#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <semaphore.h>
#include <string.h>
        
#define THREAD_NUM 2

FILE *fp;

//Declaring new linenumber to identify its whose turn to sing
int lineNumber = 0;
int sing(int singer_id){
        int read, len=0;
        char *line=NULL;
        char *token;

        read = getline(&line, &len,fp); 
        if(read!=-1){
                printf("singer[%d]: ", singer_id);
                token = strtok(line," ");
                while( token != NULL){
                        printf("%s ", token);
                        fflush(stdout);
                        token = strtok(NULL, " ");
                        usleep(500000);
                } 
                
                //increasing line number by one to give another singer a chance
                lineNumber++;
                printf("\n");
        }
        lineNumber = -1;
        if(line) free(line);
        return read;
        
}

void *turnA(void *param)
{
    //creating semaphore
    sem_t *mySem = (sem_t *) param;
    //until lines are finished
    while (lineNumber != -1) {
        //if this is even line singer 0 will sing
        if (lineNumber % 2 == 0) {
            sing(0);
            //waiting
            sem_wait(mySem);
        }
        sem_getvalue(mySem, &lineNumber);
    }     
}

void *turnB(void *param)
{
    //creating semaphore
    sem_t *mySem = (sem_t *) param;
    //until lines are finished
    while (lineNumber != -1) {
        //if its odd line singer 1 will sing
        if (lineNumber % 2 == 1) {
            sing(1);
            //waiting
            sem_wait(mySem);
        }
        sem_getvalue(mySem, &lineNumber);
    }   
}

int main()
{
    sem_t mySem;
        int i;
        pthread_t tid[THREAD_NUM]; /* the thread identifier */
        pthread_attr_t attr; /* set of attributes for the thread */

        fp = fopen("input.txt","r");
        if(fp== NULL){
                printf("File open error\n");
                return;
        }

        /* get the default attributes */
        pthread_attr_init(&attr);

        /* create the thread */
        pthread_create(&tid[0],&attr,turnA, &mySem);
        pthread_create(&tid[1],&attr,turnB, &mySem);

        /* now wait for the thread to exit */
        for (i=0;i<THREAD_NUM;i++)
                pthread_join(tid[i],NULL);
        fclose(fp);

        printf("Parent Done\n");
}

C Language online compiler

Write, Run & Share C Language code online using OneCompiler's C online compiler for free. It's one of the robust, feature-rich online compilers for C language, running the latest C version which is C18. Getting started with the OneCompiler's C editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose language as 'C' and start coding!

Read inputs from stdin

OneCompiler's C online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.

#include <stdio.h>
int main()
{
    char name[50];
    printf("Enter name:");
    scanf("%s", name);
    printf("Hello %s \n" , name );
    return 0;
    
}

About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}