Data Types

Floating Point

double values store fractional numbers and are printed with floating-point formats.

double `double` is the usual C type for fractional numeric work.
format `%.2f` prints a floating-point value with two digits after the decimal point.

Floating Point

price
floating_point.c
Replay: real traced execution (multi-file project)
#include <stdio.h>

int main(void) {
    double price = 12.50;
    double taxRate = 0.08;
    double total = price + price * taxRate;

    printf("price=%.2f\n", price);
    printf("total=%.2f\n", total);
    return 0;
}

#include <stdio.h>

int main(void) {
    double price = 10.00;
    double taxRate = 0.08;
    double total = price + price * taxRate;

    printf("price=%.2f\n", price);
    printf("total=%.2f\n", total);
    return 0;
}

#include <stdio.h>

int main(void) {
    double price = 20.00;
    double taxRate = 0.08;
    double total = price + price * taxRate;

    printf("price=%.2f\n", price);
    printf("total=%.2f\n", total);
    return 0;
}

  1. price ← 12.5, taxRate ← 0.08, total ← 13.5

    3int main(void) {4    double price→ 12.5 = 12.50; //@price=10.00, 20.005    double taxRate→ 0.08 = 0.08;6    double total→ 13.5 = price12.5 + price * taxRate0.08;78    printf("price=%.2f\n", price12.5);9    printf("total=%.2f\n", total13.5);10    return 0;11}
    outputprice=12.50
total=13.50

  1. price ← 10, taxRate ← 0.08, total ← 10.8

    3int main(void) {4    double price→ 10 = 10.00;5    double taxRate→ 0.08 = 0.08;6    double total→ 10.8 = price10 + price * taxRate0.08;78    printf("price=%.2f\n", price10);9    printf("total=%.2f\n", total10.8);10    return 0;11}
    outputprice=10.00
total=10.80

  1. price ← 20, taxRate ← 0.08, total ← 21.6

    3int main(void) {4    double price→ 20 = 20.00;5    double taxRate→ 0.08 = 0.08;6    double total→ 21.6 = price20 + price * taxRate0.08;78    printf("price=%.2f\n", price20);9    printf("total=%.2f\n", total21.6);10    return 0;11}
    outputprice=20.00
total=21.60

Follow the Values

  1. price starts at 12.50.
  2. taxRate is 0.08.
  3. The tax is price * taxRate.
  4. total = price + price * taxRate becomes 13.50.
  5. The program prints price=12.50 and total=13.50. | price | taxRate | total | | --- | --- | --- | | 10.00 | 0.08 | 10.80 | | 12.50 | 0.08 | 13.50 | | 20.00 | 0.08 | 21.60 |

Exercise: floating_point.c

Reproduce total=13.50, then use price 10.00 and 20.00 to predict each total.