要面试了，写写小程序练练手，顺便记录一下

int i=0,j=0,tmp=0;
#define MAX_A 12
#define MAX_B 10

void main()
{
int i=0,j=0,tmp=0;
int a[MAX_A]={1,2,3,4,5,6,7,8,9,1,2,3};
int b[MAX_B]={1,2,1,2,1,2,1,2,1,2};
int c[MAX_A+MAX_B]={0};
for(i=0; i<MAX_A; i++){
for(j=0;j<MAX_B;j++){
tmp= b[MAX_B-j-1] * a[MAX_A-i-1] + c[MAX_A+MAX_B-1 -i-j]; /*current multiply*/
if(tmp>9)    c[MAX_A+MAX_B-1 -i-j-1] += tmp / 10;         /*high bit*/
c[MAX_A+MAX_B -1 -i -j] = tmp %10;                        /*low bit*/
}
}
for(i=0;i<MAX_A+MAX_B;i++)
printf("%d",c[i]);                /*output result*/
}

void main()
{
int total[256],max;
char  *p="abcdabcdaaaabcbbbbbbbbbbbdefg";
char *ps=p,max_char;
while(*ps!='\0'){
total[*ps]++;
if(total[*ps]>max){
max = total[*ps];
max_char = *ps;
}
ps++;
}
printf("max char=%c, number=%d\n",max_char,max);
}

void main()
{
char p[]="abcdefg";
int t=0,len=strlen(p);
while(1){
if(t==len/2) break;
p[t]^=p[len-1-t];
p[len-1 -t]^= p[t];
p[t] ^=p[len-1-t];
t++;
}
printf("reverse string=%s\n",p);
}

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
up_lower(char str[])
{
int i=0,len= strlen(str);
if(str[i]>='a'&&str[i]<='z')
str[i] = str[i]-'a'+'A';
i++;
while(i<len){
if(str[i]>='A'&&str[i]<='Z')
str[i] = str[i]+'a'-'A';
i++;
}
}
void main()
{
char a[]="aDSKLFJdfklsdjf";
up_lower(a);
printf("string=%s\n",a);
}

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
void swap(int *a,int *b)
{
int tmp=*a;
*a = *b;
*b = tmp;
}
void quick_once(int array[],int head,int tail)
{
int key,i,j,mid_pos;
key = array[head];
i = mid_pos = head;
j = tail;
if(head>=tail) return;
while(i<j){
while(array[j]>=key&&i<j)
j--;
if(i<j){
swap(array+j,array+mid_pos);
mid_pos=j;
}else break;
while(array[i]<=key&&i<j)
i++;
if(i<j){
swap(array+i,array+mid_pos);
mid_pos=i;
}else break;
}
quick_once(array,head,mid_pos-1);
quick_once(array,mid_pos+1,tail);
}
void main()
{
int i,a[]={1,2,3,4,5,6,7,8,9};
quick_once(a,0,sizeof(a)/sizeof(int)-1);
for(i=0;i<sizeof(a)/sizeof(int);i++) printf("%d ",a[i]);
}