Data Types

Booleans

stdbool.h provides the bool, true, and false names for clear yes/no state.

stdbool `#include <stdbool.h>` defines `bool`, `true`, and `false`.
ternary The ternary operator chooses one of two values based on a condition.

Booleans

enabled
booleans.c
Replay: real traced execution (multi-file project)
#include <stdbool.h>
#include <stdio.h>

int main(void) {
    bool enabled = true;
    const char *label = enabled ? "enabled" : "disabled";

    printf("flag=%s\n", label);
    return 0;
}

#include <stdbool.h>
#include <stdio.h>

int main(void) {
    bool enabled = false;
    const char *label = enabled ? "enabled" : "disabled";

    printf("flag=%s\n", label);
    return 0;
}

  1. enabled ← 1, label ← enabled

    4int main(void) {5    bool enabled→ 1 = true; //@enabled=false6    const char *label→ enabled = enabled1 ? "enabled" : "disabled";78    printf("flag=%s\n", labelenabled);9    return 0;10}
    outputflag=enabled

  1. enabled ← 0, label ← disabled

    4int main(void) {5    bool enabled→ 0 = false;6    const char *label→ disabled = enabled0 ? "enabled" : "disabled";78    printf("flag=%s\n", labeldisabled);9    return 0;10}
    outputflag=disabled

Follow the Flag

  1. enabled starts as true.
  2. The ternary checks enabled.
  3. Because it is true, label becomes enabled.
  4. The program prints flag=enabled. | enabled | label | output | | --- | --- | --- | | true | enabled | flag=enabled | | false | disabled | flag=disabled |

Exercise: booleans.c

Reproduce flag=enabled, then use enabled=false to predict the flag output.