I need to understand this program.

Code:

---

#include<stdio.h>
main()
{
  int i,j;
  for(i=1;i<=4;i++)
  {
      for(j=1;j<=4-i;j++)
      {
          printf(" ");
      }
      for(j=1;j<=2*i-1;j++)
      {
          printf("*");
      }
      printf("\n");
  }

---

Have you tried running it?

Perhaps go though and rename the lousy variable names with something better, say
for ( rowNumber = 1;rowNumber <=4;rowNumber ++)