C random matrix with numbers between 0 and 9 - c

Question

I'm a C newbie and I'm trying to make a matrix 5x4 only with numbers between 0 and 9 where each number needs to be there 2 times (I'm trying to make the memory game). I got this code but I think that this is quite a mess and its not working, so my question is, how can I improve my code or how can I make this matrix in a different way?
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#define MaxC 4
#define MaxL 5
int main(){
int n1=0, n2=0, n3=0, n4=0, n5=0, n6=0, n7=0, n8=0, n9=0, n0=0;
int i=0,j=0,r;
int n[MaxL][MaxC];
srand(time(NULL));
while(i<5){
j=0;
while(j<4){
r=(rand()%10);
if(r==0 && n0<2){
n0++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==1 && n1<2){
n1++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==2 && n2<2){
n2++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==3 && n3<2){
n3++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==4 && n4<2){
n4++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==5 && n5<2){
n5++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==6 && n6<2){
n6++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==7 && n7<2){
n7++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==8 && n8<2){
n8++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
if(r==9 && n9<2){
n9++;
j++;
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
}
i++;
}
return 0;
}

Answer 1

Here is a little change to make your program shorter.
I've placed n0, n1, .... into an array indexed by r.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MaxC 4
#define MaxL 5
int main()
{
int na[10] = {0};
int n[MaxL][MaxC], i=0;
srand((unsigned)time(NULL));
while(i<MaxL)
{
int j=0;
while(j<MaxC)
{
int r = rand() % 10;
if(na[r]<2)
{
++na[r];
n[i][j] = r;
printf(" %3d ",n[i][j]);
++j;
}
}
++i;
printf("\n");
}
return 0;
}
Example output:
2 6 1 8
4 7 0 2
5 3 7 8
9 1 0 3
5 6 4 9
Your code keeps trying random number until you have had each number twice. That is not the best approach.
Instead you could initialize the matrix with the 20 numbers at fix locations and then do a random shuffle of the matrix.

Answer 2

First off, you've placed j++ in every if statement. It'll look a lot cleaner if you just leave j++ at the end of the loop. Same goes for the print statement.
Second, if you could post what the program is printing out or describe how it's not working, that would help you get an answer to your problem. I don't see what functional issue your code has without trying it myself.
EDIT: See 4386427's answer for further ways to simplify your code.

Answer 3

May I help you? You can simplify your code if you replace ten the nX variables on array. Look at this:
int main(){
int c[10] = {0};
int i=0,j=0,r;
int n[MaxL][MaxC];
srand(time(NULL));
for(i = 0; i < 5; i++) {
for(j = 0; j < 4; j++) {
do {
r=(rand()%10);
} while( c[r] > 2);
++c[r];
n[i][j]=r;
printf(" %3d ",n[i][j]);
}
printf("\n");
}
return 0;
}