Section 6.6.2 Arrays and Pointers: Passing Single-Dimensional Arrays to Functions

Section 6.6.2 Arrays and Pointers: Passing Single-Dimensional Arrays to Functions#

Adapted from: “Beej’s Guide to C Programming” by Brian (Beej Jorgensen) Hall: Beej’s Guide to C Programming: 6.6.2 Arrays and Pointers: Passing Single Dimensional Arrays to Functions

Brian (Beej Jorgensen) Hall Website

Program for Demonstrating Passing Single-Dimensional Arrays to Functions#

#include <stdio.h>

// Passing as a pointer to the first element
void times2(int *a, int len)
{
    for (int i = 0; i < len; i++)
        printf("%d\n", a[i] * 2);
}

// Same thing, but using array notation
void times3(int a[], int len)
{
    for (int i = 0; i < len; i++)
        printf("%d\n", a[i] * 3);
}

// Same thing, but using array notation with size
void times4(int a[5], int len)
{
    for (int i = 0; i < len; i++)
        printf("%d\n", a[i] * 4);
}

int main(void)
{
    int x[5] = {11, 22, 33, 44, 55};

    times2(x, 5);
    times3(x, 5);
    times4(x, 5);
}

Explanation of the Above Code#

This C program demonstrates how to pass single-dimensional arrays to functions in different ways and perform operations on their elements. Here’s a breakdown of the code:

Code Explanation:#

1. #include <stdio.h>#

  • Includes the standard input/output library to use functions like printf.

2. Function: times2#

void times2(int *a, int len)
{
    for (int i = 0; i < len; i++)
        printf("%d\n", a[i] * 2);
}

  • This function takes a pointer to the first element of an array (int *a) and its length (int len).

  • It iterates through the array using the pointer and multiplies each element by 2, printing the result.

3. Function: times3#

void times3(int a[], int len)
{
    for (int i = 0; i < len; i++)
        printf("%d\n", a[i] * 3);
}

  • This function uses array notation (int a[]) to accept the array and its length.

  • It performs the same operation as times2, but multiplies each element by 3.

4. Function: times4#

void times4(int a[5], int len)
{
    for (int i = 0; i < len; i++)
        printf("%d\n", a[i] * 4);
}

  • This function specifies the array size in its parameter (int a[5]), but this size is not enforced by the compiler.

  • It multiplies each element by 4 and prints the result.

5. main Function#

int main(void)
{
    int x[5] = {11, 22, 33, 44, 55};

    times2(x, 5);
    times3(x, 5);
    times4(x, 5);
}

  • Declares an integer array x with 5 elements: {11, 22, 33, 44, 55}.

  • Calls the three functions (times2, times3, times4) with the array x and its length (5).

Key Concepts:#

  1. Passing Arrays to Functions:

    • Arrays are passed to functions as pointers to their first element. For example, x in times2(x, 5) is equivalent to &x[0].

  2. Array Notation vs Pointer Notation:

    • int *a and int a[] are functionally equivalent when used as parameters. Both represent a pointer to the first element of the array.

  3. Output:

    • The program prints the elements of the array multiplied by 2, 3, and 4, respectively:

      22
44
66
88
110
33
66
99
132
165
44
88
132
176
220

Compile and Run Code#

Use Python to Change to Working Directory#

import os
root_dir = os.getcwd()

code_dir = root_dir + "/" + "C_Code"

os.chdir(code_dir)

build_command = os.system("gcc -o section_6_6_2_passing_single_dimensional_arrays_to_functions section_6_6_2_passing_single_dimensional_arrays_to_functions.c")

exec_status = os.system("./section_6_6_2_passing_single_dimensional_arrays_to_functions")

22
44
66
88
110
33
66
99
132
165
44
88
132
176
220