C

Example

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/* =========================
   ENUM
   ========================= */

enum Gender {
    MALE = 1,
    FEMALE = 2
};

/* =========================
   STRUCT
   ========================= */

struct Student {
    char name[50];
    int age;
    float grade;
    enum Gender gender;
};

/* =========================
   FUNCTION PROTOTYPES
   ========================= */

void printStudent(struct Student s);
void changeAge(struct Student *s, int newAge);
void changeGrade(struct Student *s, float newGrade);

int add(int a, int b);
void swap(int *a, int *b);

void saveStudent(struct Student s);
void readFile(void);


/* =========================
   MAIN
   ========================= */

int main(void)
{
    /* -------------------------
       BASIC TYPES
       ------------------------- */

    int age = 20;
    float height = 1.75f;
    double price = 99.99;
    char letter = 'A';

    const int MAX_AGE = 120;

    printf("=== BASIC TYPES ===\n");

    printf("Age: %d\n", age);
    printf("Height: %.2f\n", height);
    printf("Price: %.2f\n", price);
    printf("Letter: %c\n", letter);

    printf("\n=== SIZEOF ===\n");

    printf("int    = %zu bytes\n", sizeof(int));
    printf("float  = %zu bytes\n", sizeof(float));
    printf("double = %zu bytes\n", sizeof(double));
    printf("char   = %zu byte\n", sizeof(char));

    printf("MAX_AGE = %d\n", MAX_AGE);


    /* -------------------------
       POINTER
       ------------------------- */

    printf("\n=== POINTER ===\n");

    int number = 10;

    int *ptr = &number;

    printf("number = %d\n", number);
    printf("*ptr   = %d\n", *ptr);
    printf("address = %p\n", (void *)ptr);

    /* Change number through pointer */

    *ptr = 50;

    printf("number after *ptr = 50: %d\n", number);


    /* -------------------------
       STRING FUNCTIONS
       ------------------------- */

    printf("\n=== STRINGS ===\n");
    // string functions have safer version with the `strn` prefix

    char name1[50] = "Alice";
    char name2[50];

    /* strcpy */

    strcpy(name2, name1);

    /* Safer bounded copy */
    // strncpy(destination, source, sizeof(destination) - 1);
    // destination[sizeof(destination) - 1] = '\0';

    printf("name1 = %s\n", name1);
    printf("name2 = %s\n", name2);

    /* strlen */

    printf("Length of name1 = %zu\n", strlen(name1));

    /* strcmp */

    if (strcmp(name1, name2) == 0) {
        puts("name1 and name2 are equal.");
    } else {
        puts("name1 and name2 are different.");
    }


    /* -------------------------
       SCANF
       ------------------------- */

    printf("\n=== INPUT ===\n");

    printf("Enter your age: ");
    scanf("%d", &age);

    printf("You entered: %d\n", age);


    /* -------------------------
       ENUM + SWITCH
       ------------------------- */

    printf("\n=== ENUM + SWITCH ===\n");

    enum Gender gender = MALE;

    switch (gender) {

        case MALE:
            puts("Gender: Male");
            break;

        case FEMALE:
            puts("Gender: Female");
            break;

        default:
            puts("Unknown");
            break;
    }


    /* -------------------------
       STRUCT
       ------------------------- */

    printf("\n=== STRUCT ===\n");

    struct Student student;

    strcpy(student.name, "John");
    student.age = 21;
    student.grade = 15.5f;
    student.gender = MALE;

    printStudent(student);


    /* -------------------------
       FUNCTION WITH STRUCT POINTER
       ------------------------- */

    printf("\n=== FUNCTION + STRUCT POINTER ===\n");

    changeAge(&student, 25);
    changeGrade(&student, 18.0f);

    printStudent(student);


    /* -------------------------
       NORMAL FUNCTION
       ------------------------- */

    printf("\n=== FUNCTION ===\n");

    int result;

    result = add(10, 20);

    printf("10 + 20 = %d\n", result);


    /* -------------------------
       FUNCTION WITH POINTERS
       ------------------------- */

    printf("\n=== FUNCTION + POINTERS ===\n");

    int a = 10;
    int b = 20;

    printf("Before swap: a=%d b=%d\n", a, b);

    swap(&a, &b);

    printf("After swap:  a=%d b=%d\n", a, b);


    /* -------------------------
       ARRAY / TABLE
       ------------------------- */

    printf("\n=== TABLE ===\n");

    int numbers[5] = {
        10,
        20,
        30,
        40,
        50
    };

    for (int i = 0; i < 5; i++) {
        printf("numbers[%d] = %d\n", i, numbers[i]);
    }


    /* -------------------------
       MALLOC
       ------------------------- */

    printf("\n=== MALLOC ===\n");

    int size = 5;

    int *dynamicNumbers;

    dynamicNumbers = malloc(size * sizeof(int));

    if (dynamicNumbers == NULL) {
        puts("Memory allocation failed.");
        return 1;
    }

    for (int i = 0; i < size; i++) {
        dynamicNumbers[i] = (i + 1) * 10;
    }

    for (int i = 0; i < size; i++) {
        printf("%d ", dynamicNumbers[i]);
    }

    printf("\n");

    free(dynamicNumbers);

    dynamicNumbers = NULL;


    /* -------------------------
       RAND
       ------------------------- */

    printf("\n=== RANDOM ===\n");

    /* Initialize random generator */

    srand((unsigned int)time(NULL));

    for (int i = 0; i < 5; i++) {

        int randomNumber = rand() % 100;

        printf("Random number: %d\n", randomNumber);
    }


    /* -------------------------
       FILE
       ------------------------- */

    printf("\n=== FILE ===\n");

    saveStudent(student);

    readFile();


    printf("\nProgram finished.\n");

    return 0;
}


/* =========================
   FUNCTION: ADD
   ========================= */

int add(int a, int b)
{
    return a + b;
}


/* =========================
   FUNCTION: SWAP
   ========================= */

void swap(int *a, int *b)
{
    int temp;

    temp = *a;
    *a = *b;
    *b = temp;
}


/* =========================
   FUNCTION: PRINT STRUCT
   ========================= */

void printStudent(struct Student s)
{
    printf("Name: %s\n", s.name);
    printf("Age: %d\n", s.age);
    printf("Grade: %.2f\n", s.grade);
}


/* =========================
   FUNCTION: MODIFY STRUCT
   ========================= */

void changeAge(struct Student *s, int newAge)
{
    s->age = newAge;
}


/* =========================
   FUNCTION: MODIFY GRADE
   ========================= */

void changeGrade(struct Student *s, float newGrade)
{
    s->grade = newGrade;
}


/* =========================
   SAVE STRUCT TO FILE
   ========================= */

void saveStudent(struct Student s)
{
    FILE *file;

    /* Open file for writing */

    file = fopen("student.txt", "w");

    if (file == NULL) {
        puts("Could not open file.");
        return;
    }

    fprintf(file, "Name: %s\n", s.name);
    fprintf(file, "Age: %d\n", s.age);
    fprintf(file, "Grade: %.2f\n", s.grade);

    /* Close file */

    fclose(file);

    puts("Student saved to student.txt");
}


/* =========================
   READ FILE
   ========================= */

void readFile(void)
{
    FILE *file;

    char line[100];

    /* Open file for reading */

    file = fopen("student.txt", "r");

    if (file == NULL) {
        puts("Could not open file.");
        return;
    }

    puts("\nFile content:");

    while (fgets(line, sizeof(line), file) != NULL) {
        printf("%s", line);
    }

    /* Go to beginning */

    rewind(file);

    /* Move to the end */

    fseek(file, 0, SEEK_END);

    /* Get current position */

    long position = ftell(file);

    printf("\nFile size: %ld bytes\n", position);

    /* Close */

    fclose(file);
}

Compilation

gcc main.c -o main.out -Wall

Online C

• Online C by France-IOI