Making arrays user input specific for bubble sort? - c

Question

I'm learning to how to use command line arguments to get a number to decide how many elements are in an array to organize. The random number generator is supposed to take the user's number and generate that many random numbers, then sort them with the bubble sort.
But the number cannot be less than 2 or greater than 10,000.
I keep getting Segmentation fault (core dumped) or I'm able to enter any number (including a number less than 2 or greater than 10,000) and it does nothing.
I'm sure it is the first part of the code that is wrong, not the subprograms and definitions, but I don't know how to fix it.
#include <stdio.h>
int randu(void);
void bubble(int *, int);
void swap(int *, int *);
int main(int argc, char *argv[]) {
int num1;
if (argc<2) {
printf("Number must be between 2 and 10000.\n");
printf("Enter a number to sort.\n");
scanf("%d", &num1);
}
if (argc>10000) {
printf("Number must be between 2 and 10000.\n");
printf("Enter a number to sort.\n");
scanf("%d", &num1);
}
sscanf(argv[1], "%d", &num1);
int main(void) {
int x[num1], i;
for(i=0;i<num1;i++)
x[i]=randu();
printf("Here are %d numbers\n", num1);
for (i=0;i<num1;i++)
printf("%d\n",x[i]);
}
}
int randu(void) {
static int seed=17;
seed=(25179*seed+13849)%65536;
return seed;
}
void bubble(int a[], int num1){
int i,j;
for (i=0;i<num1-1;i++)
for(j=num1-1;i<j;j--)
if(a[j-1]>a[j])
swap(&a[j-1],&a[j]);
}
void swap(int *a, int *b){
int temp;
temp=*a;
*a=*b;
*b=temp;
}

Answer 1

There are a number of issues with your code
1) The use of argc is wrong. argc is not the value of an argument. It is the number of arguments (including program name).
2) There is a nested main inside main. Don't do that.
3) You never call the bubble sort function. Add it.
So a minor rewrite of your program:
int randu(void);
void bubble(int *, int);
void swap(int *, int *);
int main(int argc, char *argv[]) {
int num1;
if ((argc < 2) ||
(sscanf(argv[1], "%d", &num1) != 1) ||
(num1 < 2) ||
(num1 > 10000)) {
printf("You must give a number in range 2-10.000 as input\n");
return 0;
}
int x[num1], i;
for(i=0;i<num1;i++) {
x[i]=randu();
}
printf("Here are %d numbers\n", num1);
for (i=0;i<num1;i++) {
printf("%d\n",x[i]);
}
// Call the sort function
bubble(x, num1);
printf("Here are %d numbers sorted\n", num1);
for (i=0;i<num1;i++) {
printf("%d\n",x[i]);
}
return 0;
}
int randu(void) {
static int seed=17;
seed=(25179*seed+13849)%65536;
return seed;
}
void bubble(int a[], int num1){
int i,j;
for (i=0;i<num1-1;i++)
for(j=num1-1;i<j;j--)
if(a[j-1]>a[j])
swap(&a[j-1],&a[j]);
}
void swap(int *a, int *b){
int temp;
temp=*a;
*a=*b;
*b=temp;
}
"prog 5" gives the output:
Here are 5 numbers
48676
38117
52608
17049
29820
Here are 5 numbers sorted
17049
29820
38117
48676
52608