c-error-codes.c

const int ERROR = 1;
const int SUCCESS = 0;

int compute(int input, int* output) {
  if (cond(input)) {
    return ERROR;
  } else {
    *output = computeOutput(input);
    return SUCCESS;
  }
}

// Usage
int output;
int input;

if (int error = compute(input, &output)) {
  error_handler(error);
}