Activity: C Review & Functions

Brief Intro — C Review & Functions

Instead of writing one giant block of code, programmers break complex problems into smaller, reusable pieces called functions. C is built on this modular approach, allowing you to "call" a specific task whenever you need it.

In this activity, you will explore how to define your own functions and how data is passed between them using values and references.

C is a powerful system language that has shaped modern computing, from operating systems like UNIX to high-performance databases.

Task 1: Origins of C

Who developed C, and for what purpose?

Dennis M. Ritchie at Bell Labs, to develop the UNIX operating system Brian Kernighan at IBM, to develop Linux Bjarne Stroustrup at Microsoft, to develop Windows Ken Thompson at Apple, to develop DOS

Check Answer

Correct Answer: Dennis M. Ritchie at Bell Labs, to develop the UNIX operating system. C was first implemented on the DEC PDP-11 in 1972, and Kernighan and Ritchie (K&R) produced the first description in 1978.

Task 2: Facts about C

Select ALL the true statements about C.

C is a successor of the B language, introduced around the early 1970s C was formalized in 1988 by the American National Standards Institute (ANSI) The UNIX operating system was totally written in C C was developed by Microsoft in the 1990s C is the most widely used system programming language today

Check Answer

Correct Answer: a, b, c and e are true. C is a successor of B; it was formalized by ANSI in 1988; UNIX was totally written in C; and it is the most widely used system programming language. Linux and MySQL are also written in C.

Task 3: Why use C?

Which reason best explains why C became a widely used professional language?

It produces code that runs nearly as fast as assembly, and it is easy to learn, structured, efficient, and portable It can run on only one kind of computer platform It is the newest programming language with no history It cannot handle low-level activities

Check Answer

Correct Answer: a. C is easy to learn, structured, produces efficient programs, handles low-level activities, compiles on a variety of platforms, and runs nearly as fast as assembly.

Task 4: Uses of C

Match each example to the use-of-C category it belongs to.

UNIX and Linux

The C compiler itself

MySQL

Programs that control network hardware

Check Answer

Correct Answer: UNIX and Linux → Operating Systems; the C compiler → Language Compilers; MySQL → Databases; network hardware programs → Network Drivers. Other listed uses include Assemblers, Text Editors, Print Spoolers, Modern Programs, Language Interpreters, and Utilities.

Functions follow a precise structure: you declare their presence, define their behavior, and finally call them to perform a task.

Task 5: What is a function?

A function is a group of statements that together perform a task. Every C program has at least one function — main(). What best describes a function?

A group of statements that together perform a task A single variable declaration A hardware component of the computer A type of data file

Check Answer

Correct Answer: a. A function is a group of statements that together perform a task, and each function performs a specific task.

Task 6: Declaration vs Definition

The declaration tells the compiler about a function's name, return type, and parameters. The definition provides the actual body of the function. Which statement is correct?

Declaration states the name, return type and parameters; definition provides the body Definition states the name and return type; declaration provides the body Declaration and definition are exactly the same thing A declaration is only needed for library functions

Check Answer

Correct Answer: a. The C standard library also provides built-in functions like strcat() (concatenates two strings) and memcpy() (copies memory).

Task 7: Anatomy of max()

Trace this code: int a = 100; int b = 200; int ret; ret = max(a, b); printf("Max value is : %d", ret); What is printed?

int max(int num1, int num2) {
    int result;
    if (num1 > num2)
        result = num1;
    else
        result = num2;
    return result;
}

Max value is : 200 Max value is : 100 Max value is : 0 Max value is : 20000

Check Answer

Correct Answer: a. The call ret = max(a, b); passes 100 and 200; max() returns the larger value, 200, which is stored in ret and printed as Max value is : 200.

Task 8: Control Flow

When a program calls a function, what happens to program control?

Control transfers to the called function, and returns when its return statement executes or its closing brace is reached Control stays in main() and the function runs at the same time Control jumps to the start of the program Control terminates the program

Check Answer

Correct Answer: a. The called function performs its task, then returns control to the main program via return or its closing brace.

Deciding whether to pass data by value or by reference determines whether a function can modify the original variables in your main program.

Interactive Simulator: Call by Value vs Call by Reference Swapper

Step through the swap program. Watch what happens to m and n — and what happens only inside swap().

main()

void swap(int a, int b)

Call by value

Copies the actual values: a = 22, b = 44. The swap happens on the copies.

Inside swap(): m = 44 and n = 22 (the labels point to a, b).

Back in main(): m = 22 and n = 44 — originals UNCHANGED.

Call by reference (the idea)

Passes the addresses of m and n, so the function works on the originals.

Result: the caller's m and n DO change.

By default, C uses call by value.

The full call-by-reference syntax (& and *) needs pointers, which the notes defer to the Pointers activity — we show only the idea here.

Task 9: Formal vs Actual Parameters

The variables declared in the function definition are the formal parameters; the arguments used in the function call are the actual parameters. Which is correct?

Formal parameters are declared in the function definition; actual parameters are used in the call Formal parameters are used in the call; actual parameters are declared in the definition Formal and actual parameters are always the same variable Only actual parameters exist in C

Check Answer

Correct Answer: a. Formal parameters behave like local variables: they are created on entry into the function and destroyed on exit.

Task 10: Call by Value

In call by value, changes made to a parameter inside the function have what effect on the actual argument?

No effect — the argument is unchanged They change the actual argument They delete the actual argument They crash the program

Check Answer

Correct Answer: a. Call by value copies the actual value into the formal parameter, so changes inside the function have no effect on the argument.

Task 11: Call by Reference

In call by reference, changes made to the parameter do what?

Affect the actual argument, because the address is used to access it Have no effect on the actual argument Affect only the copies inside the function Are ignored by the compiler

Check Answer

Correct Answer: a. Call by reference copies the address of the argument into the formal parameter; inside the function the address accesses the actual argument, so changes affect it. The notes defer the full syntax until after pointers are understood.

Task 12: Swap by Value — Trace

After swap(m, n) is called by value with m = 22, n = 44, what are the values of m and n in main()?

void swap(int a, int b) {
    int tmp;
    tmp = a;
    a = b;
    b = tmp;
}

m = 22 and n = 44 (unchanged) m = 44 and n = 22 m = 0 and n = 0 Undefined

Check Answer

Correct Answer: a. The swap happens on the copies a, b, so the originals stay 22 and 44. The program prints Values before swap m = 22 and n = 44; the copies print Values after swap m = 44 and n = 22.