Week 7 & 8 Syntax Guide

Nested Loops

A loop inside another loop. The inner loop completes all its iterations for every single iteration of the outer loop.

Syntax:

for (int i = 0; i < outerLimit; i++) {       // Outer Loop
    for (int j = 0; j < innerLimit; j++) {   // Inner Loop
        // Code to run
    }
}

Example:

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 2; j++) {
        printf("i=%d, j=%d\n", i, j);
    }
}

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 2; j++) {
        cout << "i=" << i << ", j=" << j << "\n";
    }
}

2D Arrays

A 2D array is essentially a matrix with rows and columns.

1. Declaration

Syntax:

DataType arrayName[rows][columns];

Example:

int matrix[3][4]; // 3 rows, 4 columns

2. Initialization

Method A: Nested Braces (Recommended)

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

Method B: Linear List

int matrix[2][3] = {1, 2, 3, 4, 5, 6}; // Fills row by row

Method C: Partial Initialization

int matrix[2][3] = {
    {1},    // Becomes {1, 0, 0}
    {4, 5}  // Becomes {4, 5, 0}
};

3. Accessing Elements

Syntax:

arrayName[rowIndex][colIndex] = value;

Example:

matrix[0][1] = 10;      // Assigns 10 to row 0, col 1
int x = matrix[1][2];   // Reads value from row 1, col 2

Processing 2D Arrays

We use nested loops to iterate through 2D arrays.

Common Pattern (Row-Major Order):

for (int i = 0; i < rows; i++) {           // Iterate Rows
    for (int j = 0; j < cols; j++) {       // Iterate Columns
        printf("%d ", matrix[i][j]);       // Process Element
    }
    printf("\n");
}

for (int i = 0; i < rows; i++) {           // Iterate Rows
    for (int j = 0; j < cols; j++) {       // Iterate Columns
        cout << matrix[i][j] << " ";      // Process Element
    }
    cout << "\n";
}

2D Arrays in Functions

1. Prototype

In C, pass rows and cols before the array:

ReturnType functionName(int rows, int cols, DataType arr[][cols]);

Example:

void printMatrix(int rows, int cols, int arr[][cols]);
int  sumMatrix(int rows, int cols, int arr[][cols]);

In C++, the column size must be a compile-time constant (#define):

#define COLS 4
ReturnType functionName(DataType arr[][COLS], int rows, int cols);

Example:

void printMatrix(int arr[][COLS], int rows, int cols);
int  sumMatrix(int arr[][COLS], int rows, int cols);

2. Calling the Function

int matrix[3][4];
printMatrix(3, 4, matrix);   // rows and cols first, then array name

int matrix[3][COLS];
printMatrix(matrix, 3, COLS);  // array first, then rows and cols

3. Processing Pattern Inside a Function

void processMatrix(int rows, int cols, int arr[][cols]) {
    for (int i = 0; i < rows; i++) {       // Iterate rows
        for (int j = 0; j < cols; j++) {   // Iterate columns
            // Use arr[i][j]
        }
    }
}

void processMatrix(int arr[][COLS], int rows, int cols) {
    for (int i = 0; i < rows; i++) {       // Iterate rows
        for (int j = 0; j < cols; j++) {   // Iterate columns
            // Use arr[i][j]
        }
    }
}