1.倒推法实现输出杨辉三角有半部分，代码如下:

 1 #include<stdio.h> 2 int main() 3 { 4     int n,i,j,a[100]; 5     printf("请输入行数n:"); 6     scanf("%d",&n); 7     printf("  1"); 8     printf("\n"); 9     a[1]=a[2]=1;10     printf("%3d%3d\n",a[1],a[2]);11     for(i=3;i<=n;i++)12     {13         a[1]=a[i]=1;14         for(j=i-1;j>1;j--)15             a[j]=a[j]+a[j-1];16         for(j=1;j<=i;j++)17             printf("%3d",a[j]);18         printf("\n");19     }20     return 0;21 }

运行结果:

2.实现输出杨辉三角全部，代码如下:

 1 #include<stdio.h> 2 int main() 3 { 4     int a[10][21]; 5     int i,j; 6     for(i=0;i<10;i++) 7         for(j=0;j<21;j++) 8             a[i][j]=0; 9             a[0][10]=1;10     for(i=1;i<10;i++)11         for(j=10-i;j<10+i+1;j++)12             a[i][j]=a[i-1][j-1]+a[i-1][j+1];13         for(i=0;i<10;i++)14         {15             for(j=0;j<21;j++)16                 if(a[i][j]==0)17                     printf("   ");18                 else{19                     if(a[i][j]<10)20                     {21                         printf("%2d",a[i][j]);22                     }23                     else if(a[i][j]<100)24                     {25                         printf("%2d",a[i][j]);26                     }27                     else{28                         printf("%d",a[i][j]);29                     }30                 }31                 printf("\n");32         }33                 printf("\n");34     return 0;35 }

运行结果: