打印2~100的素數(shù)：
int main(int argc,char *argv[])
{ int num,i,j;
int arr[50];
int index = 1;
for(num = 2;num < 100;num++)
{
for(j = 2;j <= num;j++)
{
if(num % j == 0)
break;
}
if(j == num)
{
arr[index] = num; index++; }
}
for(i = 0;i < index;i++)
{
if(i % 5 == 0 && i / 5 != 0)
printf("\n"); printf("%4d",arr[i]); }
return 0;
}

在已排好序的數(shù)組中插入一個數(shù)，人讓其排好輸出：

include<stdio.h>

int main()
{
int arr[6] = {4,6,33,35,65};
int i,insert,temp;
printf("input a num of insert:\n");
scanf("%d",&insert); //insert = 5;
for(i = 0;i < 6;i++)
{
if(arr[i]>insert)
{
temp = arr[i];
arr[i] = insert; insert = temp;
}
}
arr[5] = insert;
for(i = 0;i<6;i++)
{
printf("%d ",arr[i]);
}
printf("\n");
return 0;
}

課堂筆記：
指針：
野指針：沒有初始化，或者其指向的內(nèi)存被釋放，而指針沒有被置空；危害：造成段錯誤處，出現(xiàn)未知的錯誤。
指針的運算：指針的自增和自減自增：指針向高地址方向移動；自減：指針向低地址方向移動；指針不能相加，只能相減；
概念區(qū)分int buf[3];int *pb;int arr[3];指針數(shù)組int (pa)[3];數(shù)組指針
二級指針：DataType **pointername;int a = 10;int *p = &a;int pa = &p;pa = *p = a = 10;

總結(jié)：今天講的東西重在理解數(shù)組，理解數(shù)組和指針之間的各項，要學(xué)會思路的理轉(zhuǎn)換和理解作業(yè):

1.編程輸入一行文字，找出其中的大寫字母，小寫字母，空格，數(shù)字，及其他字符的個數(shù)（用指針實現(xiàn)）#include<stdio.h>
int main(int argc,char argv[])
{
char arr[100];
char p = arr;
int index = 0;
int capital_count = 0;
int lowercase_count = 0;
int space_count = 0;
int number_count = 0;
int other_count = 0;
printf("input string:");
for(p = arr;p < arr+100;p++)
{
scanf("%c",p);
if(p == '\n')
break;
//index++;
else if(p>='A' && *p<='Z') capital_count ++;

                         else if(*p>='a' && *p<='z') lowercase_count ++;
                         else if(*p == 32) space_count ++; 
                        else if(*p>=48 && *p<=57) number_count ++; 
                        else other_count ++; 
                    } 
                         printf("大寫字母：%4d\n小寫字母：%4d\n空格：%4d\n數(shù)字：%4d\n其他：  %4d\n",capital_count,lowercase_count,space_count,number_count,other_count);    
                      printf("%d",index); return 0;}

2.從鍵盤輸入5個整數(shù)存入一個數(shù)組。然后輸入另外一個數(shù)，用指針的方法從中查找該數(shù)是否存在，如果找到，輸出該數(shù)所在的下標(biāo)，否則輸出消息："沒有找到"。
//在數(shù)組中查找一個數(shù)然后輸出下標(biāo)#include<stdio.h>
int main(int argc,char *argv[])
{
int index = 0;
int arr[5];
int pointer = arr;
int i = 0;
printf("input five number:");
for(i = 0;i < 5;i++)
scanf("%d",pointer+i);
int seek_num = 0;
printf("input a num of seeking:");
scanf("%d",&seek_num);
for(pointer = arr;pointer < arr + 5;pointer++)
{
if(pointer == seek_num){ i = pointer -arr; index++;
printf("this number is found!index is :%d\n",i);
}
}
if(index == 0)
printf("Dont found!!!\n");
return 0;
}

3.char a[5]="hello"; char b[5]="world"; char c[14];用指針方法將數(shù)組a和數(shù)組b的內(nèi)容存到數(shù)組c中//合并字符串

include<stdio.h>

int main(int argc,char *argv[])
{
char a[5] = "hello";
char b[5] = "world";
char c[14] = {0};
char *pa = a;
char *pb = b;
char *pc = c;
for(pa = a;pa < a+5;pa++,pc++) *pc = *pa;
for(pb = b;pb < b+5;pb++,pc++) *pc = *pb; pc = c;
printf("%s\n",pc);
}