#include<stdio.h>
int main()
{
    int a;
    scanf("%d",&a);
    int i,j,k;
    i = a;
    while ( i<=a+3 ){
        j = a;
        while ( j<=a+3 ){
            while ( k<=a+3 ){
                if (i!=j ){
                    if( i!=k ){
                        if ( j!=k ){
                            printf("%d%d%d",i,j,k);
                        }
                    }
                }
                k++;
            }
            j++;
        }
        i++;
    }
    return 0;
}
      

我少打了一个k = a;

#include<stdio.h>
int main()
{
    int a;
    scanf("%d",&a);
    int i,j,k;
    i = a;
    while ( i<=a+3 ){
        j = a;
        while ( j<=a+3 ){
            while ( k<=a+3 ){//大概看了一下，k没赋值，怎么能比较呢？因为你没有发出题目不好做出判断。也许在这之前有一句：k=a;
                if (i!=j ){
                    if( i!=k ){
                        if ( j!=k ){
                            printf("%d%d%d",i,j,k);
                        }
                    }
                }
                k++;
            }
            j++;
        }
        i++;
    }
    return 0;
}

嗯嗯

的确，我看了半天才找出来的，还是大佬强