C - Calculating statistical values from command line using multithreaded programing - c

Question

I'm a beginner working on a C practice program that can calculate various statistical values for a list of numbers read in from the command line. But when trying to compile my code in Linux, I get a handful of errors that I'm not sure how to interpret, and was wondering if I could get some help from those more familiar with the C language than myself. I've included both my code and the errors below.
My code:
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
int *values;
int size;
double avg=0.0;
int minValue=0;
int maxValue=0;
void *runAvg(void *param);
void *runMin(void *param);
void *runMax(void *param);
int main (int argc, char *argv[]){
if(argc != 2){
fprintf(stderr, "usage: %s <integer value>\n", argv[0]);
}
int i;
for(i=1; i < argc; i++){
values=&(atoi(argv[i]));
size++;
}
pthread_t avgPt[size];
pthread_t minPt[size];
pthread_t maxPt[size];
pthread_attr_t attr;
//create threads
pthread_create(&avgPt, &attr, runAvg, values);
pthread_create(&minPt, &attr, runMin, values);
pthread_create(&maxPt, &attr, runMax, values);
//wait for threads to exit
pthread_join(avgPt, NULL);
pthread_join(minPt, NULL);
pthread_join(maxPt, NULL);
//print results of threads
printf("\n Average: %f \n",avg);
printf("\n Minimum: %d \n",minValue);
printf("\n Maximum: %d \n",maxValue);
}
void *runAvg(void *param){
int sum=0;
int i=0;
int *values;
values=(int*)param;
for(i=0;i<size; i++) sum += values[i];
avg = sum / (double)size;
pthread_exit(0);
}
void *runMin(void *param){
int i=0;
int *values;
values=(int*)param;
minValue = values[0];
for(i=0;i<size;i++){
if(values[i]<minValue){
minValue=values[i];
}
}
pthread_exit(0);
}
void *runMax(void *param){
int i=0;
int *values;
values=(int*)param;
maxValue=values[0];
for(i=0;i<size;i++){
if(values[i] > maxValue){
maxValue = values[i];
}
}
pthread_exit(0);
}
My compile errors:
423assign.c:20: error: lvalue required as unary ‘&’ operand
423assign.c:30: warning: passing argument 1 of ‘pthread_create’ from
incompatible pointer type
/usr/include/pthread.h:227: note: expected ‘pthread_t * __restrict__’
but argument is of type ‘pthread_t (*)[(unsigned int)(size)]’
423assign.c:31: warning: passing argument 1 of ‘pthread_create’ from
incompatible pointer type
/usr/include/pthread.h:227: note: expected ‘pthread_t * __restrict__’
but argument is of type ‘pthread_t (*)[(unsigned int)(size)]’
423assign.c:32: warning: passing argument 1 of ‘pthread_create’ from
incompatible pointer type
/usr/include/pthread.h:227: note: expected ‘pthread_t * __restrict__’
but argument is of type ‘pthread_t (*)[(unsigned int)(size)]’
423assign.c:34: warning: passing argument 1 of ‘pthread_join’ makes
integer from pointer without a cast
/usr/include/pthread.h:244: note: expected ‘pthread_t’ but argument is
of type ‘pthread_t *’
423assign.c:35: warning: passing argument 1 of ‘pthread_join’ makes
integer from pointer without a cast
/usr/include/pthread.h:244: note: expected ‘pthread_t’ but argument is
of type ‘pthread_t *’
423assign.c:36: warning: passing argument 1 of ‘pthread_join’ makes
integer from pointer without a cast
/usr/include/pthread.h:244: note: expected ‘pthread_t’ but argument is
of type ‘pthread_t *’

Answer 1

Your thread functions were okay.
One issue was not allocating an int array to contain the values from atoi.
Also, your pthread_t variables should not be arrays. And your attr value is never initialized and not used.
Here's a cleaned up version with the bugs annotated and fixed [please pardon the gratuitous style cleanup]:
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
int *values;
int size;
double avg = 0.0;
int minValue = 0;
int maxValue = 0;
void *runAvg(void *param);
void *runMin(void *param);
void *runMax(void *param);
int
main(int argc, char **argv)
{
// NOTE/BUG: this should be "< 2" and not "!= 2"
if (argc < 2) {
fprintf(stderr, "usage: %s <integer value>\n", argv[0]);
exit(1);
}
int i;
--argc;
++argv;
// NOTE/BUG: we must allocate an int array of sufficient size
values = calloc(argc,sizeof(int));
for (i = 0; i < argc; i++) {
values[i] = atoi(argv[i]);
size++;
}
// NOTE/BUG: these should _not_ be arrays
pthread_t avgPt;
pthread_t minPt;
pthread_t maxPt;
// NOTE/BUG: this is unitialized and it's not set to anything, so the
// pthread_create 2nd argument can [and should be] NULL
#if 0
pthread_attr_t attr;
#endif
// create threads
#if 0
pthread_create(&avgPt, &attr, runAvg, values);
pthread_create(&minPt, &attr, runMin, values);
pthread_create(&maxPt, &attr, runMax, values);
#else
pthread_create(&avgPt, NULL, runAvg, values);
pthread_create(&minPt, NULL, runMin, values);
pthread_create(&maxPt, NULL, runMax, values);
#endif
// wait for threads to exit
pthread_join(avgPt, NULL);
pthread_join(minPt, NULL);
pthread_join(maxPt, NULL);
// print results of threads
printf("\n Average: %f \n", avg);
printf("\n Minimum: %d \n", minValue);
printf("\n Maximum: %d \n", maxValue);
}
void *
runAvg(void *param)
{
int sum = 0;
int i = 0;
int *values;
values = param;
for (i = 0; i < size; i++)
sum += values[i];
avg = sum / (double) size;
return (void *) 0;
}
void *
runMin(void *param)
{
int i = 0;
int *values;
values = param;
minValue = values[0];
for (i = 0; i < size; i++) {
if (values[i] < minValue)
minValue = values[i];
}
return (void *) 0;
}
void *
runMax(void *param)
{
int i = 0;
int *values;
values = param;
maxValue = values[0];
for (i = 0; i < size; i++) {
if (values[i] > maxValue)
maxValue = values[i];
}
return (void *) 0;
}