Question

Need help with this C program based on threads. If someone could help as soon as possible thanks in advance.

Write a multi-threaded C program using pthread_create() according to the following instructions:

1. Your program should create exactly 2 new threads in the main() function, each of which invokes a different function. Print the thread IDs of the two new threads after they are created.

2. The first newly created thread invokes the following function

void *print_string_in_reverse_order(void *str)  {

      // this function accepts a string as an argument

      // it prints the string in reverse order

      // your code goes here

}

When this thread is created in the main() function, the argument passed to the function print_string_in_reverse_order() is the following string:

char * str = “Hello World!”;

3. The second newly created thread invokes the following function

void *print_in_uppercase_letters(void *str)  {

      // this function accepts a string as an argument

      // it prints the string in uppercase letters

      // your code goes here

}

When this thread is created in the main() function, the string argument passed to the function print_in_uppercase_letters() is a line of text typed by the user from keyboard.

Answer 1

The source code is followed by the output snapshot.

#include <stdio.h>
#include <pthread.h>

void *print_string_in_reverse_order(void *str) {
    // this function accepts a string as an argument
    // it prints the string in reverse order
    // your code goes here
    char *s = str;
    while(*s != '\0') s++; // go to end of string
    while(s != (char*)str)
        printf("%c", *--s);
    return NULL;
}

void *print_in_uppercase_letters(void *str) {
    // this function accepts a string as an argument
    // it prints the string in uppercase letters
    // your code goes here
    char *s = str;
    for(; *s != '\0'; s++)
    {
        if(*s >= 'a' && *s <= 'z')
            printf("%c", *s + 'A' - 'a');
        else
            printf("%c", *s);
    }
}

int main()
{
    pthread_t t1, t2;
    int ret;
    char * str = "Hello World!";
    char usrstr[200];

    scanf("%[^\n]s", usrstr);

    pthread_create(&t1, NULL, print_string_in_reverse_order, str);
    printf("Thread id 1: %lu\n", t1);

    pthread_create(&t2, NULL, print_in_uppercase_letters, usrstr);
    printf("Thread id 2: %lu\n", t2);

    //wait for threads to end
    pthread_join(t1, NULL);
    pthread_join(t2, NULL);
    printf("\n");
    return 0;
}