Arrays

An array stores multiple values of the same type in contiguous memory.

#include <stdio.h>

int main() {
    // Declare and initialize
    int numbers[5] = {10, 20, 30, 40, 50};

    // Access elements (0-indexed!)
    printf("First: %d\n", numbers[0]);   // 10
    printf("Last: %d\n", numbers[4]);    // 50

    // Modify an element
    numbers[2] = 99;

    // Loop through array
    for (int i = 0; i < 5; i++) {
        printf("%d ", numbers[i]);
    }
    // Output: 10 20 99 40 50

    return 0;
}

2D Arrays (Matrices)

int matrix[3][3] = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

printf("%d\n", matrix[1][2]);  // 6 (row 1, col 2)

// Print entire matrix
for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
        printf("%d ", matrix[i][j]);
    }
    printf("\n");
}

Strings in C

In C, strings are arrays of characters ending with a null terminator '\0'.

#include <stdio.h>
#include <string.h>  // String functions

int main() {
    char name[50] = "Hello";

    // String functions
    printf("Length: %lu\n", strlen(name));     // 5
    
    char copy[50];
    strcpy(copy, name);       // Copy string
    
    strcat(name, " World");   // Concatenate
    printf("%s\n", name);     // Hello World
    
    // Compare strings
    if (strcmp(name, "Hello World") == 0) {
        printf("Strings are equal!\n");
    }
    
    return 0;
}

Common String Functions

✅ Quick Quiz

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