// Old-style error handling in C

int function1() {               // return integer is a boolean for success: 1=true=OK, 0=false=error
  return 1;
}

int function2() {
  return 1;
}

int function3() {
  return 0;         
}

void function4(int *error) {   // call-by-reference parameter is an indication for errors
                               // 0=OK, positive=error
                               // the actual number represents the type of error 
  *error = 0;
}

void function5(int *error) {
  *error = 0;
}

void function6(int *error) {
  *error = 49;
}

int main(int argc, char *argv[]) {
int error;
 
  if (function1())                    // boolean return type indicates success/failure
    if (function2())                  // note the cascading of ifs, not very convenient
      if (function3())
        printf("all functions OK\n");
      else
        printf("error: function3\n");
    else
      printf("error: function2\n");
  else
    printf("error: function1\n");

  function4(&error);                  // call-by-reference error code indicates success/failure
  if (!error) {                       // again cascading
    function5(&error);
    if (!error) {
      function6(&error);
      if (!error)
        printf("all functions OK\n");
    }
  }
  if (error)
    printf("error: %d\n",error);
}