Technical Stuff

Auto is the default storage class for the local varaibles. Auto is a short form for Automatic.

• Keyword : auto
• Default value : Garbage value
• Memory Location : Main memory
• Scope : Local to the block or function
• Lifetime : Till the application runs or until memory location destroys

Default value sample code:

int main()
{
 auto int a;
 int i;
 printf("a is %x\ni is %d\n",a,i);
}

OutPut:
a is 0
i is 0

In the above code, two integer variables are declared as automatic , in that one is using keyword and another one is without keyword. both variables behaviour is same. They are not inittialised, so default value is garbage value. Here in the output , it is zero. Defualt value is depends on the machine. I am using Unix, so got default value zero. If you use Windows , you may get garbage value. So if you not initialise the variable, result is undefined. So its always better to initialise the variables.

Variable initialization:

int main()
{
 auto int a=20;
 int i=20;
 printf("a is %x\ni is %d\n",a,i);
}

OutPut:
a is 20
i is 20

In the above code, two integer variables are declared as automatic , in that one is using keyword and another one is without keyword. both variables behaviour is same.

Scope or visibility sample code:

int main()
{
 auto int a=20;
 {
 int a = 30; // scope is limited to this block
 int i=20; // scope is limited to this block
 printf("a is %d\ni is %d\n",a,i);
 }
 // we cant access i here
 // a is first declared variable and not the second declared variable
 printf("a is %d\n",a); 
}

OutPut:
a is 30
i is 20
a is 20

In the above code, on integer varibale a is declared in a main block, another two variabels a and i declared in the separted block. second variable a and i are limited to this block only. If second variable is not declared in the block, first declared a variable scope comes to this block also.

Labels: C program, Programming in C, Storage Classes