C :

#include<stdio.h>
#include<string.h>
char c[255],b[255],a[255];
int max=-1;
int main()
{
	gets(c);
	int len=strlen(c);
	for(int i=0;i<len;i++)
	{
		if(c[i]!=' ')
		{
		int count=0;
		for(;i<len&&c[i]!=' ';i++)
		b[++count]=c[i];
		if(count>max)	
		{
		for(int j=1;j<=count;j++)
		a[j]=b[j];
		max=count;
		}
		}
	}
	for(int i=1;i<=max;i++)
	printf("%c",a[i]);
	return 0;
}

C++ :

#include <iostream>
#include <cstring>
using namespace std;

int main(){
	char s[1000];
	char w[1000];
	char m[1000] = "";
	gets(s);
	int i,k = 0;
	for (i = 0;i < strlen(s);i++){
		if (s[i] != ' '){
			w[k] = s[i];
			k++;
			if (i == strlen(s) - 1 || s[i + 1] == ' '){
				w[k] = '\0';
				//cout<<w<<endl;
				if (strlen(w) > strlen(m)){
					strcpy(m,w);
				}
				k = 0;
			}
		}
	}
	cout<<m;
}

Java :

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		String[] str=scanner.nextLine().split(" ");
		int maxLength=0;
		String maxStr=null;
		for(int i=0;i<str.length;i++){
			if(str[i].length()>maxLength){
				maxLength=str[i].length();
				maxStr=str[i];
			}
		}
		System.out.println(maxStr);
	}
}

Python :

str = input()
maxStr = "";   #存放长度最长的单词
k = 0          #存放最长单词的长度      
li = str.split(" ");
for i in range(0,len(li)):
    f = True
    for j in range(i + 1,len(li)):
        if len(li[i]) < len(li[j]):
            f = False;
            x = 1
            break;
    if f:
      print(li[i])
      break;