Auto and Static Variable in C

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Introduction to Auto Variables in C

Auto variables are fundamental components of C programming, serving as temporary storage within function scopes.

They are declared without any storage specifier and are automatically initialized with garbage values if not explicitly assigned.

Auto variables have a local scope, limited to the function in which they are declared, and are suitable for managing short-lived data during program execution.

Characteristics of Auto Variables:

Local Scope: Confined to the scope of the function in which they are declared.

Automatic Storage Duration: Created upon function invocation and destroyed upon function exit.

Default Initialization: Not explicitly initialized, leading to the presence of garbage values until assigned.

Stack Allocation: Reside in the stack memory, facilitating efficient memory allocation and deallocation within function contexts.

Program Example for Auto Variables:

// Program for auto variable in C
#include <stdio.h>

void autoExample() {
    auto int num = 10;
    printf("Auto Variable: %d\n", num);
    num++;
}

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

Output:

Auto Variable: 10
Auto Variable: 10

Introduction to Static Variables in C

Static variables play a crucial role in retaining values across function calls in C programming.

Unlike auto variables, static variables persist their values between successive function invocations, offering long-term storage.

They are declared using the "static" keyword within a function scope or globally outside any function and have a lifetime equivalent to the entire program's execution.

Characteristics of Static Variables:

Persistent Value Retention: Preserve their values between function calls, offering persistent storage across invocations.

Lifetime Spanning Program Execution: Exist throughout the program's execution, maintaining values until program termination.

Single Initialization: Initialized only once, during program startup, ensuring consistent initial values across function calls.

Data Segment Allocation: Occupy memory in the data segment, enabling efficient access and management of long-term data.

Program Example for Static Variables:

// Program for static variable
#include <stdio.h>

void staticExample() {
    static int count = 0;
    printf("Static Variable: %d\n", count);
    count++;
}

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

Output: