For some reason whenever I input a number above 12 it = 0.
Here is my code (I've tried using a long int but that just comes up with random numbers instead):
#include <stdio.h>
int main()
{
{
int c, n, f = 1;
printf("Enter a number to calculate its factorial\n");
scanf("%d", &n);
for (c = 1; c <= n; c )
f = f * c;
if (n < 0)
printf("Cannot calculate the factorial of a negative number\n");
else
{
printf("Factorial of %d = %d\n", n, f);
}
}
CodePudding user response：
#include <stdio.h>
int main()
{
unsigned long long c, n, f = 1;
printf("Enter a number to calculate its factorial\n");
scanf("%llu", &n);
for (c = 1; c <= n; c )
f = f * c;
if (n < 0)
printf("Cannot calculate the factorial of a negative number\n");
else
{
printf("Factorial of %llu = %llu\n", n, f);
}
}
CodePudding user response：
Factorials get very large very fast - N! will overflow the native integer types for relatively low values of N.
To calculate any factorial larger than 20!, you will need to use a multi-precision library like GNU MP, like so:
#include <stdio.h>
#include <gmp.h>
#include <assert.h>
unsigned long fac( unsigned long n )
{
unsigned long ret = 1;
while( n )
ret *= n--;
return ret;
}
int main( void )
{
for ( unsigned long i = 0; i < 21; i )
{
/**
* Calculate factorial with native unsigned long type
*/
printf( "fac(%2lu) = !lu\t", i, fac(i) );
/**
* Calculate factorial using GMP - note that 99! has
* 157 digits - that's roughly equivalent to 518 bits.
* The largest native integer types currently max out
* at 64 bits.
*/
mpz_t rop;
mpz_fac_ui( rop, i );
gmp_printf( "mpz_fac_ui(-) = 7Zd\n", i, rop );
}
printf( "------------ limit of unsigned long --------------\n" );
for ( unsigned long i = 21; i < 100; i )
{
printf( "fac(%2lu) = !lu\t", i, fac(i) );
mpz_t rop;
mpz_fac_ui( rop, i );
gmp_printf( "mpz_fac_ui(-) = 7Zd\n", i, rop );
}
return 0;
}
Output of the program is:
fac( 0) = 1 mpz_fac_ui( 0) = 1
fac( 1) = 1 mpz_fac_ui( 1) = 1
fac( 2) = 2 mpz_fac_ui( 2) = 2
fac( 3) = 6 mpz_fac_ui( 3) = 6
fac( 4) = 24 mpz_fac_ui( 4) = 24
fac( 5) = 120 mpz_fac_ui( 5) = 120
fac( 6) = 720 mpz_fac_ui( 6) = 720
fac( 7) = 5040 mpz_fac_ui( 7) = 5040
fac( 8) = 40320 mpz_fac_ui( 8) = 40320
fac( 9) = 362880 mpz_fac_ui( 9) = 362880
fac(10) = 3628800 mpz_fac_ui(10) = 3628800
fac(11) = 39916800 mpz_fac_ui(11) = 39916800
fac(12) = 479001600 mpz_fac_ui(12) = 479001600
fac(13) = 6227020800 mpz_fac_ui(13) = 6227020800
fac(14) = 87178291200 mpz_fac_ui(14) = 87178291200
fac(15) = 1307674368000 mpz_fac_ui(15) = 1307674368000
fac(16) = 20922789888000 mpz_fac_ui(16) = 20922789888000
fac(17) = 355687428096000 mpz_fac_ui(17) = 355687428096000
fac(18) = 6402373705728000 mpz_fac_ui(18) = 6402373705728000
fac(19) = 121645100408832000 mpz_fac_ui(19) = 121645100408832000
fac(20) = 2432902008176640000 mpz_fac_ui(20) = 2432902008176640000
------------ limit of unsigned long --------------
fac(21) = 14197454024290336768 mpz_fac_ui(21) = 51090942171709440000
fac(22) = 17196083355034583040 mpz_fac_ui(22) = 1124000727777607680000
fac(23) = 8128291617894825984 mpz_fac_ui(23) = 25852016738884976640000
fac(24) = 10611558092380307456 mpz_fac_ui(24) = 620448401733239439360000
fac(25) = 7034535277573963776 mpz_fac_ui(25) = 15511210043330985984000000
fac(26) = 16877220553537093632 mpz_fac_ui(26) = 403291461126605635584000000
fac(27) = 12963097176472289280 mpz_fac_ui(27) = 10888869450418352160768000000
fac(28) = 12478583540742619136 mpz_fac_ui(28) = 304888344611713860501504000000
fac(29) = 11390785281054474240 mpz_fac_ui(29) = 8841761993739701954543616000000
fac(30) = 9682165104862298112 mpz_fac_ui(30) = 265252859812191058636308480000000
fac(31) = 4999213071378415616 mpz_fac_ui(31) = 8222838654177922817725562880000000
fac(32) = 12400865694432886784 mpz_fac_ui(32) = 263130836933693530167218012160000000
fac(33) = 3400198294675128320 mpz_fac_ui(33) = 8683317618811886495518194401280000000
fac(34) = 4926277576697053184 mpz_fac_ui(34) = 295232799039604140847618609643520000000
fac(35) = 6399018521010896896 mpz_fac_ui(35) = 10333147966386144929666651337523200000000
fac(36) = 9003737871877668864 mpz_fac_ui(36) = 371993326789901217467999448150835200000000
fac(37) = 1096907932701818880 mpz_fac_ui(37) = 13763753091226345046315979581580902400000000
fac(38) = 4789013295250014208 mpz_fac_ui(38) = 523022617466601111760007224100074291200000000
fac(39) = 2304077777655037952 mpz_fac_ui(39) = 20397882081197443358640281739902897356800000000
fac(40) = 18376134811363311616 mpz_fac_ui(40) = 815915283247897734345611269596115894272000000000
fac(41) = 15551764317513711616 mpz_fac_ui(41) = 33452526613163807108170062053440751665152000000000
fac(42) = 7538058755741581312 mpz_fac_ui(42) = 1405006117752879898543142606244511569936384000000000
fac(43) = 10541877243825618944 mpz_fac_ui(43) = 60415263063373835637355132068513997507264512000000000
fac(44) = 2673996885588443136 mpz_fac_ui(44) = 2658271574788448768043625811014615890319638528000000000
fac(45) = 9649395409222631424 mpz_fac_ui(45) = 119622220865480194561963161495657715064383733760000000000
fac(46) = 1150331055211806720 mpz_fac_ui(46) = 5502622159812088949850305428800254892961651752960000000000
fac(47) = 17172071447535812608 mpz_fac_ui(47) = 258623241511168180642964355153611979969197632389120000000000
fac(48) = 12602690238498734080 mpz_fac_ui(48) = 12413915592536072670862289047373375038521486354677760000000000
fac(49) = 8789267254022766592 mpz_fac_ui(49) = 608281864034267560872252163321295376887552831379210240000000000
fac(50) = 15188249005818642432 mpz_fac_ui(50) = 30414093201713378043612608166064768844377641568960512000000000000
fac(51) = 18284192274659147776 mpz_fac_ui(51) = 1551118753287382280224243016469303211063259720016986112000000000000
fac(52) = 9994050523088551936 mpz_fac_ui(52) = 80658175170943878571660636856403766975289505440883277824000000000000
fac(53) = 13175843659825807360 mpz_fac_ui(53) = 4274883284060025564298013753389399649690343788366813724672000000000000
fac(54) = 10519282829630636032 mpz_fac_ui(54) = 230843697339241380472092742683027581083278564571807941132288000000000000
fac(55) = 6711489344688881664 mpz_fac_ui(55) = 12696403353658275925965100847566516959580321051449436762275840000000000000
fac(56) = 6908521828386340864 mpz_fac_ui(56) = 710998587804863451854045647463724949736497978881168458687447040000000000000
fac(57) = 6404118670120845312 mpz_fac_ui(57) = 40526919504877216755680601905432322134980384796226602145184481280000000000000
fac(58) = 2504001392817995776 mpz_fac_ui(58) = 2350561331282878571829474910515074683828862318181142924420699914240000000000000
fac(59) = 162129586585337856 mpz_fac_ui(59) = 138683118545689835737939019720389406345902876772687432540821294940160000000000000
fac(60) = 9727775195120271360 mpz_fac_ui(60) = 8320987112741390144276341183223364380754172606361245952449277696409600000000000000
fac(61) = 3098476543630901248 mpz_fac_ui(61) = 507580213877224798800856812176625227226004528988036003099405939480985600000000000000
fac(62) = 7638104968020361216 mpz_fac_ui(62) = 31469973260387937525653122354950764088012280797258232192163168247821107200000000000000
fac(63) = 1585267068834414592 mpz_fac_ui(63) = 1982608315404440064116146708361898137544773690227268628106279599612729753600000000000000
fac(64) = 9223372036854775808 mpz_fac_ui(64) = 126886932185884164103433389335161480802865516174545192198801894375214704230400000000000000
fac(65) = 9223372036854775808 mpz_fac_ui(65) = 8247650592082470666723170306785496252186258551345437492922123134388955774976000000000000000
fac(66) = 0 mpz_fac_ui(66) = 544344939077443064003729240247842752644293064388798874532860126869671081148416000000000000000
fac(67) = 0 mpz_fac_ui(67) = 36471110918188685288249859096605464427167635314049524593701628500267962436943872000000000000000
fac(68) = 0 mpz_fac_ui(68) = 2480035542436830599600990418569171581047399201355367672371710738018221445712183296000000000000000
fac(69) = 0 mpz_fac_ui(69) = 171122452428141311372468338881272839092270544893520369393648040923257279754140647424000000000000000
fac(70) = 0 mpz_fac_ui(70) = 11978571669969891796072783721689098736458938142546425857555362864628009582789845319680000000000000000
fac(71) = 0 mpz_fac_ui(71) = 850478588567862317521167644239926010288584608120796235886430763388588680378079017697280000000000000000
fac(72) = 0 mpz_fac_ui(72) = 61234458376886086861524070385274672740778091784697328983823014963978384987221689274204160000000000000000
fac(73) = 0 mpz_fac_ui(73) = 4470115461512684340891257138125051110076800700282905015819080092370422104067183317016903680000000000000000
fac(74) = 0 mpz_fac_ui(74) = 330788544151938641225953028221253782145683251820934971170611926835411235700971565459250872320000000000000000
fac(75) = 0 mpz_fac_ui(75) = 24809140811395398091946477116594033660926243886570122837795894512655842677572867409443815424000000000000000000
fac(76) = 0 mpz_fac_ui(76) = 1885494701666050254987932260861146558230394535379329335672487982961844043495537923117729972224000000000000000000
fac(77) = 0 mpz_fac_ui(77) = 145183092028285869634070784086308284983740379224208358846781574688061991349156420080065207861248000000000000000000
fac(78) = 0 mpz_fac_ui(78) = 11324281178206297831457521158732046228731749579488251990048962825668835325234200766245086213177344000000000000000000
fac(79) = 0 mpz_fac_ui(79) = 894618213078297528685144171539831652069808216779571907213868063227837990693501860533361810841010176000000000000000000
fac(80) = 0 mpz_fac_ui(80) = 71569457046263802294811533723186532165584657342365752577109445058227039255480148842668944867280814080000000000000000000
fac(81) = 0 mpz_fac_ui(81) = 5797126020747367985879734231578109105412357244731625958745865049716390179693892056256184534249745940480000000000000000000
fac(82) = 0 mpz_fac_ui(82) = 475364333701284174842138206989404946643813294067993328617160934076743994734899148613007131808479167119360000000000000000000
fac(83) = 0 mpz_fac_ui(83) = 39455239697206586511897471180120610571436503407643446275224357528369751562996629334879591940103770870906880000000000000000000
fac(84) = 0 mpz_fac_ui(84) = 3314240134565353266999387579130131288000666286242049487118846032383059131291716864129885722968716753156177920000000000000000000
fac(85) = 0 mpz_fac_ui(85) = 281710411438055027694947944226061159480056634330574206405101912752560026159795933451040286452340924018275123200000000000000000000
fac(86) = 0 mpz_fac_ui(86) = 24227095383672732381765523203441259715284870552429381750838764496720162249742450276789464634901319465571660595200000000000000000000
fac(87) = 0 mpz_fac_ui(87) = 2107757298379527717213600518699389595229783738061356212322972511214654115727593174080683423236414793504734471782400000000000000000000
fac(88) = 0 mpz_fac_ui(88) = 185482642257398439114796845645546284380220968949399346684421580986889562184028199319100141244804501828416633516851200000000000000000000
fac(89) = 0 mpz_fac_ui(89) = 16507955160908461081216919262453619309839666236496541854913520707833171034378509739399912570787600662729080382999756800000000000000000000
fac(90) = 0 mpz_fac_ui(90) = 1485715964481761497309522733620825737885569961284688766942216863704985393094065876545992131370884059645617234469978112000000000000000000000
fac(91) = 0 mpz_fac_ui(91) = 135200152767840296255166568759495142147586866476906677791741734597153670771559994765685283954750449427751168336768008192000000000000000000000
fac(92) = 0 mpz_fac_ui(92) = 12438414054641307255475324325873553077577991715875414356840239582938137710983519518443046123837041347353107486982656753664000000000000000000000
fac(93) = 0 mpz_fac_ui(93) = 1156772507081641574759205162306240436214753229576413535186142281213246807121467315215203289516844845303838996289387078090752000000000000000000000
fac(94) = 0 mpz_fac_ui(94) = 108736615665674308027365285256786601004186803580182872307497374434045199869417927630229109214583415458560865651202385340530688000000000000000000000
fac(95) = 0 mpz_fac_ui(95) = 10329978488239059262599702099394727095397746340117372869212250571234293987594703124871765375385424468563282236864226607350415360000000000000000000000
fac(96) = 0 mpz_fac_ui(96) = 991677934870949689209571401541893801158183648651267795444376054838492222809091499987689476037000748982075094738965754305639874560000000000000000000000
fac(97) = 0 mpz_fac_ui(97) = 96192759682482119853328425949563698712343813919172976158104477319333745612481875498805879175589072651261284189679678167647067832320000000000000000000000
fac(98) = 0 mpz_fac_ui(98) = 9426890448883247745626185743057242473809693764078951663494238777294707070023223798882976159207729119823605850588608460429412647567360000000000000000000000
fac(99) = 0 mpz_fac_ui(99) = 933262154439441526816992388562667004907159682643816214685929638952175999932299156089414639761565182862536979208272237582511852109168640000000000000000000000
CodePudding user response：
For some reason whenever I input a number above 12 it = 0.
The reason is the largest value a 32-bit signed integer can hold is 231-1 or 2,147,483,647. 13! is 6,227,020,800, so you have exceeded the bounds of a C int.
If your compiler supports it, unsigned long long will get you to 20!:
unsigned long long(64-bits) max is 264-1 or 18,446,744,073,709,551,615- 20! = 2,432,902,008,176,640,000 (ok)
- 21! = 51,090,942,171,709,440,000 (too big)
You need a "big integer" library to handle integers bigger than this.
Or, use Python