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Arrays and functions in C go hand in hand. When you pass an array to a function, you're actually passing a pointer to its first element. This allows functions to efficiently manipulate large datasets without copying entire arrays.

Understanding how arrays interact with functions is crucial. You can modify array elements within functions, affecting the original array. This powerful feature enables you to create flexible and efficient code for array manipulation and processing.

Passing arrays to functions

Array as function arguments

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  • Specify the array name without brackets in the function parameter list to pass an array as an argument
  • The function receives a pointer to the first element of the array when an array is passed as an argument
  • Pass the size of the array as a separate parameter since it is not automatically passed to the function
    • Enables the function to determine the number of elements in the array
    • Prevents accessing elements outside the valid range, avoiding undefined behavior
  • Functions can accept multidimensional arrays as arguments by specifying additional brackets in the parameter declaration
    • Example:
      void processMatrix(int matrix[][COLS], int rows)

Arrays passed by reference

Passing arrays by reference

  • Arrays are passed by reference to functions, meaning the function receives the memory address of the array instead of a copy of its elements
  • Modifications made to the array within the function affect the original array in the calling function
    • Enables efficient manipulation of array elements without the need for copying data
    • Avoids the overhead of copying large amounts of data, especially for large arrays
  • Passing arrays by reference is more efficient than passing them by value
    • Copying large arrays can be time-consuming and memory-intensive
    • Passing by reference allows direct access to the original array, reducing memory usage and improving performance

Implications of passing arrays by reference

  • Changes made to array elements within the function are reflected in the original array
    • Enables modification of array elements from within the function
    • Requires careful consideration to avoid unintended modifications
  • The function receives a pointer to the first element of the array
    • Allows the function to access and manipulate individual elements using array indexing notation
    • Provides flexibility in traversing and modifying the array elements

Modifying array elements

Accessing and modifying array elements within functions

  • Use the array indexing notation to access and modify individual elements of the array passed as an argument
    • Example:
      array[index] = value;
  • Utilize the pointer received as the parameter to access array elements
    • The pointer points to the first element of the array
    • Increment the pointer or use array indexing to access subsequent elements
  • Ensure that the function does not access array elements outside the valid range
    • Accessing elements beyond the array bounds leads to undefined behavior
    • Use the array size passed as a separate parameter to determine the valid range

Reflecting changes in the original array

  • Modifications made to array elements within the function are visible in the original array
    • The function directly modifies the memory locations of the array elements
    • Changes persist after the function returns
  • The calling function can access the modified array elements after the function call
    • Enables data exchange between the calling function and the called function
    • Allows for efficient manipulation and processing of array data

Returning arrays from functions

Returning pointers to arrays

  • In C, arrays cannot be directly returned from functions, but pointers to arrays can be returned
  • Return a pointer to the first element of the array from the function
    • Example:
      int* getArray() { static int arr[] = {1, 2, 3}; return arr; }
  • The calling function receives the pointer returned by the function
    • Can use the pointer to access the elements of the array
    • Example:
      int* ptr = getArray(); int value = ptr[0];

Memory allocation for returned arrays

  • Ensure that the memory allocated for the array remains valid after the function returns
  • Return a pointer to a statically allocated array
    • Static arrays have a fixed size and persist throughout the program execution
    • Suitable for returning fixed-size arrays
  • Dynamically allocate memory for the array using
    malloc()
    or
    calloc()
    • Allocates memory on the heap, which remains valid after the function returns
    • The calling function is responsible for freeing the allocated memory when it is no longer needed
    • Example:
      int* getArray() { int* arr = malloc(sizeof(int) * size); /* ... */ return arr; }
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© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Glossary
Glossary