Lifetime and scope comparison - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of variable with block scope

What is the output of this C program?

C

#include <stdio.h>

int main() {
    int x = 5;
    {
        int x = 10;
        printf("%d ", x);
    }
    printf("%d\n", x);
    return 0;
}

A 10 10

B 5 10

C 10 5

D 5 5

💡 Hint

Remember that variables declared inside a block have their own scope.

The inner block declares a new variable x that shadows the outer x. Inside the block, x is 10. Outside, it is 5.

❓ Predict Output

intermediate

Output of static variable in function

What is the output of this C program?

C

#include <stdio.h>

void counter() {
    static int count = 0;
    count++;
    printf("%d ", count);
}

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

A 1 2 3

B 0 1 2

C 1 1 1

D 3 3 3

💡 Hint

Static variables keep their value between function calls.

The static variable count is initialized once and keeps incrementing each call, so outputs 1, 2, 3.

🔧 Debug

advanced

Identify the error with variable lifetime

What error will this C code produce when compiled or run?

C

#include <stdio.h>

int* getPointer() {
    int x = 10;
    return &x;
}

int main() {
    int* p = getPointer();
    printf("%d\n", *p);
    return 0;
}

A Runtime error: segmentation fault or undefined behavior

B Compilation error: returning address of local variable

C Output: 10

D Compilation warning but runs and prints 0

💡 Hint

Think about the lifetime of local variables after the function returns.

The function returns address of a local variable which is destroyed after return. Using it causes undefined behavior, often a runtime crash.

🧠 Conceptual

advanced

Which variable has static lifetime?

Given these variable declarations, which one has static lifetime and global scope?

C

int global_var;

void func() {
    static int static_var = 0;
    int local_var = 0;
}

A All have static lifetime

B global_var

C local_var

D static_var

💡 Hint

Global variables exist for the whole program run.

Global variables have static lifetime. Static local variables also have static lifetime but limited scope. Local variables have automatic lifetime.

❓ Predict Output

expert

Output of nested static and automatic variables

What is the output of this C program?

C

#include <stdio.h>

void f() {
    static int s = 0;
    int a = 0;
    s++;
    a++;
    printf("%d %d\n", s, a);
}

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

A

0 1
1 1
2 1

B

1 1
1 1
1 1

C

1 0
2 0
3 0

D

1 1
2 1
3 1

💡 Hint

Static variables keep their value between calls; automatic variables reset each call.

Static variable s increments and keeps value across calls. Automatic variable a resets to 0 each call then increments to 1.