Project Euler Problem 13 [closed]

Question

Hi.

I'm a novice C programmer. I'm trying to solve problem 13 but I feel as if my solution isn't as elegant as it could be. Can you please help me by providing me with advice on how to solve this problem using the C programming language? Thank you.

Problem:

Find the first ten digits of the sum of one-hundred 50-digit numbers.

This is my code:

#include<stdio.h>

int main()

{

   char tab[100] = { 37107287533902102798797998220837590246510135740250,
                     46376937677490009712648124896970078050417018260538,
                     74324986199524741059474233309513058123726617309629,
                     91942213363574161572522430563301811072406154908250,
                     23067588207539346171171980310421047513778063246676,
                     89261670696623633820136378418383684178734361726757,
                     28112879812849979408065481931592621691275889832738,
                     44274228917432520321923589422876796487670272189318,
                     47451445736001306439091167216856844588711603153276,
                     70386486105843025439939619828917593665686757934951,
                     62176457141856560629502157223196586755079324193331,
                     64906352462741904929101432445813822663347944758178,
                     92575867718337217661963751590579239728245598838407,
                     58203565325359399008402633568948830189458628227828,
                     80181199384826282014278194139940567587151170094390,
                     35398664372827112653829987240784473053190104293586,
                     86515506006295864861532075273371959191420517255829,
                     71693888707715466499115593487603532921714970056938,
                     54370070576826684624621495650076471787294438377604,
                     53282654108756828443191190634694037855217779295145,
                     36123272525000296071075082563815656710885258350721,
                     45876576172410976447339110607218265236877223636045,
                     17423706905851860660448207621209813287860733969412,
                     81142660418086830619328460811191061556940512689692,
                     51934325451728388641918047049293215058642563049483,
                     62467221648435076201727918039944693004732956340691,
                     15732444386908125794514089057706229429197107928209,
                     55037687525678773091862540744969844508330393682126,
                     18336384825330154686196124348767681297534375946515,
                     80386287592878490201521685554828717201219257766954,
                     78182833757993103614740356856449095527097864797581,
                     16726320100436897842553539920931837441497806860984,
                     48403098129077791799088218795327364475675590848030,
                     87086987551392711854517078544161852424320693150332,
                     59959406895756536782107074926966537676326235447210,
                     69793950679652694742597709739166693763042633987085,
                     41052684708299085211399427365734116182760315001271,
                     65378607361501080857009149939512557028198746004375,
                     35829035317434717326932123578154982629742552737307,
                     94953759765105305946966067683156574377167401875275,
                     88902802571733229619176668713819931811048770190271,
                     25267680276078003013678680992525463401061632866526,
                     36270218540497705585629946580636237993140746255962,
                     24074486908231174977792365466257246923322810917141,
                     91430288197103288597806669760892938638285025333403,
                     34413065578016127815921815005561868836468420090470,
                     23053081172816430487623791969842487255036638784583,
                     11487696932154902810424020138335124462181441773470,
                     63783299490636259666498587618221225225512486764533,
                     67720186971698544312419572409913959008952310058822,
                     95548255300263520781532296796249481641953868218774,
                     76085327132285723110424803456124867697064507995236,
                     37774242535411291684276865538926205024910326572967,
                     23701913275725675285653248258265463092207058596522,
                     29798860272258331913126375147341994889534765745501,
                     18495701454879288984856827726077713721403798879715,
                     38298203783031473527721580348144513491373226651381,
                     34829543829199918180278916522431027392251122869539,
                     40957953066405232632538044100059654939159879593635,
                     29746152185502371307642255121183693803580388584903,
                     41698116222072977186158236678424689157993532961922,
                     62467957194401269043877107275048102390895523597457,
                     23189706772547915061505504953922979530901129967519,
                     86188088225875314529584099251203829009407770775672,
                     11306739708304724483816533873502340845647058077308,
                     82959174767140363198008187129011875491310547126581,
                     97623331044818386269515456334926366572897563400500,
                     42846280183517070527831839425882145521227251250327,
                     55121603546981200581762165212827652751691296897789,
                     32238195734329339946437501907836945765883352399886,
                     75506164965184775180738168837861091527357929701337,
                     62177842752192623401942399639168044983993173312731,
                     32924185707147349566916674687634660915035914677504,
                     99518671430235219628894890102423325116913619626622,
                     73267460800591547471830798392868535206946944540724,
                     76841822524674417161514036427982273348055556214818,
                     97142617910342598647204516893989422179826088076852,
                     87783646182799346313767754307809363333018982642090,
                     10848802521674670883215120185883543223812876952786,
                     71329612474782464538636993009049310363619763878039,
                     62184073572399794223406235393808339651327408011116,
                     66627891981488087797941876876144230030984490851411,
                     60661826293682836764744779239180335110989069790714,
                     85786944089552990653640447425576083659976645795096,
                     66024396409905389607120198219976047599490197230297,
                     64913982680032973156037120041377903785566085089252,
                     16730939319872750275468906903707539413042652315011,
                     94809377245048795150954100921645863754710598436791,
                     78639167021187492431995700641917969777599028300699,
                     15368713711936614952811305876380278410754449733078,
                     40789923115535562561142322423255033685442488917353,
                     44889911501440648020369068063960672322193204149535,
                     41503128880339536053299340368006977710650566631954,
                     81234880673210146739058568557934581403627822703280,
                     82616570773948327592232845941706525094512325230608,
                     22918802058777319719839450180888072429661980811197,
                     77158542502016545090413245809786882778948721859617,
                     72107838435069186155435662884062257473692284509516,
                     20849603980134001723930671666823555245252804609722,
                     53503534226472524250874054075591789781264330331690 };

int s=0, i;

for(i=0; i<100; i++)

s+=tab[i];

printf("\n %s\n", tab[i]);

}

Answer 1

You want to know how to get started with Project Euler problem 13 in the C programming language.

A practical option is to obtain and become acquainted with the relevant part of a suitable free, open-source library. I would suggest as your first choice http://gmplib.org and if you want an alternative, you can find more here:

• http://en.wikipedia.org/wiki/Arbitrary-precision_arithmetic#Libraries
• http://stackoverflow.com/questions/1047203/best-bignum-library-to-solve-project-euler-problems-in-c

Another possibility is to spend some time considering how you might use mathematical insight to determine the first ten digits of that sum.

The programming language provides operations on numbers up to a limited size. It is commonly true, but certainly not universally true, that a C unsigned int can represent more than 40% of the ten-digit numbers. Your platform's limit for a C unsigned int is available to you as the macro UINT_MAX when you #include <limits.h>.

So, can you somehow divide this problem and conquer it?

For me, much of the attraction of Project Euler is in spending perhaps several days casting for approaches to a problem. If I preferred not to find the solution techniques by guess and by golly, I would be studying my old textbook on number theory instead. (And actually, I started doing exactly that, but not before I solved 76 problems without it.)