main.c

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

/* C is a statically typed language. That means you have to declare a
variable before its first use and state its type. In C variables should
be declared at the beginning of their scope. */

int main(int argc, char* argv[])
{
    /* the basic datatypes: */
    int a;         /* integer */
    float b;       /* floating point */
    double c;      /* double precision floating point*/
    char d;        /* character */

    int x = 5;     /* variables can be initialized on declaration*/
    int y, z;      /* these are several integers*/

    /* datatypes can be modified */
    signed int e;    /* positive and negative integers (=integers) */
    unsigned int f;  /* only non-negative integers but larger range */
    long int g;      /* larger range */
    short int h;     /* shorter range, less memory */
    /* full ist: https://en.wikipedia.org/wiki/C_data_types*/

    /* you can assign values to unitizialized and initialized variables later */
    x = 5;
    y = 6;
    b = 7.3f;            /* the 'f' stands for 'float'  */
    c = 7.3;             /* without f the number is treated as double*/
    z = x + y;           /* == 11 */
    z = x * y;           /* == 30 */
    z = x - y;           /* == -1 */
    z = x / y;           /* == 0,  because integer division is truncated */
    b = (float)x / y;    /* == 0.83333, because we made a typecast */

    x += 5;    /* equivalent to x = x + 5*; same for - * or / */
    x++;       /* equivalent to x = x+1; same for -; expression evaluates to x */
    ++x;       /* same as x++, but expression evaluates to x + 1 */

    c = 5.0 / 6.0;    /* gives 0.8333... */
    c = 0.78;         /* use dot to denote the comma */
    c = 0.78e7;       /* you can just use scientific notation */

    /* printing is a topic in its own */
    printf("x: %i\n", x);
    printf("b: %f\n", b);

    return 0;
}