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1. Introduction
In C programming, variables can be classified as local or global based on their scope and lifetime. Local variables are declared inside a function or block and can only be used within that function or block. Global variables are declared outside all functions, usually at the top of a program file, and can be accessed from any function within the file.
2. Key Points
1. Local variables have a scope limited to the function or block in which they are declared.
2. Global variables are accessible from any part of the program after their declaration.
3. The lifetime of a local variable is limited to the execution of the function or block.
4. Global variables exist throughout the lifetime of the program.
3. Differences
| Local Variable | Global Variable |
|---|---|
| Declared within a function or block. | Declared outside of all functions, typically at the top of the file. |
| Scope is limited to the function or block where it is declared. | Accessible throughout the program from any function after its declaration. |
| Lifetime is limited to the execution of the function or block. | Lifetime is throughout the program's execution. |
4. Example
#include <stdio.h>
int globalVar = 10; // Global variable
void function() {
int localVar = 20; // Local variable
printf("Inside function, localVar: %d, globalVar: %d\n", localVar, globalVar);
}
int main() {
printf("In main, globalVar: %d\n", globalVar);
function();
// printf("In main, localVar: %d\n", localVar); // This would cause a compile-time error
return 0;
}
Output:
In main, globalVar: 10 Inside function, localVar: 20, globalVar: 10
Explanation:
1. globalVar is accessible both in the main function and inside function.
2. localVar is only accessible within function and trying to access it in main would result in a compile-time error.
5. When to use?
- Use local variables for temporary storage that is only relevant within a certain block or function.
- Use global variables for data that needs to be accessed by multiple functions throughout a program.
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