issues trying to make rows in c program - c

Question

#include <stdio.h>
int prime(int limit,int col);
int main(){
int limit,col,count,i;
printf("Table of Primes\n");
printf("===============\n");
printf("Upper limit: ");
scanf("%d",&limit);
getchar();
printf("# of columns: ");
scanf("%d",&col);
count=prime( limit,col);
return 0;
}
int prime(int limit,int col){
int i,j,w;
for(w=0;w<col;w++){
for(i=2;i<=limit;i++){
for(j=2;j<=i;j++){
if(i%j==0){
break;
}
}
if(i==j){
printf("%d ",i);
}
}
printf("\n");
}
}
The code above is to find the amount of prime numbers between 2 and the user input numbers.
I have that working fine, but my issue is getting the Code to be put into columns (defined by # of columns)
I talked this over with my teacher and she said that I do not have to use a 2D array to accomplish this.
Can anyone please help me out?
Also the output is spouse to look like this:
Table of Primes
===============
Upper limit: 175
# of columns: 5
2 3 5 7 11
13 17 19 23 29
31 37 41 43 47
53 59 61 67 71
73 79 83 89 97
101 103 107 109 113
127 131 137 139 149
151 157 163 167 173
Thank you.

Answer 1

You can easily test the number of columns and print a newline. The function prime() also lacked a return value so I return w as the number of primes found. This is just a slight tweak to your prime() function.
#include <stdio.h>
#include <string.h>
int prime(int limit, int col) {
int i, j, w = 0;
for (i=2; i<=limit; i++) {
for (j=2; j<=i; j++) {
if (i%j == 0) {
break;
}
}
if (i==j) {
if (w++ % col == 0) // test number of columns
printf("\n");
printf("%7d", i); // specify field width
}
}
printf("\n");
return w;
}
int main(void) {
prime (173, 5);
return 0;
}
Program output:
2 3 5 7 11
13 17 19 23 29
31 37 41 43 47
53 59 61 67 71
73 79 83 89 97
101 103 107 109 113
127 131 137 139 149
151 157 163 167 173
I leave you to add the frills.

Answer 2

I suggest you to make separate functions for finding primes and displaying primes, so you will have more control on displaying those primes:
#include <stdio.h>
#include <math.h> // sqrt
int is_prime (int x);
void prime(int limit, int col);
int main ()
{
int limit, col;
printf("Table of Primes\n");
printf("===============\n");
printf("Upper limit: ");
scanf("%d",&limit);
getchar();
printf("# of columns: ");
scanf("%d",&col);
prime(limit, col);
printf("\n");
return 0;
}
int is_prime (int num)
{
int flag;
int i;
double p;
p = sqrt(num);
flag = 1;
if (num == 1)
return 0;
if (num == 2)
return flag;
if ((num % 2) == 0)
return 0;
for (i = 3; i <= p; i += 2)
{
if ((num % i) == 0)
{
flag = false;
return flag;
}
}
return flag;
}
void prime (int limit, int column)
{
int i, j, cnt;;
cnt = 0;
for (i = 0; i < limit; i++) {
if (is_prime(i)) {
printf("%4d ", i);
cnt++;
if ((cnt % column) == 0) {
printf("\n");
}
}
}
}
Of course you can change is_prime to your own function.

Answer 3

You can keep a variable to count how many numbers have been printed, then count % col will be zero every time count is a multiple of col, so this would work
#include <stdio.h>
void prime(int limit, int col);
int readint(const char *const message);
int main()
{
int limit,col;
printf("Table of Primes\n");
printf("===============\n");
limit = readint("Upper limit");
col = readint("# of columns");
prime(limit, col);
return 0;
}
int readint(const char *const message)
{
int value;
printf("%s> ", message);
while (scanf("%d", &value) != 1)
{
int chr;
printf("\tinvalid input\n");
printf("%s> ", message);
do {
chr = getchar();
} while ((chr != EOF) && (chr != '\n'));
}
return value;
}
void prime(int limit, int col)
{
int i, j;
int count;
count = 0;
for (i = 2 ; i <= limit ; i++)
{
for (j = 2 ; j <= i ; j++)
{
if (i % j == 0)
break;
}
if (i == j)
{
count += 1;
printf("%5d", i);
if ((count != 0) && (count % col == 0))
printf("\n");
}
}
}
Note that your code does not handle invalid input, I added that in this code, many people erroneously ignore scanf()'s return value, which is there for a reason.