How to print diagonal star pattern in C

This will work fine !! :)

#include<iostream>
using namespace std;


int main()
{
    int n,m=0;
    int m2=0;
    cin>>n;
    int f=-1,l=n;
    for(int i=0;i<n;i++)
    {
        f=f+1;
        l=l-1;
        
        for(int j=0;j<n;j++)
        {
            if(j==f || j==l) cout<<"*";
            else cout<<" ";
        }
        
        cout<<endl;
    }
}

To not change any code and answer your question "what goes in the if"

n - 1 - i == j || j == i

this does

The pattern consists of exactly n * 2 - 1 rows and columns. So you can run an outer loop to iterate through rows with structure for(i=1; i<= count; i++); where count = n * 2 - 1. Each row contains exactly n * 2 - 1 columns. So, run inner loop as for(j=1; j<=count; j++). And inside this loop we need stars to be printed when row and column number both are equal (i.e. print star whenever if(i == j)) and if(j == count - i + 1). For example:

#include <stdio.h>

int main() {
  int i, j, n;
  int count;

  printf("Enter n: ");
  scanf("%d", &n);

  count = n * 2 - 1;

  for (i = 1; i <= count; i++) {
    for (j = 1; j <= count; j++) {
      if (j == i || (j == count - i + 1)) {
        printf("*");
      } else {
        printf(" ");
      }
    }

    printf("n");
  }

  return 0;
}