Variable scope and lifespan in C

C Fundamentals

Expressions & Operators In C

Data Input Output In C

Control Statements In C

Arrays & Strings In C

Functions In C

Pointers In C

Structure, Union & Enumeration In C

File Handling In C

C Preprocessor

Variable scope and lifespan

Scope -

• Refers to where in a program a particular variable is known
• Global variables are known in all parts of the source module following their declaration
• Local variables are known only within the block (usually a function) in which they are declaration
• Local variables are known only within the block (usually a function) in which they are declared
• A local variable can have same name as a global variable or local variable declared in a higher – level block, in which case the most local copy is used

Lifespan -

Global variables -

• Defined outside any function, usually before first function definition
• Known to all functions after the variable is defined
• Memory space is allocated at compile time
• If not explicitly initialized, a global variable is set to zeros
• Use only when absolutely necessary
• Do not use global variables just to avoid learning how to properly pass arguments (using structures, pointers, etc.)
•  In the following example, both main and largest refer to the same variables x and y

#include<stdio.h>
int x = 15, y = 20;         /* global variables */
void main ()
{
   int sum;         /*sum is local to main () */
   sum = x+y;
    . . . .
}
void largest (. . .)
{
    int max;
    max;
   . . . .
}

Local variables -

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