I'm attempting to work with functions for the first time in C. I'm trying to write a classic roll the dice game that rolls a die 10,000 times and then prints out how many times each number has been rolled using functions.
In the code below I keep getting the error code "Expected expression" when trying to set result= roll_die (int num_sides);. It says that it's occurring on the int. When I remove int I get the error code "Use of undeclared identifier 'num_sides' ". How can I fix this?
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int roll_die(int num_sides){
num_sides = rand() % 6;
num_sides = num_sides + 1;
return num_sides;
}
int main(void)
{
srand((int)time(0));
unsigned int counter, result, num1=0, num2=0, num3=0, num4=0, num5=0, num6=0;
unsigned int num_rolls = 10000;
for(counter=0; counter<=num_rolls; counter++)
{
result = roll_die (num_sides);
if(result==1)
num1++;
else if(result==2)
num2++;
else if(result==3)
num3++;
else if(result==4)
num4++;
else if(result==5)
num5++;
else if(result==6)
num6++;
else{
printf("Error occurred. \n"); return 0;
}
}
printf("Number of 1s rolled: %d \n", num1);
printf("Number of 2s rolled: %d \n", num2);
printf("Number of 3s rolled: %d \n", num3);
printf("Number of 4s rolled: %d \n", num4);
printf("Number of 5s rolled: %d \n", num5);
printf("Number of 6s rolled: %d \n", num6);
}
As I noted in comments, you need either to replace num_sides in main() with 6, or you need to define and initialize a variable (int num_sides = 6;). Your function hard-codes 6 as the number of sides and ignores the value passed in (it just uses the parameter as a local variable, ignoring what it was supplied as a value).
Fixing these two issues leads to code like this:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
static int roll_die(int num_sides)
{
int result = rand() % num_sides + 1;
return result;
}
int main(void)
{
srand((int)time(0));
unsigned int counter, result, num1 = 0, num2 = 0, num3 = 0, num4 = 0, num5 = 0, num6 = 0;
unsigned int num_rolls = 10000;
for (counter = 0; counter <= num_rolls; counter++)
{
result = roll_die(6);
if (result == 1)
num1++;
else if (result == 2)
num2++;
else if (result == 3)
num3++;
else if (result == 4)
num4++;
else if (result == 5)
num5++;
else if (result == 6)
num6++;
else
{
printf("Error occurred. \n");
return 0;
}
}
printf("Number of 1s rolled: %d \n", num1);
printf("Number of 2s rolled: %d \n", num2);
printf("Number of 3s rolled: %d \n", num3);
printf("Number of 4s rolled: %d \n", num4);
printf("Number of 5s rolled: %d \n", num5);
printf("Number of 6s rolled: %d \n", num6);
}
Example output:
Number of 1s rolled: 1670
Number of 2s rolled: 1653
Number of 3s rolled: 1656
Number of 4s rolled: 1687
Number of 5s rolled: 1696
Number of 6s rolled: 1639
You should also use an array instead of the 6 numX variables. For example, using int num[7] = { 0 }; would allow you to use the value returned by roll_die() as an index into the array. That compresses the code like this:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
static int roll_die(int num_sides)
{
return rand() % num_sides + 1;
}
int main(void)
{
srand(time(0));
unsigned num[7] = { 0 };
unsigned num_rolls = 10000;
int num_sides = 6;
for (unsigned counter = 0; counter <= num_rolls; counter++)
num[roll_die(num_sides)]++;
for (int i = 1; i <= num_sides; i++)
printf("Number of %ds rolled: %d \n", i, num[i]);
return 0;
}
Sample output – can you spot any difference from the previous output other than that due to the different random sequence? There shouldn't be any!
Number of 1s rolled: 1705
Number of 2s rolled: 1651
Number of 3s rolled: 1653
Number of 4s rolled: 1616
Number of 5s rolled: 1631
Number of 6s rolled: 1745
And this makes it easy to generalize for N-sided dice, like this:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
static int roll_die(int num_sides)
{
return rand() % num_sides + 1;
}
int main(int argc, char **argv)
{
int num_sides = 6;
if (argc == 2)
{
num_sides = strtol(argv[1], 0, 0);
if (num_sides < 2 || num_sides > 999)
{
fprintf(stderr, "Number of sides of %d is not in the range 2..999\n", num_sides);
exit(EXIT_FAILURE);
}
}
srand(time(0));
unsigned num[num_sides + 1];
for (int i = 1; i <= num_sides; i++)
num[i] = 0;
unsigned num_rolls = 10000;
for (unsigned counter = 0; counter <= num_rolls; counter++)
num[roll_die(num_sides)]++;
for (int i = 1; i <= num_sides; i++)
printf("Number of %ds rolled: %d \n", i, num[i]);
return 0;
}
And, if this program is called die83, then a sample run might look like:
$ ./die83 8
Number of 1s rolled: 1294
Number of 2s rolled: 1197
Number of 3s rolled: 1256
Number of 4s rolled: 1228
Number of 5s rolled: 1230
Number of 6s rolled: 1222
Number of 7s rolled: 1278
Number of 8s rolled: 1296
$