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;}

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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 -1int 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 charint 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;}

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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;}

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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;}

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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;}

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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];        }    }}