从C出发 11 --- 数组

 

 

 

 数组元素: 通过数组创建的变量

 

 

int n = 0;
int flag =0;
int i = 0;
int sum =0;

do
{
    printf("Input : ");

    scanf("%d", &n);

    flag = ((0 <= n) && (n <= 100));

    if(flag)
    {
            sum=0;
            for(i=0;i<=n;i++)
            {        
                sum += i;
            }

             printf("Sum = %d\n", sum);
    }
    while(flag);

   
}

提高效率, 因为上面的程序每次都要重新计算

int n = 0;
int flag =0;
int i = 0;

int sum [101];

for(n=0; n<=100; n++)
{
    sum[n] = 0;

    for(i=0; i<=n ;i++)
    {
        sum[n] += i;
    }
}

do
{
    printf("Input : ");

    scanf("%d", &n);

    flag = ((0 <= n) && (n <= 100));

    if(flag)
    {
           

             printf("Sum = %d\n", sum[n]);
    }
    while(flag);

   
}

继续改进，做递推

int n = 0;
int flag =0;

int sum [101];

sum[0] = 0;

for(n=1; n<=100; n++)
{
    
    sum[n] = sum[n-1] + n;    //sum[1] = sum[0] + 1;
                              //sum[2] = sum[1] + 2;
                              //......
}

do
{
    printf("Input : ");

    scanf("%d", &n);

    flag = ((0 <= n) && (n <= 100));

    if(flag)
    {
           

             printf("Sum = %d\n", sum[n]);
    }
    while(flag);

   
}