Simplified C template for contest programming. There are two versions: #.c for problems without testcases and ##.c for problems with testcases. Additionally, there's a basic timer to get the execution time.

##.c

#include"stdio.h"
#include"string.h"
#include"math.h"
#include"stdlib.h"
#include"ctype.h"
#include"limits.h"
#include"time.h"
#include"stdbool.h"
#define ll long long

/*
int qualitysort(const void *a, const void *b)
{
	if(*(ll *)a > *(ll *)b)
	return 1;
	if(*(ll *)a < *(ll *)b)
	return -1;
	return 0;
}
*/

int main()			//for problems with testcases
{
	clock_t lnh=clock();
	int t,d=1;
	scanf("%d",&t);
	while(t--)
	{
	ll n,c=0,i,j;
	scanf("%lld",&n);
	
	//ll a[n];
	//for(i=0;i<n;scanf("%lld",&a[i++]));
	//qsort(a,n,sizeof(ll),qualitysort);
	//for(i=0;i<n;i++)
	printf("Case %d: ",d++);
	
	printf("%lld",c);
	printf("\n");
	}
	
	clock_t cls=clock();
	//printf("Execution Time: %fms\n",(double)((cls-lnh)*1000)/CLOCKS_PER_SEC);
	
	return 0;
}

#.c

#include"stdio.h"
#include"string.h"
#include"math.h"
#include"stdlib.h"
#include"ctype.h"
#include"limits.h"
#include"time.h"
#include"stdbool.h"
#define ll long long

/*
int qualitysort(const void *a, const void *b)
{
	if(*(ll *)a > *(ll *)b)
	return 1;
	if(*(ll *)a < *(ll *)b)
	return -1;
	return 0;
}
*/

int main()				//for problems free of testcases :)
{
	clock_t lnh=clock();
	ll n,c=0,i,j;
	scanf("%lld",&n);
	
	//ll a[n];
	//for(i=0;i<n;scanf("%lld",&a[i++]));
	//qsort(a,n,sizeof(ll),qualitysort);
	//for(i=0;i<n;i++)
	
	printf("%lld",c);
	printf("\n");
	
	clock_t cls=clock();
	//printf("Execution Time: %fms\n",(double)((cls-lnh)*1000)/CLOCKS_PER_SEC);
	
	return 0;
}