📦 Session 11: Arrays

Storing Many Values

Store 100 numbers in one variable? Yes, with arrays!

Marks of 50 students? A list of scores? One name, many boxes.

One array → Many values ✨

Today's Array Mission

📦

Declare an array
Type, name, size

🔢

Index (0-based)
First element is 0

🔄

Loops + arrays
Fill, print, sum

📥

Read & write
scanf/printf with arr[i]

📊

Simple programs
Sum, max, marks

🚨

Common traps
Bounds, off-by-one

🤔 Why Arrays? Without vs With

❌ Without array (5 marks)

int m1, m2, m3, m4, m5;
scanf("%d", &m1);
scanf("%d", &m2);
// ... 50 variables for 50 students? 😫
                        

Too many variables!

✅ With array

int marks[50];
for (i=0; i<50; i++)
    scanf("%d", &marks[i]);
                        

One name, 50 boxes. 🎉

Same type • One name • Use a loop

📦 Declaring an Array

Type, name, and size in square brackets. Size is fixed.

// Syntax: type name[size];
int marks[5];      // 5 integers
float scores[10];  // 10 floats
int arr[100];    // 100 integers
            

📌 Fixed size

You choose size when you write the program (e.g. 5, 10, 50).

📌 Same type

All elements are the same type (all int or all float).

🔢 Index: Start from 0!

First element is index 0, not 1. Last element is size - 1.

int arr[5];

[0]
10

[1]
20

[2]
30

[3]
40

[4]
50

Valid indices: 0, 1, 2, 3, 4. Never use 5 (out of bounds!).

📥 Reading & Writing Array Elements

// Write: arr[index] = value;
arr[0] = 10;
arr[1] = 20;

// Read: use arr[index] in expressions
printf("%d", arr[0]);   // print first
scanf("%d", &arr[2]); // read into third
            

Use & when reading into arr[i] with scanf: &arr[i]

🔄 Loop: Fill and Print Array

int arr[5], i;

// Fill from user
for (i = 0; i < 5; i++) {
    printf("Enter value %d: ", i + 1);
    scanf("%d", &arr[i]);
}

// Print all
for (i = 0; i < 5; i++) {
    printf("%d ", arr[i]);
}
            

Always use i < 5 (not i <= 5). Last index is 4.

➕ Sum of All Elements

int arr[5] = {10, 20, 30, 40, 50};
int sum = 0, i;

for (i = 0; i < 5; i++) {
    sum = sum + arr[i];
}
printf("Sum = %d\n", sum);  // 150
            

Initializer: int arr[5] = {10, 20, 30, 40, 50};

📊 Find the Maximum

int arr[5], i, max;

// assume first is max
max = arr[0];
for (i = 1; i < 5; i++) {
    if (arr[i] > max)
        max = arr[i];
}
printf("Max = %d\n", max);
            

Start from index 1; compare each with max.

📚 Marks of 50 Students (as in Session 10!)

int marks[50], i, sum = 0;

for (i = 0; i < 50; i++) {
    printf("Mark for student %d: ", i + 1);
    scanf("%d", &marks[i]);
    sum = sum + marks[i];
}
printf("Average = %f\n", sum / 50.0);
            

One array, one loop: store and add. Then average!

🚨 Array Traps

❌ Out of bounds

arr[5] when size is 5 — valid indices are 0 to 4 only!

❌ Wrong loop condition

i <= 5 for arr[5] — last index is 4. Use i < 5.

❌ Forgetting & in scanf

scanf("%d", arr[i]); — must be &arr[i] for integers.

❌ Index 1 to N

Use 0 to N-1. First element is arr[0], not arr[1].

🧠 Array Quiz!

In int arr[10], valid indices are 0 to 9.

First element of an array is at index 1.

We use a loop to fill or print many elements easily.

arr[10] for int arr[10] is valid (last element).

🏆 Array Mastery Unlocked!

You've earned these badges:

📦 Array Declarer

🔢 Index Master (0-based)

🔄 Loop + Array Pro

📊 Sum & Max

📚 50 Students Ready

You can store many values in one variable—like a pro! 🚀

🏠 Your Coding Mission!

📥 Read 5 numbers

Store in array, then print them

➕ Sum & average

Array of 10, find sum and average

📊 Max and min

Find largest and smallest in array

📚 Marks

Store marks of N students, print average

🚀 What's Coming Next!

Strings: Working with Text

Store names and sentences? Strings are arrays of characters!

🤔 Think About This Week:

How would you store a person's name in C?