C Programming Building Blocks¶

#include <stdio.h>

int main(int argc, char *argv[]) {
    int int_variable;
    float float_variable;

    int_variable = 10;
    float_variable = 10.10;

    printf("The value of the integer variable is %d\n", int_variable);
    printf("The value of my float variable is %f\n", float_variable);
}

#include <stdio.h>

int main(int argc, char *argv[]) {
    char char_value;
    char_value = 'c';
    printf("The value of my character datatype is %c\n", char_value);

    int i = 0;
    for (i = 0; i <128; i++) {
        char_value = (char) i;
        printf("The value of my character datatype is %c for the integer value %d \n", char_value, i);
    }
}

#include<stdio.h>

int main(int argc, char *argv[]) {
    char s[]  = {'s', 't', 'r', 'i', 'n', 'g', '\0'};
    printf("%s\n", s);

    char s1[10];
    int i, j;
    for (i = 65, j = 0; i < 70; i++) {
        s1[j] = (char) i;
        j++;
    }
    s1[j] = '\0';

    printf("%s\n", s1);

    char s2[] = "string";

    printf("%s\n", s2);

}

#include <stdio.h>

int main() {
    printf("size of a short is %d\\n", sizeof(short));
    printf("size of a int is %d\\n", sizeof(int));
    printf("size of a long is %d\\n", sizeof(long));
}

#include <stdio.h>

int main(void) {

    int j, k;
    int *ptr;
    j = 1;
    k = 2;
    ptr = &k;
    printf("\n");
    printf("j has the value %d and is stored at %p\n", j, (void *) &j);
    printf("k has the value %d and is stored at %p\n", k, (void *) &k);
    printf("ptr has the value %p and is stored at %p\n", ptr, (void *) &ptr);
    printf("The value of the integer pointed to by ptr is %d\n", *ptr);

    return 0;
}

#include <stdio.h>


int main(void) {

    int my_array[] = {1, 23, 17, 4, -5, 100};
    int *ptr;
    int i;
    ptr = &my_array[0];
    printf("\n\n");
    for (i = 0; i < 6; i++) {
        printf("my_array[%d] = %d   ", i, my_array[i]);
        printf("ptr + %d = %d\n", i, *(ptr + i));
    }
    return 0;
}

#include <stdio.h>

int main(void) {

    char strA[80] = "A string to be used for demonstration purposes";
    char strB[80];

    char *pA;     /* a pointer to type character */
    char *pB;     /* another pointer to type character */
    puts(strA);   /* show string A */
    pA = strA;    /* point pA at string A */
    puts(pA);     /* show what pA is pointing to */
    pB = strB;    /* point pB at string B */
    putchar('\n');       /* move down one line on the screen */
    while (*pA != '\0')   /* line A (see text) */
    {
        *pB++ = *pA++;   /* line B (see text) */
    }
    *pB = '\0';          /* line C (see text) */
    puts(strB);          /* show strB on screen */
    return 0;
}

#include <stdio.h>

#define ROWS 5
#define COLS 10

int multi[ROWS][COLS];

int main(void) {
    int row, col;
    for (row = 0; row < ROWS; row++) {
        for (col = 0; col < COLS; col++) {
            multi[row][col] = row * col;
        }
    }

    for (row = 0; row < ROWS; row++) {
        for (col = 0; col < COLS; col++) {
            printf("\n%d  ", multi[row][col]);
            printf("%d ", *(*(multi + row) + col));
        }
    }

    return 0;
}

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

int main(int argc, char *argv[]) {
    struct tag {
        char lname[20];
        char fname[20];
        int age;
        float rate;
    };

    struct tag my_struct;

    strcpy(my_struct.lname, "Kumaran");
    strcpy(my_struct.fname, "Senthil");

    printf("\n%s ", my_struct.fname);
    printf("%s\n", my_struct.lname);

    return 0;
}

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

struct tag {                     /* the structure type */
    char lname[20];             /* last name */
    char fname[20];             /* first name */
    int age;                    /* age */
    float rate;                 /* e.g. 12.75 per hour */
};

struct tag my_struct;           /* define the structure */
void show_name(struct tag *p);  /* function prototype */

int main(void) {
    struct tag *st_ptr;         /* a pointer to a structure */
    st_ptr = &my_struct;        /* point the pointer to my_struct */
    strcpy(my_struct.lname, "Jensen");
    strcpy(my_struct.fname, "Ted");
    printf("\n%s ", my_struct.fname);
    printf("%s\n", my_struct.lname);
    my_struct.age = 63;
    show_name(st_ptr);          /* pass the pointer */
    return 0;
}

void show_name(struct tag *p) {
    printf("\n%s ", p->fname);  /* p points to a structure */
    printf("%s ", p->lname);
    printf("%d\n", p->age);
}

#include <stdio.h>

#define ROWS 5
#define COLS 10

int main(int argc, char *argv[]) {
    int multi[ROWS][COLS];

    int row, col;

    for (row = 0; row < ROWS; row++) {
        for (col = 0; col < COLS; col++) {
            multi[row][col] = row * col;
        }
    }

    for (row = 0; row < ROWS; row++) {
        for (col = 0; col < COLS; col++) {
            printf("\n%d ", multi[row][col]);
            printf("%d ", *(*(multi + row) + col));
        }
    }
}

#ifndef MY_PROGRAM_HEADER
#define MY_PROGRAM_HEADER

#define SQUARE(x) ((x) * (x))
#define WINDOWS 1
#define LINUX 2
#define PLATFORM LINUX

#include <stdio.h>

int main(int argc, char *argv[]) {
    int num = 20;
    printf("Square of the number is %d\n", SQUARE(num));

    // Conditinal Compilation

#ifdef PLATFORM
#if PLATFORM == WINDOWS
    printf("Compiling for Windows\n");
#define PATH_SEPARATOR "\\"
#elif PLATFORM == LINUX
    printf("Compiling for Linux\n");
#endif
#define PATH_SEPARATOR "/"
#else
#error Platform not defined!
#endif

}

#endif // MY_PROGRAM_HEADER

#include <stdio.h>

union Data {
    int i;
    float f;
    char str[20];
};

int main(int argc, char *argv[]) {
    union Data data;
    union Data *ptr;

    ptr = &data;

    data.i  = 42;
    printf("Integer value: %d \n", data.i);

    ptr->f = 3.14;
    printf("Float value: %f\n", data.f);

    printf("Integer value again: %d \n", data.i);
    printf("Since Union share memory, the integer value is lost.");
}

#include <stdio.h>
#include <limits.h>

/**
 * %b specifier is available since C23
 * https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2630.pdf
 * if %b is not available for your compiler
 * we can use print_bin to see the binary
 **/

void print_bin(unsigned char byte)
{
    int i = CHAR_BIT; /* however many bits are in a byte on your platform */
    while(i--) {
        putchar('0' + ((byte >> i) & 1)); /* loop through and print the bits */
    }
}

int main(int argc, char *argv[]) {
    unsigned char a = 12 ; // Binary 00001100
    unsigned char b = 10;  // Binary 00001010

    printf("Original Values: \n");
    printf("a = %d (Binary: %08b)\n", a, a);
    printf("b = %d (Binary: %08b)\n", b, b);

    printf("Decimal %d in Binary is", a);
    print_bin(a);

    printf("\n");

    printf("Decimal %d in Binary is", b);
    print_bin(b);

    // Bitwise AND (&)
    printf("\n Bitwise AND (&): \n");
    printf("%d & %d = %d (binary: %08b)\n", a, b, a & b, a & b);


    // Bitwise OR (|)
    printf("\n Bitwise OR (|): \n");
    printf("%d | %d = %d (binary: %08b)\n", a, b, a | b, a | b);

    // Bitwise XOR (^)
    printf("\n Bitwise XOR (^): \n");
    printf("%d ^ %d = %d (binary: %08b)\n", a, b, a ^b, a ^b);

    // Left shift <<
    printf("\n Left Shift (<<): \n");
    printf("%d << 1 = %d (binary: %08b)\n", a, a << 1, a << 1);

    // Right shift >>
    printf("\n Right Shift (>>): \n");
    printf("%d >> 1 = %d (binary: %08b)\n", a, a >> 1, a >> 1);

    // Bitwise NOT (~)
    printf("\n Bitwise NOT (~) \n");
    printf("~%d = %d (binary: %08b)\n", a, (unsigned char) ~a, (unsigned char)~a);
}

#include <stdio.h>
#include "other.h"

// Declare the external variable
extern int shared_value;        // This tells compiler variable is defined elsewhere
extern void modify_value(void); // Declare external function

int main(int argc, char *argv[]) {
    printf("Initial shared value: %d\n", shared_value);


    // Modify the value in main
    shared_value = 20;
    printf("After modifying the value in main: %d\n", shared_value);


    modify_value();
    printf("After calling modify_value: %d\n", shared_value);

    return 0;
}

#ifndef LEARNTOSOLVEIT_OTHER_H
#define LEARNTOSOLVEIT_OTHER_H

#include <stdio.h>
int shared_value = 10;

void modify_value(void) {
    shared_value *= 2;
    printf("Modified in other.h : %d\n", shared_value);
}

#endif //LEARNTOSOLVEIT_OTHER_H

#include<stdio.h>
#include "config.h"

/**
 * $ gcc p18_extern_config.c config.c -o p18_extern_config
 * $ ./p18_extern_config
 * Max connections: 100
 **/

int main(int argc, char *argv[]) {
    init_config();
    printf("Max connections: %d\n", app_config.max_connections);
    return 0;
}

#ifndef LEARNTOSOLVEIT_CONFIG_H
#define LEARNTOSOLVEIT_CONFIG_H

extern struct Config {
    int max_connections;
    char *server_name;
    int port;
} app_config;

extern void init_config(void);
#endif //LEARNTOSOLVEIT_CONFIG_H

#include "config.h"

struct Config app_config = {
        .max_connections = 100,
        .server_name = "localhost",
        .port = 8080
};

void init_config(void) {
    // Initialize configuration
}

#include <stdio.h>


enum DayOfWeek {
    SUNDAY = 1,
    MONDAY,
    TUESDAY,
    WEDNESDAY,
    THURSDAY,
    FRIDAY,
    SATURDAY
};

enum TaskStatus {
    PENDING, // Will start at 0
    IN_PROGRESS,
    COMPLETED,
    CANCELLED
};

int main(int argc, char *argv[]) {
    enum DayOfWeek today = WEDNESDAY;
    printf("Day number of the week %d\n", today);


    enum TaskStatus status = PENDING;
    printf("\nTask Status: \n");
    printf("Initial Status: %d\n", status);

    status = COMPLETED;
    printf("Updated status: %d\n", status);

    if (status == COMPLETED) {
        printf("Task is Complete!\n");
    }

    return 0;
}

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

#define COLS 5


int main(int argc, char *argv[]) {

    typedef int RowArray[COLS];
    RowArray *rptr;

    int nrows = 10;
    int row, col;

    rptr = malloc(nrows * COLS * sizeof(int));

    for (row = 0; row < nrows; row++) {
        for (col = 0; col < COLS; col++) {
            rptr[row][col] = row * col;
        }
    }

    free(rptr);
    return 0;
}