Parameter Passing Techniques

Introduction

Arguments are copied by default. Pass addresses when the callee must mutate data owned by the caller.

Understanding the topic

Pass by value Copy of value — original unchanged.

Pass by pointer Address passed — callee can modify original.

• Pass by value — Copy of value — original unchanged.
• Pass by pointer — Address passed — callee can modify original.

Step-by-step explanation

1. Pass by value — Copy of value — original unchanged.
2. Pass by pointer — Address passed — callee can modify original.

Informative example

Example program:

#include <stdio.h>

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

int main(void) {
    int x = 1, y = 2;
    swap(&x, &y);
    printf("%d %d\n", x, y);
    return 0;
}

2 1

Execution workflow

Best practices

• Enable warnings: gcc -Wall -Wextra -std=c11 source.c -o app
• Give every variable a defined value before it is read.
• Stay inside array bounds — C will not stop you from over-running a buffer.

Common mistakes

• Reading uninitialized storage — behavior is undefined.
• Dismissing compiler warnings instead of fixing root causes.
• Ignoring NULL returns from malloc, fopen, and similar APIs.

Hands-on exercise

Practice problems:

• Swap two numbers with pointers
• Modify array element in function

Summary

Parameter Passing Techniques in C — By-value copies versus by-address updates.