Posix thread semaphore in linux

Question

I am trying to write a simple multithreaded program which has 6 threads performing 1. to read input from user 2. find length of string 3. find occurrence of character 4. count no. of vowels 5. count special characters 6. change case

except for the occurrence of character thread it is running as expected.but it doesnt allow me to enter the character to be looked and moves ahead to next part.

output-
      Converted Text:HIMANSHUSOURAV   //user input thread working correctly 
    length of text:15                //length working fine 
    Number of Vowels: 6              //count of vowels fine
     Number of Special characters: 0 // spl chars fine

but when the control reaches the counting no of occurences of a particular character( to be entered by user) in the existing input string (himanshusourav in this case) here the program without waiting for user to input the char to be found moves ahead and prints occurence as 0

o/p where error
 enter code here`enter the character whose occurence is
    to be counted in entered string:no of occurences of : 0

code:

#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<semaphore.h>
#include<string.h>

void *read();
void *changecase();
void *length();
void *vowel();
void *splchar();
void *findchar();

#define size 1024
 char buffer[size];

sem_t sem1,sem2,sem3,sem4,sem5,sem6;

void main(){
    int res;
    void *threadresult;
    pthread_t casethread,readthread,lengththread,vowelthread,splcharthread,findcharthread;
//Semaphore Creation
    res=sem_init(&sem5,0,0);
    res=sem_init(&sem1,0,0);
    res=sem_init(&sem2,0,0);
    res=sem_init(&sem3,0,0);
    res=sem_init(&sem4,0,0);
    res=sem_init(&sem6,0,0);


//Thread creation
    res=pthread_create(&readthread,NULL,read,NULL);
    if(res!=0){
        perror("Error While creating thread");
        exit(EXIT_FAILURE);
    }

    res=pthread_create(&casethread,NULL,changecase,NULL);
    if(res!=0){
        perror("Error While creating thread");
        exit(EXIT_FAILURE);
    }

    res=pthread_create(&lengththread,NULL,length,NULL);
    if(res!=0){
        perror("Error While creating thread");
        exit(EXIT_FAILURE);
    }

    res=pthread_create(&vowelthread,NULL,vowel,NULL);
    if(res!=0){
        perror("Error While creating thread");
        exit(EXIT_FAILURE);
    }

    res=pthread_create(&splcharthread,NULL,splchar,NULL);
    if(res!=0){
        perror("Error While creating thread");
        exit(EXIT_FAILURE);
    }

    res=pthread_create(&findcharthread,NULL,findchar,NULL);
    if(res!=0){
        perror("Error While creating thread");
        exit(EXIT_FAILURE);
    }

//Thread joining

    res=pthread_join(readthread,&threadresult);

    res=pthread_join(casethread,&threadresult);

    res=pthread_join(lengththread,&threadresult);

    res=pthread_join(splcharthread,&threadresult);

    res=pthread_join(vowelthread,&threadresult);

    //sem_post(&sem6);
}

void *read(){

    while(strncmp("quit",buffer,4)!=0){
        printf("\n\nEnter Text:");
        fgets(buffer,size,stdin);
        sem_post(&sem1);
        sleep(1);
//      sem_wait(&sem6);
    }
}


void *changecase(){
    int i;

    while(strncmp("quit",buffer,4)!=0){
        sem_wait(&sem1);    
        printf("\nConverted Text:");
        for(i=0;i<strlen(buffer);i++)
            printf("%c",toupper(buffer[i]));
        sem_post(&sem2);
        sleep(1);

    }
}

void *length(){
    int i;
    while(strncmp("quit",buffer,4)!=0){
        sem_wait(&sem2);
        printf("length of text:%d",strlen(buffer));
        sem_post(&sem3);
        sleep(1);
    }
}

void *vowel(){
    int i,vowels=0;
    while(strncmp("quit",buffer,4)!=0){
        sem_wait(&sem3);
        for(i=0;i<strlen(buffer);i++){
            if (buffer[i]=='a'|| buffer[i]=='e' || buffer[i]=='i' || buffer[i]=='o' || buffer[i]=='u')
                vowels++;
        }
        printf("\nNumber of Vowels: %d", vowels);
        vowels=0;
        sem_post(&sem4);
        sleep(1);
    }
}

void *splchar(){
    int i,splch=0;
    while(strncmp("quit",buffer,4)!=0){
        sem_wait(&sem4);
        for(i=0;i<strlen(buffer);i++){
            if(buffer[i]== '_' ||buffer[i]=='@' ||buffer[i]=='#' || buffer[i]=='*' || buffer[i]=='.')
                splch++;
        }
        printf("\nNumber of Special characters: %d\n",splch);
        splch=0;
        sem_post(&sem5);
        sleep(1);
    }
}


void *findchar(){
    int i,count;
 char ch[1];
    while(strncmp("quit",buffer,4)!=0){
        sem_wait(&sem5);
        count=0;
        printf("enter the character whose occurence is to be counted in entered string:");
        fgets(ch,1,stdin);
        for(i=0;i<strlen(buffer);i++){
            if(ch[1]==buffer[i])
                count++;
        }
    printf("\nno of occurences of %s: %d",ch,count);
//  sem_post(&sem6);
    sleep(1);
    }
}

Output on terminal

root@h2o-Vostro-1015:~/C/threads# gcc -o sem semsixthreads.c -lpthread root@h2o-Vostro-1015:~/C/threads# ./sem

Enter Text:himanshusourav

Converted Text:HIMANSHUSOURAV length of text:15 Number of Vowels: 6 Number of Special characters: 0 enter the character whose occurence is to be counted in entered string:no of occurences of : 0

Enter Text:himanshu_sourav

Converted Text:HIMANSHU_SOURAV length of text:16 Number of Vowels: 6 Number of Special characters: 1 enter the character whose occurence is to be counted in entered string:no of occurences of : 0

kindly advise...

Answer 1

A fgets call into a buffer with size 1 doesn't make sense in this case as only a NULL byte will be stored inside the buffer. The ch array should be at least two characters, and the the buffer contents checked against ch[0], not ch[1].

Answer 2

correct code would be

void *findchar(){
    int i,num;
    while(strncmp("quit",buffer,4)!=0){
        sem_wait(&sem5);            
        for(i=0;i<strlen(buffer);i++){
            if(ch[0]==buffer[i])
                num++;
        }
        printf("\nno. of occurences of %s: %d",ch,num);
        num=0;
        sleep(1);

    }
    pthread_exit("find char occurrence thread completed");
}

with user input part as

printf("enter the character whose occurence is to be counted in entered string:");
        fgets(ch,3,stdin);

and variable declaration as

char ch[5];