Data Types & Variables

1#include <stdio.h>
2#include <limits.h>  // Contains INT_MIN, INT_MAX
3
4int main() {
5    // Integer declarations
6    int age = 25;
7    int negative = -100;
8    int count = 0;
9    
10    // Display values
11    printf("Age: %d\n", age);
12    printf("Negative: %d\n", negative);
13    printf("Count: %d\n", count);
14    
15    // Size of int on this system
16    printf("\nSize of int: %zu bytes (%zu bits)\n", sizeof(int), sizeof(int) * 8);
17    
18    // Range of int (from limits.h)
19    printf("INT_MIN: %d\n", INT_MIN);
20    printf("INT_MAX: %d\n", INT_MAX);
21
22    return 0;
23}

1#include <stdio.h>
2#include <float.h>  // Contains FLT_MIN, FLT_MAX
3
4int main() {
5    // Float declarations (use 'f' suffix)
6    float price = 99.99f;
7    float temperature = -40.5f;
8    float pi = 3.14159f;
9    
10    // Double for more precision (default for decimals)
11    double precise_pi = 3.14159265358979;
12    
13    // Display values
14    printf("Price: %.2f\n", price);
15    printf("Temperature: %.1f\n", temperature);
16    printf("Pi (float): %.6f\n", pi);
17    printf("Pi (double): %.14f\n", precise_pi);
18    
19    // Size comparison
20    printf("\nSize of float: %zu bytes (%zu bits)\n", sizeof(float), sizeof(float) * 8);
21    printf("Size of double: %zu bytes (%zu bits)\n", sizeof(double), sizeof(double) * 8);
22    
23    // Range of float (from float.h)
24    printf("\nFLT_MIN: %e\n", FLT_MIN);
25    printf("FLT_MAX: %e\n", FLT_MAX);
26    
27    return 0;
28}

1#include <stdio.h>
2
3int main() {
4    // Character declarations (use single quotes!)
5    char letter = 'A';
6    char digit = '5';
7    char symbol = '@';
8    char newline = '\n';
9    
10    // Characters are stored as numbers (ASCII)
11    printf("Letter: %c (ASCII: %d)\n", letter, letter);
12    printf("Digit: %c (ASCII: %d)\n", digit, digit);
13    printf("Symbol: %c (ASCII: %d)\n", symbol, symbol);
14    
15    // Character arithmetic works!
16    char next = letter + 1;  // 'A' + 1 = 'B'
17    printf("Next letter: %c\n", next);
18    
19    // Convert uppercase to lowercase
20    char lower = letter + 32;  // 'A' + 32 = 'a'
21    printf("Lowercase: %c\n", lower);
22    
23    // Size of char
24    printf("\nSize of char: %zu byte (%zu bits)\n", sizeof(char), sizeof(char) * 8);
25    
26    return 0;
27}

1#include <stdio.h>
2
3int main() {
4    // Array - collection of integers
5    int scores[3] = {85, 90, 78};
6    
7    // String - array of characters
8    char name[] = "Alice";
9    
10    // Printing
11    printf("Name: %s\n", name);
12    printf("First score: %d\n", scores[0]);
13    
14    return 0;
15}

1#include <stdio.h>
2
3int main() {
4    // Integer format specifiers
5    int num = 42;
6    printf("Decimal:     %d\n", num);    // 42
7    printf("Octal:       %o\n", num);    // 52
8    printf("Hexadecimal: %x\n", num);    // 2a
9    printf("Hexadecimal: %X\n", num);    // 2A
10    
11    // Floating-point format specifiers
12    float pi = 3.14159f;
13    printf("Default:     %f\n", pi);     // 3.141590
14    printf("2 decimals:  %.2f\n", pi);   // 3.14
15    printf("Scientific:  %e\n", pi);     // 3.141590e+00
16    
17    // Character and string
18    char ch = 'A';
19    char name[] = "Alice";
20    printf("Character:   %c\n", ch);     // A
21    printf("String:      %s\n", name);   // Alice
22    
23    // Width and alignment
24    printf("Right align: %10d\n", num);  //         42
25    printf("Left align:  %-10d|\n", num);// 42        |
26    printf("Zero pad:    %05d\n", num);  // 00042
27    
28    // Special
29    printf("Address:     %p\n", &num);   // 0x7ffd...
30    printf("Percent:     100%%\n");      // 100%
31    
32    return 0;
33}

1#include <stdio.h>
2
3int main() {
4    // === DECLARATION ===
5    int count;              // Declaration only (garbage value!)
6    float temperature;      // Not initialized
7    char letter;            // Contains random data
8    
9    // === INITIALIZATION (Recommended!) ===
10    int age = 25;           // Declare + initialize
11    float price = 19.99f;   // 'f' suffix for float
12    char grade = 'A';       // Single quotes for char
13    
14    // === ASSIGNMENT (After Declaration) ===
15    count = 100;            // Now has a value
16    temperature = 36.5f;
17    letter = 'X';
18    
19    // === MULTIPLE DECLARATIONS ===
20    int x, y, z;                    // All are int
21    int a = 1, b = 2, c = 3;        // All initialized
22    float width = 10.5f, height = 20.0f;
23    
24    // === DISPLAY VALUES ===
25    printf("Age: %d\n", age);
26    printf("Price: $%.2f\n", price);
27    printf("Grade: %c\n", grade);
28    printf("Dimensions: %.1f x %.1f\n", width, height);
29    
30    return 0;
31}

1#include <stdio.h>
2#include <stdlib.h>  // For NULL
3
4int main() {
5    // Initializing with "null" or zero values
6    int count = 0;           // Integer zero
7    float total = 0.0f;      // Float zero
8    double amount = 0.0;     // Double zero
9    char empty = '\0';       // Null character
10    int *pointer = NULL;     // Null pointer
11    
12    // Check for zero/null values
13    if (count == 0) {
14        printf("Count is zero\n");
15    }
16    
17    if (empty == '\0') {
18        printf("Character is null (ASCII 0)\n");
19    }
20    
21    if (pointer == NULL) {
22        printf("Pointer is NULL\n");
23    }
24    
25    return 0;
26}

1#include <stdio.h>
2
3// === #define MACROS (Before main, no semicolon!) ===
4#define MAX_SIZE 100
5#define PI 3.14159
6#define GREETING "Hello, World!"
7#define SQUARE(x) ((x) * (x))   // Macro with parameter
8
9int main() {
10    // === const VARIABLES ===
11    const int maxAge = 120;
12    const float taxRate = 0.08f;
13    const char grade = 'A';
14    
15    // Using #define constants
16    printf("Max Size: %d\n", MAX_SIZE);
17    printf("PI: %f\n", PI);
18    printf("%s\n", GREETING);
19    printf("5 squared: %d\n", SQUARE(5));
20    
21    // Using const variables
22    printf("Max Age: %d\n", maxAge);
23    printf("Tax Rate: %.2f%%\n", taxRate * 100);
24    printf("Grade: %c\n", grade);
25    
26    // ERROR: Cannot modify constants!
27    // maxAge = 150;     // Compiler error!
28    // MAX_SIZE = 200;   // Compiler error!
29    
30    return 0;
31}