Unit 5: Return Statement and Arrays

Return Statement

The return statement is used inside a function to end its execution and (optionally) send a value back to the caller.

Two Main Uses:

1. Returning a value:

   In a function with a non-`void` return type (like int or float), return sends a value back.

   int add(int a, int b) { return a + b; // Returns the calculated sum } 

2. Terminating a `void` function:

   In a void function (which returns nothing), return; can be used to exit the function early.

   void printNumber(int n) { if (n < 0) { printf("Number is negative.\n"); return; // Exits the function here } printf("Number is: %d\n", n); } 

Arrays

An array is a collection of data items of the same data type, stored in contiguous (one after another) memory locations. This allows you to store a list of values (like 100 student scores) under a single variable name.

One-Dimensional Arrays

A 1D array is a simple list of elements.

Declaration:
data_type array_name[size];
Example: int scores[5]; (This reserves space for 5 integers).

Initialization:
int scores[5] = { 98, 87, 92, 79, 100 };

Accessing Elements (0-based Indexing):
Array elements are accessed using an index in square brackets []. The index always starts at 0.

• scores[0] is 98
• scores[1] is 87
• ...
• scores[4] is 100

Arrays are most powerfully used with for loops to iterate over the elements.

for (int i = 0; i < 5; i++) { printf("Element %d is %d\n", i, scores[i]); } 

Multi-Dimensional Arrays (2D Arrays/Matrices)

A multi-dimensional array is an "array of arrays." The most common is a 2D array, which is perfect for representing a matrix or a grid.

Declaration:
data_type array_name[rows][columns];
Example: int matrix[2][3]; (A matrix with 2 rows and 3 columns).

Initialization:
int matrix[2][3] = { { 1, 2, 3 }, // Row 0 { 4, 5, 6 } // Row 1 };

Accessing Elements (row, col):
You need two indices: matrix[row][col].

• matrix[0][0] is 1
• matrix[0][2] is 3
• matrix[1][1] is 5

2D arrays are traversed using nested for loops (one for rows, one for columns).

// Loop through each row for (int i = 0; i < 2; i++) { // Loop through each column in that row for (int j = 0; j < 3; j++) { printf("Element (%d, %d) is %d\n", i, j, matrix[i][j]); } } 

Code Examples (from Practicals)

Practical #8: Sorting an Array (Bubble Sort)

#include <stdio.h> #define SIZE 5 int main() { int arr[SIZE] = { 5, 1, 4, 2, 8 }; int i, j, temp; printf("Original array: "); for (i = 0; i < SIZE; i++) printf("%d ", arr[i]); printf("\n"); // Bubble Sort Algorithm for (i = 0; i < SIZE - 1; i++) { for (j = 0; j < SIZE - i - 1; j++) { if (arr[j] > arr[j + 1]) { // For ascending order // Swap elements temp = arr[j]; arr[j] = arr[j + 1]; arr[j + 1] = temp; } } } printf("Sorted array: "); for (i = 0; i < SIZE; i++) printf("%d ", arr[i]); printf("\n"); return 0; } 

Practical #9: Matrix Addition (2D)

#include <stdio.h> #define ROWS 2 #define COLS 3 int main() { int A[ROWS][COLS] = { {1, 2, 3}, {4, 5, 6} }; int B[ROWS][COLS] = { {9, 8, 7}, {6, 5, 4} }; int C[ROWS][COLS]; // Result matrix int i, j; // Add corresponding elements for (i = 0; i < ROWS; i++) { for (j = 0; j < COLS; j++) { C[i][j] = A[i][j] + B[i][j]; } } // Print the result matrix C printf("Resulting Matrix C (A+B):\n"); for (i = 0; i < ROWS; i++) { for (j = 0; j < COLS; j++) { printf("%d\t", C[i][j]); } printf("\n"); // Newline after each row } return 0; } 

Practical #10b: Determinant of a 3x3 Matrix (2D)

#include <stdio.h> int main() { int A[3][3]; long det; int i, j; printf("Enter the 9 elements of the 3x3 matrix:\n"); for (i = 0; i < 3; i++) { for (j = 0; j < 3; j++) { printf("Enter element A[%d][%d]: ", i, j); scanf("%d", &A[i][j]); } } // Calculate determinant by expanding along Row 0 // det = a(ei - fh) - b(di - fg) + c(dh - eg) det = A[0][0] * (A[1][1] * A[2][2] - A[1][2] * A[2][1]) - A[0][1] * (A[1][0] * A[2][2] - A[1][2] * A[2][0]) + A[0][2] * (A[1][0] * A[2][1] - A[1][1] * A[2][0]); printf("The determinant of the matrix is: %ld\n", det); return 0; } 

Unit 5: Exam Quick Tips