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The C programming language made simple

Communicating between processes using signals

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> int x = 0; void handle_sigusr(int sig) { if (x == 0) { printf("(HINT) Remember that multiplication is repetitive addition!\n"); } } int main(int argc, char* argv[]) { int pid = fork(); if (pid == -1) { return 1; } if (pid == 0) { // Child process sleep(5); kill(getppid(), SIGUSR1); } else { // Parent process struct sigaction sa; sa.sa_flags = SA_RESTART; sa.sa_handler = &handle_sigusr; sigaction(SIGUSR1, &sa, NULL); printf("What is the result of 3 x 5?: "); scanf("%d\n", &x); if (x == 15) { printf("Right!\n"); } else { printf("Wrong\n"); } wait(NULL); } return 0; }