Scope of variables - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of variable shadowing in nested blocks

What is the output of this C code?

C

#include <stdio.h>

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

A 10\n10\n

B 10\n5\n

C 5\n10\n

D 5\n5\n

💡 Hint

Remember that inner blocks can have variables with the same name that hide outer ones.

The inner block declares a new variable x with value 10, which shadows the outer x. So inside the block, x is 10. Outside, it remains 5.

❓ Predict Output

intermediate

Output of static variable inside function

What will be printed when this program runs?

C

#include <stdio.h>

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

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

A 0 0 0

B 0 1 2

C 1 2 3

D 1 1 1

💡 Hint

Static variables inside functions keep their value between calls.

The static variable count is initialized once to 0, then incremented each call. So outputs are 1, then 2, then 3.

❓ Predict Output

advanced

Output of global and local variable with same name

What is the output of this program?

C

#include <stdio.h>

int val = 100;

void printVal() {
    int val = 50;
    printf("%d ", val);
}

int main() {
    printVal();
    printf("%d\n", val);
    return 0;
}

A 50 100\n

B 100 50\n

C 50 50\n

D 100 100\n

💡 Hint

Local variables hide global variables inside their scope.

The function printVal has a local val set to 50, so it prints 50. The global val remains 100, printed in main.

❓ Predict Output

advanced

Output of uninitialized local variable

What will this program print?

C

#include <stdio.h>

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

A Undefined value (garbage) printed

B 0

C Compilation error due to uninitialized variable

D Runtime error

💡 Hint

Local variables are not automatically set to zero.

The local variable x is uninitialized and contains garbage data. Printing it shows an unpredictable value.

❓ Predict Output

expert

Output of variable scope with extern and static

Given these two files, what is the output when compiled and run together?

file1.c

#include 

static int count = 5;

void printCount() {
    printf("%d\n", count);
}

file2.c

#include 

extern int count;

int main() {
    printCount();
    printf("%d\n", count);
    return 0;
}

A 0\n0\n

B 5\n5\n

C Linker error\n

D 5\nLinker error\n

💡 Hint

Static variables have internal linkage and are not visible outside their file.

The count variable in file1.c is static, so it cannot be linked from file2.c. The call to printCount() works and prints 5, but the extern int count; in file2.c causes a linker error because count is not found.