Boundary Check

An index check prevents the program from reading outside an array.

boundary_check.c

#include <stdio.h>

int main(void) {
    int index = ;
    int values[3] = {10, 20, 30};
    int selected = -1;

    if (index >= 0 && index < 3) {
        selected = values[index];
    }

    printf("selected=%d\n", selected);
    return 0;
}

#include <stdio.h>

int main(void) {
    int index = ;
    int values[3] = {10, 20, 30};
    int selected = -1;

    if (index >= 0 && index < 3) {
        selected = values[index];
    }

    printf("selected=%d\n", selected);
    return 0;
}

#include <stdio.h>

int main(void) {
    int index = ;
    int values[3] = {10, 20, 30};
    int selected = -1;

    if (index >= 0 && index < 3) {
        selected = values[index];
    }

    printf("selected=%d\n", selected);
    return 0;
}

range guard The guard checks both lower and upper bounds before indexing.

fallback value The fallback path gives a predictable value for out-of-range input.