Variables and Arithmetic

My Second Program (1)

fahrenheit-while.c
#include <stdio.h>

/* Fahrenheit/Celsius Table
   0 - 300, step 20 */
int main(void)
{
    int fahr, celsius;
    int lower = 0, upper = 300, step = 20;

    fahr = lower;
    while (fahr <= upper) {
        celsius = 5 * (fahr - 32) / 9;
        printf("%d\t%d\n", fahr, celsius);
        fahr = fahr + step;
    }

    return 0;
}

My Second Program (2)

/* ... */

Comment (can span multiple lines)

 
int fahr, celsius;

  • Variable definition

  • Must come at the beginning of a block

 
int lower = 0, upper = 300, step = 20;

Variable definition and initialization

My Second Program (3)

while (fahr <= upper) {
    ...
}

  • Loop: “While condition holds, execute body”

  • Condition: fahr is less or equal upper

 
celsius = 5 * (fahr - 32) / 9;

Usual arithmetic (expression) ⟶ usual operator precedence rules

  • Careful: integer division brutally truncates decimal places!

  • More natural but always 0: 5/9 * (fahr-32)

My Second Program (4)

printf("%d\t%d\n", fahr, celsius);

  • Formatted output

  • ⟶ number of arguments can vary (?)

  • “%d” obviously means “integer”

  • Important: printf() is not part of the core language, but rather an ordinary library function

  • ⟶ standard library

More Datatypes

int

Integer, nowadays mostly 32 bits wide

float

Floating point number, mostly 32 bit

char

Single character (one byte, generally)

short

Smaller integer

double

double precision variant of float

  • Width and precision of all datatypes is machine dependent!

  • Compound datatypes: arrays, structures, … (⟶ later)