C :

#include<stdio.h>
#include<string.h>
char a[20],b[20];
int main(){
	scanf("%s%s",&a,&b);
	int ah = (a[0]-'0')*10+a[1]-'0';
	int am = (a[3]-'0')*10+a[4]-'0';
	int as = (a[6]-'0')*10+a[7]-'0';
	
	int bh = (b[0]-'0')*10+b[1]-'0';
	int bm = (b[3]-'0')*10+b[4]-'0';
	int bs = (b[6]-'0')*10+b[7]-'0';
	
	int at=ah*3600+am*60+as;
	int bt=bh*3600+bm*60+bs;
	
	printf("%d",at-bt);
	return 0;
}

C++ :

#include <iostream>
#include <cstring>
using namespace std;
int main(){
	char s[1000];
	gets(s);
	int h1,m1,t1;
	 h1=(s[0]-48) * 10 + (s[1]-48) * 1;
	 m1=(s[3]-48) * 10 + (s[4]-48) * 1;
	 t1=(s[6]-48) * 10 + (s[7]-48) * 1;
	 
	 
	 char v[1000];
	 gets(v);
	 int h2,m2,t2;
	 h2=(v[0]-48) * 10 + (v[1]-48) * 1;
	 m2=(v[3]-48) * 10 + (v[4]-48) * 1;
	 t2=(v[6]-48) * 10 + (v[7]-48) * 1;
	 int c;
	 c=0;
	 c=(h1-h2)*3600+(m1-m2)*60+(t1-t2);
	 cout<<c<<endl;
	 }

Java :

import java.util.Scanner;
public class Main{
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		String str=scanner.nextLine();
		String[] timeArray=str.split(":");
		int xh=Integer.valueOf(timeArray[0]);
		int fz=Integer.valueOf(timeArray[1]);
		int ms=Integer.valueOf(timeArray[2]);
		int all=xh*3600+fz*60+ms;
		String str1=scanner.nextLine();
		String[] timeArray1=str1.split(":");
		int xh1=Integer.valueOf(timeArray1[0]);
		int fz1=Integer.valueOf(timeArray1[1]);
		int ms1=Integer.valueOf(timeArray1[2]);
		int all1=xh1*3600+fz1*60+ms1;
		System.out.println(all-all1);
	}
}

Python :

a = input()
b = input()
x = a.split(':')
y = b.split(':')
c = int(x[0]) * 3600 + int(x[1]) * 60 + int(x[2]) -  int(y[0])*3600 - int(y[1])*60 - int(y[2])
print(c)