【原】C语言学习——指针精华（1）

C语言精华-指针01

指针变量的引用
代码入下：

//通过指针变量访问整型变量
#include <stdio.h>

int main(void)
{
int  a, b, *p1, *p2;
a = 100; b = 10;
p1 = &a; p2 = &b;
printf("a=%d, b=%d\n", a, b);
printf("*p1=%d, *p2=%d\n", *p1, *p2);
printf("&a=%x, &b=%x\n", &a, &b);
printf("p1=%x, p2=%x\n", p1, p2);
printf("&p1=%x, &p2=%x\n", &p1, &p2);

return 0;
}

结果为：

指针变量作为函数参数—地址传递：
【工程案例】将数从大到小输出：

#include <stdio.h>
void swap(int  x, int y)  
{
int  temp;
temp = x;
x = y;
y = temp;
}
int main(void)
{
int a, b;
scanf_s("%d,%d", &a, &b);
if (a<b)  swap(a, b);
printf("\na=%d,b=%d\n", a, b);
return 0;
}

值传递！！！！！！！！！！！！！！！！！！！！！！！！








【工程案例】将数组a中n个整数按相反顺序存放。
方法一：

//⑴ 实参与形参均用数组
#include <stdio.h>
void inv(int  x[], int n);
int main()
{
int i, a[10] = { 3, 7, 9, 11, 0, 6, 7, 5, 4, 2 };
printf("The original array:\n");
for (i = 0; i<10; i++)   
printf("%4d",a[i]);
printf("\n");
inv(a, 10);
printf("The array has been inverted:\n");
for (i = 0; i<10; i++)   
printf("%4d", a[i]);
printf("\n");
return 0；
}

void inv(int  x[], int n)
{
int temp, i, j, m = (n - 1) / 2;
for (i = 0; i <= m; i++){
j = n - 1 - i;
temp = x[i];  x[i] = x[j];  x[j] = temp;
}
return;
}

结果为：

方法二：

//⑵ 实参用数组，形参用指针变量
#include <stdio.h>
void inv(int  *x, int n);
int main()
{
int i, a[10] = { 3, 7, 9, 11, 0, 6, 7, 5, 4, 2 };
printf("The original array:\n");
for (i = 0; i<10; i++)   printf("%4d",a[i]);
printf("\n");
inv(a, 10);
printf("The array has been inverted:\n");
for (i = 0; i<10; i++)   printf("%4d",a[i]);
printf("\n");
return 0;
}
void inv(int  *x, int n)
{
int temp, *p, *i, *j, m = (n - 1) / 2;
i = x;  j = x + n - 1;  p = x + m;
for (; i <= p; i++, j--){
temp = *i;  *i = *j;  *j = temp;
}
return;
}

结果为：

方法三：

//(3)实参与形参均用指针变量
#include <stdio.h>
int main()
{
void inv(int *x, int n);
int i, arr[10], *p = arr;
printf("The original array:\n");
for (i = 0; i<10; i++, p++)
scanf_s("%d", p);
p = arr;  inv(p, 10);
printf("The array has been inverted:\n");
for (p = arr; p<arr + 10; p++)
printf("%4d", *p);
printf("\n");
return 0;
}

void inv(int *x, int n)
{
int *p, m, temp, *i, *j;
m = (n - 1) / 2;
i = x;  j = x + n - 1;  p = x + m;
for (; i <= p; i++, j--)
{
temp = *i; *i = *j; *j = temp;
}
}

结果为：

方法四：

//⑷ 实参用指针变量，形参用数组
#include <stdio.h>
int main()
{
void inv(int  x[], int n);
int i, a[10], *p = a;
for (i = 0; i<10; i++, p++)
scanf_s("%d", p);
p = a;
inv(p, 10);
printf("The array has been inverted:\n");
for (p = a; p<a + 10; p++)
printf("%4d", *p);
printf("\n");
return 0;
}

void inv(int  x[], int n)
{
int t, i, j, m = (n - 1) / 2;
for (i = 0; i <= m; i++)
{
j = n - 1 - i;
t = x[i];  x[i] = x[j];  x[j] = t;
}
}

结果同上。

【工程案例】3个学生各学4门课，计算总平均分，输出第n个学生成绩

#include <stdio.h>

void average(float  *p, int  n);
void search(float(*p)[4], int  n);

int main()
{
float score[3][4] =
{ { 65, 67, 79, 60 }, { 80, 87, 90, 81 },
{ 90, 99, 100, 98 } };
average(*score, 12);
search(score, 2);
return 0;
}
void average(float *p, int n)
{
float  *p_end, sum = 0, aver;
p_end = p + n - 1;
for (; p <= p_end; p++)
sum = sum + (*p);
aver = sum / n;
printf("average=%5.2f\n", aver);
}
void search(float(*p)[4], int n)
{
int i;
printf("score of  No.%d  :\n", n);
for (i = 0; i < 4; i++)
printf("%5.2f  ", *(*(p + n) + i));
printf("\n");
}

结果可以自行测试。

总结：二维数组与一维数组指针变量的关系