}
Output:
Output
/usr/bin/ld: cannot open output file a.out: Permission denied
collect2: error: ld returned one exit status
The following code compiles without any errors and executes successfully.
Example
// here, we have written multiple cases where the C compiler runs
// successfully without throwing any error (example-1)
extern int var;
// the main driver code functionality starts from here
int main(void)
{
// no var variable declared it is declared outside the main driver code
return 0;
}
// example-2
extern int var;
// the main driver code functionality starts from here
int main(void)
{
// the var variable here holds the value of 10
var = 10;
return 0;
}
// example-3
#include "somefile.h"
extern int var;
// the main driver code functionality starts from here
int main(void)
{
// the var variable here holds the value of 20
var = 20;
return 0;
}
// example-4
extern int var = 0;
// the main driver code functionality starts from here
int main(void)
{
// the var variable here holds the value of 100
var = 100;
return 0;
}