FUNCTIONS

1️⃣ Without Parameter & Without Return Value
👉 No input
👉 No output

#include <stdio.h>

void greet(void)
{
    printf("Hello\n");
}

int main()
{
    greet();
    return 0;
}
✔ Used when function just performs an action (like LED ON).


2️⃣ With Parameter & Without Return Value
👉 Takes input
👉 Does not return anything

#include <stdio.h>

void printSquare(int num)
{
    printf("Square = %d\n", num * num);
}

int main()
{
    printSquare(5);
    return 0;
}
✔ Used when function performs operation but no need to send result back.

3️⃣ Without Parameter & With Return Value
👉 No input
👉 Returns output

#include <stdio.h>

int getNumber(void)
{
    return 10;
}

int main()
{
    int value = getNumber();
    printf("%d", value);
    return 0;
}
✔ Used when function generates or reads a value (like ADC read).

🔹 4️⃣ With Parameter & With Return Value ⭐ (Most Important)
👉 Takes input
👉 Returns output

C

#include <stdio.h>

int add(int a, int b)
{
    return a + b;
}

int main()
{
    int result = add(5, 3);
    printf("Sum = %d", result);
    return 0;
}
✔ Most commonly used in embedded systems.

🔥 Summary Table
Type	Parameter	Return	Usage
1	❌	❌	Simple action
2	✅	❌	Action using input
3	❌	✅	Generate value
4	✅	✅	Process and return result

🎯 Embedded Example Mapping
Embedded Task	Function Type
LED ON	        -        No param, No return
Set PWM duty	  -        With param, No return
Read ADC	      -        No param, With return
Calculate CRC	  -        With param, With return

🚀 Interview Style Answer
Functions in C are classified into four types based on the presence of parameters and return values: with/without parameters and with/without return value. The most commonly used type in embedded systems is with parameters and with return value.



🔹 “Return” and “Output” Are NOT the Same
There are two different things:

1️⃣ Returning a value → sends value back to the calling function
2️⃣ Printing output → displays something on the screen

These are completely different.