Jan Kończak

Exercise 1

int main(int argc, char *argv[]){
    return 0;
}

To compile, one may use any of:

• cc prog.c -o prog
• gcc   --std=c17 -Wall --pedantic -g -O2 x.c -o x
• clang --std=c17 -Wall --pedantic -g -O2 x.c -o x

Exercise 2

#include <stdio.h>
int main(int argc, char *argv[]){
    printf("Hello.\n");
    return 0;
}

#include <stdio.h>
int main(int argc, char *argv[]){
    fprintf(stdout, "Hello.\n");
    return 0;
}

#include <unistd.h>
int main(int argc, char *argv[]){
    write(STDOUT_FILENO, "Hello.\n", 7);
    return 0;
}

Exercise 3

#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[]){
    write(STDOUT_FILENO, argv[1], strlen(argv[1]));
    write(STDOUT_FILENO, "\n", 1);
    return 0;
}

Exercise 4

#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[]){
    write(STDOUT_FILENO, argv[1]+3, strlen(argv[1])-3);
    write(STDOUT_FILENO, "\n", 1);
    return 0;
}

Exercise 5

#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[]){
    for(int i = 0; i < argc; ++i){
        write(STDOUT_FILENO, argv[i], strlen(argv[i]));
        write(STDOUT_FILENO, "\n", 1);
    }
    return 0;
}

or, knowing that the argument array has a sentinel:

#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[]){
    do {
        write(STDOUT_FILENO, *argv, strlen(*argv));
        write(STDOUT_FILENO, "\n", 1);
    } while(*++argv);
    return 0;
}

Exercise 6

#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[]){
    char buffer[256];
    strncpy(buffer, argv[1], 254);
    buffer[254] = 0;
    strcat(buffer, "\n");
    write(STDOUT_FILENO, buffer, strlen(buffer));
    return 0;
}

Exercise 7

#include <unistd.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[]){
    size_t length = strlen(argv[1]);
    char *buffer = (char*) malloc(length+1);
    memcpy(buffer, argv[1], length);
    buffer[length]='\n';
    write(STDOUT_FILENO, buffer, strlen(buffer));
    free(buffer);
    return 0;
}

Exercise 8

#include <unistd.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[]){
    size_t length = strlen(argv[1]);
    char *buffer = (char*) malloc(length+1);
    for(int i = 0; i < length; ++i)
        buffer[i] = toupper(argv[1][i]);
    buffer[length]='\n';
    write(STDOUT_FILENO, buffer, length+1);
    free(buffer);
    return 0;
}

Exercise 9

#include <unistd.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[]){
    char buffer[256];
    scanf("%254[^\n]", buffer);
    strcat(buffer, "\n");
    write(STDOUT_FILENO, buffer, strlen(buffer));
    return 0;
}

#include <unistd.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[]){
    char buffer[256];
    fscanf(stdin, "%254[^\n]", buffer);
    strcat(buffer, "\n");
    write(STDOUT_FILENO, buffer, strlen(buffer));
    return 0;
}

#include <unistd.h>
int main(int argc, char *argv[]){
    char buffer[256];
    int length = read(STDIN_FILENO, buffer, 256);
    write(STDOUT_FILENO, buffer, length);
    return 0;
}

Exercise 10

#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv[]){
    char buffer[256];
    while(1){
        int length = read(STDIN_FILENO, buffer, 256);
        if(length == -1){
            perror(NULL);
            return 1;
        }
        if(length == 0)
            break;
        write(STDOUT_FILENO, buffer, length);
    }
    return 0;
}

Exercise 11

#include <unistd.h>
#include <stdio.h>
int readFile(){
    char buffer[256];
    while(1){
        int length = read(STDIN_FILENO, buffer, 256);
        if(length == -1){
            perror(NULL);
            return 1;
        }
        if(length == 0)
            return 0;
        write(STDOUT_FILENO, buffer, length);
    }
}
int main(int argc, char *argv[]){
    if(readFile())
        return -1;
    lseek(STDIN_FILENO, 0, SEEK_SET);
    if(readFile())
        return -1;
    return 0;
}

Exercise 12

#include <unistd.h>
#include <stdio.h>
int main(int argc, char *argv[]){
    char buffer[256];
    while(1){
        int length = read(4, buffer, 256);
        if(length == -1){
            perror(NULL);
            return 1;
        }
        if(length == 0)
            break;
        write(STDOUT_FILENO, buffer, length);
    }
    return 0;
}