算法初级_1：字符

main函数

• c++

#include <iostream>
using namespace std;

int main (int args, char* argv[])
{
    int c1 = 'a';
    int c2 = 'a'+3;

    cout<<"c1: \t"<<c1<<endl;
    cout<<"c2: \t"<<c1<<endl;

    return 0;
}

• c

#include "stdio.h"

int main (int args, char* argv[])
{
    int c1 = 'a';
    int c2 = 'a'+3;

    printf("%c - %d \n", c1, c1);
    printf("%c - %d \n", c2, c2);

    return 0;
}

字符串表达式

• sizeof

#include "stdio.h"
#include "string.h"

int main (int args, char* argv[])
{
    char str[]="JulyEdu";

    printf("%d \n", sizeof(str));
    printf("%d \n", strlen(str));

    return 0;
}

• 字符串的修改

#include "stdio.h"
#include "string.h"

int main (int args, char* argv[])
{
    char str[]="JulyEdu";

    str[4]='a';
    str[5]='p';
    str[6]='p';

    printf("%s \n",str);

    return 0;
}

//

#include "stdio.h"
#include "string.h"

int main (int args, char* argv[])
{
    char str[]="JulyEdu";

    *(str+4)='a';
    *(str+5)='p';
    *(str+6)='p';

    printf("%s \n",str);

    return 0;
}

//错误：因为“JulyEdu”是字符串常量，不可以修改

//标准写法
#include "stdio.h"
#include "string.h"

int main (int args, char* argv[])
{
    const char *str="JulyEdu";  //添加const标注

    printf("%s \n",str);

    return 0;
}

//指针修改常量字符串
#include<iostream>
#include <exception>
#include "string.h"

using namespace std;

#define FALSE -1

int main (int args, char* argv[])
{
    const char* strOrigin="JulyEdu";
    const int sizeNum=100;


    try{
    char *str=new char[sizeNum];
    strcpy(str,strOrigin);
    cout<<str<<endl;

    str[4]='a';
    str[5]='p';
    str[6]='p';
    cout<<str<<endl;
    delete []str;
    }catch (const bad_alloc& e){
        return -1;
    }

    return 0;
}

//c语言版的字符串修改
#include<iostream>
#include <exception>
#include "string.h"
#include<math.h>

using namespace std;

#define FALSE -1
#define ElemType char

int main (int args, char* argv[])
{
    const char* strOrigin="JulyEdu";
    const int sizeNum=100;

    char *str= (char*)malloc(sizeNum*sizeof(ElemType));
    if(!str) //分配存储失败
        exit(OVERFLOW);

    strcpy(str,"JulyEdu");
    str[4]='a';
    str[5]='p';
    str[6]='p';
    printf("%s\n",str);

    free(str);

    return 0;
}

凯撒加密

#include<iostream>
#include <exception>
#include<math.h>
#include<fstream>
using namespace std;

int main(int args, char* argv[])
{
    ifstream iFile("D://caesar.txt");
    if (!iFile.is_open()){              //文件打开错误
        cerr << "i_file open error!" << endl;
        exit(0);
    } 
    iFile.seekg(0,ios::end);    //读取文件的结尾
    int nFileLen=iFile.tellg(); //文件的长度
    iFile.seekg(0, ios::beg);

    try{
    char *str=new char[nFileLen+1];
    iFile.read(str, nFileLen);
    iFile.close();

    str[nFileLen]=0; //将数组最后一位设为0
    const int nCaesar=3;
    int n=0; //n记录回车的数量

    for(int i=0; i<nFileLen; i++){
        if((str[i]>='a') && (str[i]<='z')){
            str[i] += nCaesar;
            if(str[i] > 'z')
                str[i] -= 26;
        }
        else if((str[i] >= 'A') && (str[i]<='Z')){
            str[i] += nCaesar;
            if(str[i]>'Z')
                str[i] -= 26;
        }
        else if(str[i] == '\n'){
            n++;
        }
    }

    ofstream oFile("D://myCaesar.txt");
    oFile.write(str, nFileLen-n);
    oFile.close();

    delete[] str;
    return 0;

    }catch (const bad_alloc& e){
        return -1;
    }
}

异或加密

#include <stdio.h>
#include <stdlib.h>
#include<math.h>

int main(int args, char* argv[])
{
    FILE* pFile=fopen("D://caesar.txt");
    if(pFile==NULL){
        exit(0);
    }
    fseek(pFile,0,SEEK_END);
    char str*=(char*)malloc((nFileLen+1)*sizeof(char));
    if(!str)  //分配存储失败
        exit(OVERFLOW);
    fread(str,nFileLen,1,pFile);
    fclose(pFile);

    str[nFileLen]=0;
    const char*="JulyEdu";
    int nLen=(int)strlen(secreat);
    int j=0;

    for(int i=0;i<nFileLen;i++){
        str[i]^=secret[j];
        j++;
        if(j>=nLen)
            j-=nLen;
    }

    FILE *pFile2=fopen("D://mySong.txt","wb");
    fwrite(str,nFile,1,pFile2);
    fclose(pFile2);

    delete[] str;

}

删除空格

/*删除空格 1. main函数：输入字符；异常处理；调用函数；输出函数 2. 功能函数：removeBlank*/


#include <iostream>
using namespace std;

void removeBlank(char *pString)
{
    int j=0; 
    for(int i=0;pString[i]!='\0';i++){
        if(pString[i] != ' '){
            if(i!=j){
                pString[j]=pString[i];
            }
            j++;
        }
    }
    pString[j]=0;
}


int main(int args, char* argv[])
{
    char str[]= "I have a dream";
    removeBlank(str);
    cout<< str << endl;

    return 0;
}

• 指针版本

//dest：目标；ret：返回
#include <iostream>
#include <string.h>
using namespace std;

void removeBlank(char *pString)
{
    char *ret,*dest;  //双指针：ret=return；dest=目标
    for(ret=dest=pString;*ret!='\0';){
        if(*ret==' ')
            ret++;
        else 
            *dest++=*ret++;
    }
    *ret='\0';
}


int main(int args, char* argv[])
{
    char str[]= "I have a dream";
    removeBlank(str);
    cout<< str << endl;

    return 0;
}

• stl 版本

#include<iostream>
#include <string>
#include <algorithm>
using namespace std;



void main()
{
    string str("I have a dream");   //初始化
    string::iterator it = str.begin();
    while ((it=find(it, str.end(), ' '))!=str.end())
    {

            str.erase(it);
            if (it == str.end()) break;
        }  
    cout << str<<endl;
}

数组的最大数

#include<iostream>
using namespace std;

int Select(const int *a, int size);

int main(int args,char* argv[])
{
    const int a[]={1,3,5,2,5,32,15};
    int nMax=Select(a,sizeof(a)/sizeof(int));
    cout<< nMax <<endl;
}

int Select(const int* a, int size)
{
    int nMax=a[0];
    for(int i=1;i<size;i++){
        if(nMax < a[i])
            nMax=a[i];
    }

    return nMax;
}

数组中最大的两个数

#include<iostream>
using namespace std;

#defien ERROR 0;

void Select(const int* a, int size,int &nMax, int &nSecondMax);


int main(int args,char* argv[])
{
    const int a[]={1,3,5,2,5,32,15};
    int nMax, nSecondMax;
    Select(a,sizeof(a)/sizeof(int),nMax,nSecondMax);
    cout<< nMax <<endl;
    cout<< nSecondMax<<endl;
}

void Select(const int* a, int size,int &nMax, int &nSecondMax)
{
    nMax=a[0];
    nSecondMax=a[0];

    if(size==0)
       return ERROR;
    for(int i=1; i<size;i++){
        if(nMax<a[i]){
            nSecondMax=nMax;
            nMax=a[i];
        }
        else if (nSecondMax < a[i]){
            nSecondMax=a[i];
        }
    }
}