📘 Introduction to C Language Arrays: Storing Multiple Data at Once!

Author: IoT Smart Academy

🧠 1. Why Do We Need Arrays?

In previous programs, we could only use single variables:

int a, b, c, d, e;

What if we need to store the scores of 100 students? Should we write 100 variables?😰

✅ Solution: Array allows us to store a group of data of the same type under one name.

✨ 2. Definition and Initialization of Arrays

data_type array_name[element_count];

For example:

int score[5];    // Define 5 integers
float temp[10];  // Define 10 floats
char name[20];   // Define a string array

📌 Memory Representation:

Index	Element	Description
0	score[0]	First element
1	score[1]	Second element
…	…	…
4	score[4]	Fifth element

✅ Initialization Methods

int a[5] = {1, 2, 3, 4, 5};
float b[] = {3.5, 4.2, 1.8};

✅ If the length is omitted, the system automatically calculates the number of elements.

🌟 3. Array Input and Output (Using for Loop)

Arrays are often used in conjunction with loops:

#include <stdio.h>
int main() {
    int score[5];
    int i;

    printf("Please enter the scores of 5 students:\n");
    for (i = 0; i < 5; i++) {
        scanf("%d", &score[i]);
    }

    printf("The entered scores are:\n");
    for (i = 0; i < 5; i++) {
        printf("%d ", score[i]);
    }
    printf("\n");
    return 0;
}

✅ Output Result:

Please enter the scores of 5 students:
80 90 75 85 95
The entered scores are:
80 90 75 85 95

📍 Key Points:

Index starts from 0
Use &score[i] for input, and score[i] for output

🧮 4. Example 1: Calculate Average Score and Highest Score

#include <stdio.h>
int main() {
    int score[5];
    int i, max = 0;
    float sum = 0;

    printf("Please enter 5 scores:");
    for (i = 0; i < 5; i++) {
        scanf("%d", &score[i]);
        sum += score[i];
        if (score[i] > max) max = score[i];
    }

    printf("Average score: %.2f\n", sum / 5);
    printf("Highest score: %d\n", max);

    return 0;
}

📌 Knowledge Points:

sum accumulates the total
max updates the maximum value
Note type conversion: sum/5 → decimal output

📊 5. Example 2: Count Pass and Fail Students

#include <stdio.h>
int main() {
    int score[10];
    int i, pass = 0, fail = 0;

    printf("Please enter 10 scores:");
    for (i = 0; i < 10; i++) {
        scanf("%d", &score[i]);
        if (score[i] >= 60)
            pass++;
        else
            fail++;
    }

    printf("Number of pass: %d\n", pass);
    printf("Number of fail: %d\n", fail);

    return 0;
}

✅ Thought Process:

Use two counters to count the numbers
Utilize if for conditional branching
Commonly used in IoT sensor data statistics (e.g., temperature limit detection)

🔢 6. Example 3: Reverse Output of Array Elements

📌 Scenario: Display historical records of sensor sampling (view in reverse)

#include <stdio.h>
int main() {
    int data[5];
    int i;

    printf("Please enter 5 numbers:");
    for (i = 0; i < 5; i++) {
        scanf("%d", &data[i]);
    }

    printf("Reverse output result:\n");
    for (i = 4; i >= 0; i--) {
        printf("%d ", data[i]);
    }
    printf("\n");

    return 0;
}

✅ Output Example:

Input: 10 20 30 40 50
Output: 50 40 30 20 10

📈 7. Example 4: Find Maximum and Minimum Values in an Array

#include <stdio.h>
int main() {
    int a[8];
    int i, max, min;

    printf("Please enter 8 integers:");
    for (i = 0; i < 8; i++) {
        scanf("%d", & a[i]);
    }

    max = min = a[0];
    for (i = 1; i < 8; i++) {
        if (a[i] > max) max = a[i];
        if (a[i] < min) min = a[i];
    }

    printf("Maximum value: %d\n", max);
    printf("Minimum value: %d\n", min);
    return 0;
}

✅ Skill Points:

Initial value set to the first element
Start comparing from the second element
Commonly used in IoT scenarios like “finding maximum temperature” or “finding brightest light intensity”

🧩 8. Example 5: Calculate Average of Sensor Data (IoT Application)

Simulate temperature sampling 5 times to find the average temperature:

#include <stdio.h>
int main() {
    float temp[5];
    float sum = 0;
    int i;

    printf("Please enter 5 temperature sampling values (unit: ℃):\n");
    for (i = 0; i < 5; i++) {
        scanf("%f", &temp[i]);
        sum += temp[i];
    }

    printf("Average temperature: %.2f℃\n", sum / 5);
    return 0;
}

📍 Extended Applications:

Can further calculate the temperature fluctuation range
Detect if it exceeds the safety threshold

⚙️ 9. Common Errors Summary

Error Type	Error Example	Description
Out of Bounds Access	`<span>a[5]</span>`	Maximum index is 4
Uninitialized	`<span>int a[5]; printf("%d", a[2]);</span>`	Value is undefined
Forgot to Add `<span>&</span>`	`<span>scanf("%d", a[i]);</span>`	Should be `<span>&a[i]</span>`
Index Type Error	`<span>for(float i=0;i<5;i++)</span>`	Index must be an integer

📌 Mnemonic:

Index starts from zero, last one is less by one. Input with address, out of bounds is most fatal.

✅ 10. Classroom Exercises (Solutions to be published tomorrow)

1️⃣ Input 10 numbers, find the average and count how many are greater than the average. 2️⃣ Input 5 student scores, output the results in reverse order. 3️⃣ Input a set of temperature data, output the maximum, minimum, and average temperature. 4️⃣ Write a program to count the number of odd and even numbers in the array.

🔜 Next Article Preview

📗 Advanced C Language Arrays – Array Sorting and Searching

Bubble Sort, Selection Sort

Array Searching (Sequential, Binary)

Practical Project: IoT Sampling Data Sorting Analysis

📚 IoT Smart Academy

A programming learning column designed for vocational IoT students. Ten minutes a day, from zero to project practice 🚀