Data Types & Variables

1#include <stdio.h>
2
3int main() {
4    int age = 25;
5    int score = 100;
6    int temperature = -10;
7    
8    printf("Age: %d years\n", age);
9    printf("Score: %d points\n", score);
10    printf("Temperature: %d degrees\n", temperature);
11    
12    // Simple calculation
13    int sum = age + score;
14    printf("Age + Score = %d\n", sum);
15    
16    return 0;
17}

1#include <stdio.h>
2
3int main() {
4    double price = 19.99;
5    double discount = 0.20;  // 20% off
6    
7    // Calculate discounted price
8    double savings = price * discount;
9    double final_price = price - savings;
10    
11    printf("Original Price: $%.2f\n", price);
12    printf("Discount (20%%): $%.2f\n", savings);
13    printf("Final Price: $%.2f\n", final_price);
14    
15    return 0;
16}

1#include <stdio.h>
2
3int main() {
4    char first = 'J';     // First initial
5    char middle = 'K';    // Middle initial
6    char last = 'R';      // Last initial
7    
8    printf("Initials: %c.%c.%c.\n", first, middle, last);
9    
10    // Characters are numbers! (ASCII codes)
11    printf("'A' as number: %d\n", 'A');  // 65
12    printf("'a' as number: %d\n", 'a');  // 97
13    
14    // Character math
15    char next = 'A' + 1;  // B (65 + 1 = 66)
16    printf("Letter after A: %c\n", next);
17    
18    return 0;
19}

1#include <stdio.h>
2#include <stdbool.h>  // For C99-C17
3
4int main() {
5    bool isRaining = false;
6    bool hasUmbrella = true;
7    
8    printf("Is it raining? %d\n", isRaining);     // 0 (false)
9    printf("Have umbrella? %d\n", hasUmbrella);   // 1 (true)
10    
11    // Use in conditions
12    if (isRaining && !hasUmbrella) {
13        printf("You'll get wet!\n");
14    } else {
15        printf("You're fine!\n");
16    }
17    
18    return 0;
19}

1#include <stdio.h>
2#include <stdint.h>  // For fixed-width types
3
4int main() {
5    // Exact sizes - works the same on ANY computer!
6    int8_t tiny = 100;         // Exactly 1 byte
7    int32_t normal = 1000000;  // Exactly 4 bytes
8    uint64_t big = 9000000000; // Exactly 8 bytes (unsigned)
9    
10    // Great for colors (0-255 each)
11    uint8_t red = 255;
12    uint8_t green = 128;
13    uint8_t blue = 0;
14    
15    printf("Color: RGB(%d, %d, %d)\n", red, green, blue);
16    printf("Big number: %llu\n", big);
17    
18    return 0;
19}

1#include <stdio.h>
2#include <stddef.h>  // or <stdlib.h>
3
4int main() {
5    int numbers[5] = {10, 20, 30, 40, 50};
6    
7    // size_t for array sizes and loop counters
8    size_t length = sizeof(numbers) / sizeof(numbers[0]);
9    
10    printf("Array has %zu elements:\n", length);  // %zu for size_t
11    
12    for (size_t i = 0; i < length; i++) {
13        printf("  numbers[%zu] = %d\n", i, numbers[i]);
14    }
15    
16    return 0;
17}

1// C23 Example (requires -std=c23)
2#include <stdio.h>
3
4int main() {
5    // bool is now a keyword!
6    bool isReady = true;
7    
8    // nullptr for pointers (safer than NULL)
9    int *ptr = nullptr;
10    
11    if (ptr == nullptr) {
12        printf("Pointer is null\n");
13    }
14    
15    // typeof - copy the type of another variable
16    int x = 42;
17    typeof(x) y = 100;  // y is also an int
18    
19    printf("x = %d, y = %d\n", x, y);
20    
21    return 0;
22}

1#include <stdio.h>
2
3int main() {
4    // Create a variable named "age" and store 25 in it
5    int age = 25;
6    
7    // Print the value stored in "age"
8    printf("Your age is: %d\n", age);
9    
10    // Change the value (variable = can change!)
11    age = 26;
12    printf("Next year: %d\n", age);
13    
14    return 0;
15}

1// Declaring variables (reserving space in memory)
2int age;            // An integer named "age"
3double salary;      // A double named "salary"
4char initial;       // A character named "initial"
5
6// Declaring multiple variables of the same type
7int x, y, z;        // Three integers
8float width, height; // Two floats

1#include <stdio.h>
2
3int main() {
4    // Create and initialize variables
5    int age = 25;
6    double price = 19.99;
7    char grade = 'A';
8    
9    printf("Before:\n");
10    printf("  Age: %d, Price: $%.2f, Grade: %c\n", age, price, grade);
11    
12    // Change the values
13    age = 26;           // Birthday!
14    price = 24.99;      // Price went up
15    grade = 'B';        // Grade changed
16    
17    printf("After:\n");
18    printf("  Age: %d, Price: $%.2f, Grade: %c\n", age, price, grade);
19    
20    return 0;
21}

1#include <stdio.h>
2
3#define TAX_RATE 0.08   // 8% tax (no semicolon!)
4
5int main() {
6    const double PRICE = 100.0;  // Can't change this!
7    
8    double tax = PRICE * TAX_RATE;
9    double total = PRICE + tax;
10    
11    printf("Price: $%.2f\n", PRICE);
12    printf("Tax (8%%): $%.2f\n", tax);
13    printf("Total: $%.2f\n", total);
14    
15    // PRICE = 200.0;  // ERROR! Can't change a const
16    
17    return 0;
18}

1#include <stdio.h>
2
3int main() {
4    printf("=== Size of Data Types (in bytes) ===\n\n");
5    
6    // Integer types
7    printf("char:       %zu byte\n", sizeof(char));
8    printf("short:      %zu bytes\n", sizeof(short));
9    printf("int:        %zu bytes\n", sizeof(int));
10    printf("long:       %zu bytes\n", sizeof(long));
11    printf("long long:  %zu bytes\n", sizeof(long long));
12    
13    printf("\n");
14    
15    // Floating-point types
16    printf("float:       %zu bytes\n", sizeof(float));
17    printf("double:      %zu bytes\n", sizeof(double));
18    printf("long double: %zu bytes\n", sizeof(long double));
19    
20    printf("\n");
21    
22    // Size of a variable
23    int age = 25;
24    printf("Variable 'age': %zu bytes\n", sizeof(age));
25    
26    return 0;
27}