C :

#include<stdio.h>
int main()
{
	int n,i,j;
	scanf("%d",&n);
	int a[n][n];
	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
			a[i][j]=0;
			if(i+j==n-1){
				a[i][j]=1;
			}
			
		}
	}
	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
			printf("%3d",a[i][j]);
		}
		printf("\n");
	} 
return 0;
}

C++ :

#include <iostream>
#include <iomanip>
#include <cmath>
#include <cstdio>

using namespace std;

int main(){
    int n,i,j,a[110][110];
    cin>>n;
    for(i=1;i<=n;i++){
    	for(j=1;j<=n;j++){
    		if(i+j!=n+1)
    		a[i][j]=0;
    		else
    		a[i][j]=1;
		}
	}
	for(i=1;i<=n;i++){
		for(j=1;j<=n;j++){
			cout<<setw(3)<<a[i][j];
		}
		
		cout<<endl;
	}
}

Python :

def getList(m,n):
    '''
      m 行数
      n 列数
      返回的是m行n列的二维数组，默认值为0
    '''
    ma = [ [0 for i in range(n)] for i in range(m) ]
    return ma
def printList(arr):
    for i in arr:
        for j in i:
            print('%3d' %(j),end='')
        print();
n=int(input())
arr = getList(n,n)
for i in range(0,n):
    for j in range(0,n):
        if i+j==n-1:
            arr[i][j] = 1
        # else:
        #     arr[i][j] = 0  #可加可不加  默认值为0
       
printList(arr)