ExpressionCompiler

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <string.h>
#include <sys/wait.h>

#define ER(number) {          \
    printf("E%d\n", number);  \
    exit(-1);                 \
}

#define MAXLEN 5000

int main() {
    umask(0000);
    int fd = creat("program.c", 0666);
    if (fd < 0) ER(1);

    char* init = "#include <stdio.h>\n int main() { printf(\"%d\\n\", (";
    size_t initlen = strlen(init);
    if (write(fd, init, initlen) != initlen) ER(2);

    char input[MAXLEN];
    fgets(input, MAXLEN, stdin);
    size_t inputlen = strlen(input);
    if (write(fd, input, inputlen) != inputlen) ER(3);

    char* fin = ")); return 0; }";
    size_t finlen = strlen(fin);
    if (write(fd, fin, finlen) != finlen) ER(4);
    if (close(fd) < 0) ER(45);

    int res = fork();

    if (res > 0) {

        int* wstatus;
        wait(wstatus);

        int res1 = fork();

        if (res1 > 0) {

            int* wstatus1;
            wait(wstatus1);

            if (unlink("program.out") < 0) ER(46);
            if (unlink("program.c") < 0) ER(47);
        }
        else if (res1 == 0) {

            execlp("./program.out", "./program.out", 0);
            ER(5);
        }
        else if (res1 < 0) ER(6);
    }
    else if (res == 0) {

        execlp("gcc", "gcc", "program.c", "-o", "program.out", 0);
        ER(9);
    }
    else if (res < 0) ER(10);

    return 0;
}