字符串加空格

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int main()
{
    string s;
    getline (cin, s);
    for (int i = 0; i < s.size(); i ++ )
        cout << s[i] << " ";
}

字符串插入

#include<bits/stdc++.h>
using namespace std;
string st1,st2;
char x;
int i,p;
int main()
{
    while(cin>>st1>>st2){
        p=0;
        x=0;
        for(i=0;i<=st1.size()-1;i++)
            if(st1[i]>x){
                x=st1[i];
                p=i;
            }
        for(i=0;i<=p;i++)cout<<st1[i];
        cout<<st2;
        for(i=p+1;i<=st1.size()-1;i++)cout<<st1[i];
        cout<<endl;
    }
}

作者：垫底抽風
链接：https://www.acwing.com/solution/content/63316/
来源：AcWing
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只出现一次的字符

#include<iostream>
#include<cstdio>
#include<string>
using namespace std;
int main()
{
    string A;
    bool s=0;
    while(getline(cin,A))
    {
        for(int i=0;i<A.size();i++)
        {
            if(A.find(A[i])==A.rfind(A[i]))
            {
                cout<<A[i]<<endl;
                s=1;
                break;
            }
        }
    }
    if(s==0)
        cout<<"no"<<endl;
    return 0;
}

忽略大小写比较字符串大小

#include <iostream>
#include <cstring>
using namespace std;
int main()
{
    string s1, s2;
    getline(cin, s1);
    getline(cin, s2);
    for (int i = 0; s1[i]; i ++ ) if (s1[i] >= 'A' && s1[i] <= 'Z') s1[i] += 32;
    for (int i = 0; s2[i]; i ++ ) if (s2[i] >= 'A' && s2[i] <= 'Z') s2[i] += 32;
    for (int i = 0; s1[i] || s2[i]; i ++ )
    {
        if (s1[i] > s2[i]) 
        {
            puts(">");
            return 0;
        } else if (s1[i] < s2[i]) { 
            puts("<");
            return 0;
        }
    }
    puts("=");
    return 0;
}

去掉多余的空格

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int main(){
    string s;
    getline(cin,s);
    string ans;
    for(int i=0;s[i];i++){
        if(s[i]!=' '){
            ans+=s[i];
        }else{
            ans+=' ';
            int j=i;
            while(s[j] && s[j]==' '){
                j++;
            }
            i=j-1;
        }
    }
    cout<<ans<<endl;
    return 0;
}