read_age.c

Compile with: gcc -g -Wall -std=c11 -o read_age read_age.c

#include <stdio.h>
#include <stdlib.h>

int main() {
  int age;
  printf("What is your age? ");
  scanf("%d", &age);
  printf("You are %d years old\n", age);
}

corrupt_mem.c

#include <stdlib.h>

int main(int argc, char** argv) {
  int a[2];
  int* b = malloc(2*sizeof(int));
  int* c;

  a[2] = 5;
  b[0] += 2;
  c = b+3;
  free(&(a[0]));
  free(b);
  free(b);
  b[0] = 5;

  return EXIT_SUCCESS;
}

leaky.c

Compile with: gcc -g -Wall -std=c11 -o leaky leaky.c

Use valgrind to check:

valgrind ./leaky
valgrind --leak-check=full ./leaky

#include <stdio.h>
#include <stdlib.h>
#define LEN 5

int main() {
  int* ptr1 = malloc(LEN * sizeof(int));
  int* ptr2 = calloc(LEN, sizeof(int));

  printf("%d\n", ptr1[0]);  // Undefined behavior!
  printf("%d\n", ptr2[0]);  // OK, initialized to 0 by calloc

  free(ptr1);
}