Testing and Debugging

Assert Condition

A checked condition can protect the line that depends on it.

precondition A precondition is a fact the next operation needs before it is safe.
checked path Checking the condition first lets the program report the problem instead of using a bad value.

Assert Condition

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

int main(void) {
    int value = 6;
    int ok = value > 0;

    if (ok) {
        int quotient = 120 / value;
        printf("ok=%d quotient=%d\n", ok, quotient);
    } else {
        printf("ok=%d quotient=skipped\n", ok);
    }

    return 0;
}

#include <stdio.h>

int main(void) {
    int value = 0;
    int ok = value > 0;

    if (ok) {
        int quotient = 120 / value;
        printf("ok=%d quotient=%d\n", ok, quotient);
    } else {
        printf("ok=%d quotient=skipped\n", ok);
    }

    return 0;
}

#include <stdio.h>

int main(void) {
    int value = 10;
    int ok = value > 0;

    if (ok) {
        int quotient = 120 / value;
        printf("ok=%d quotient=%d\n", ok, quotient);
    } else {
        printf("ok=%d quotient=skipped\n", ok);
    }

    return 0;
}

  1. value ← 6, ok ← 1

    3int main(void) {4    int value→ 6 = 6; //@value=0, 105    int ok→ 1 = value6 > 0;

  2. quotient ← 20

    7if (ok1) {8    int quotient→ 20 = 120 / value6;9    printf("ok=%d quotient=%d\n", ok1, quotient20);10} else {
    outputok=1 quotient=20

  3. return 0;

    14    return 0;15}

  1. value ← 0, ok ← 0

    3int main(void) {4    int value→ 0 = 0;5    int ok→ 0 = value0 > 0;

  2. else

    9    printf("ok=%d quotient=%d\n", ok, quotient);10} else {11    printf("ok=%d quotient=skipped\n", ok0);12}
    outputok=0 quotient=skipped

  3. return 0;

    14    return 0;15}

  1. value ← 10, ok ← 1

    3int main(void) {4    int value→ 10 = 10;5    int ok→ 1 = value10 > 0;

  2. quotient ← 12

    7if (ok1) {8    int quotient→ 12 = 120 / value10;9    printf("ok=%d quotient=%d\n", ok1, quotient12);10} else {
    outputok=1 quotient=12

  3. return 0;

    14    return 0;15}