Factorial 1-100

/***************************************
   factorial of huge nos
   correction: huge factorials of nos less than 100.
     Shaha Hassan
     Jan19, 2014
   Note: delete the lines commented "conio" if you are on a compiler which does not support conio(any modern compiler)
******************************************/
#include<stdio.h>
#include<conio.h>
#define MXP 170
#define MXN 6

void s2i(char *c, int *n);
void i2s(int *n, char *c);
void show(int *n);
void get(int *n);
void mul(int *n1, int *n2, int *product);
int isZero(int *n);
void copy(int *dst, int *src);
void dec(int *n);

void main()
{
    int n[MXN], tmp[MXP], pro[MXP];

    clrscr();       //conio
    printf("\nEnter number: ");
    get(n);
    pro[0] =pro[1] = 1;
    while( !isZero(n) ) {
    copy(tmp, pro);
    mul(tmp,n,pro);
    dec(n);
    }

    printf("FActorial is  ");
    show(pro);
    getch();        //conio
}

void dec(int *n) {
    int i=1;
    if( n[1] != 0 ) {  //non zero unit place
    if( (--n[1]==0) && (n[0]==1) ) {
        n[0] = 0;
    }
    }else{             //no ends in 0s
    i=1;
    while( n[i] ==0 ) {
        n[i++] = 9;
    }
    n[i]--;
    //sync size or n[0]
    if(n[n[0]] == 0) {
        n[0]--;
    }
    }
}

void copy(int *d, int *s) {
    int i;
    for(i=0; i<=s[0]; i++) {
    d[i]= s[i];
    }
}

int isZero(int *n) {
    return !(n[0]);
}

void mul(int *v, int *r, int *p) {
    int i,j, k;
    for(i=0; i<MXP; p[i++]=0);

    for(i=1; i<=r[0]; i++) {
    for(j=1; j<=v[0]; j++) {
        p[i+j-1] += v[j] * r[i];
        if( p[i+j-1] > 9) {
        p[i+j] += p[i+j-1] /10;
        p[i+j-1] %= 10;
        }
    }
    }
    k = v[0]+r[0]+1;
    while( p[k--]==0);
    p[0]=k+1;
}

void get(int *n)
{
    char buf[MXN];
    scanf("%s",buf);
    if(strlen(buf)> MXN) {
    printf("too big. Try again");
    get(n);
    return;
    } else {
    strrev(buf);
    s2i(buf,n);
    }
}

void show(int *n)
{
    char buf[MXP];
    i2s(n,buf);
    strrev(buf);
    printf("%s = %d.%de+%d",buf,n[n[0]], n[n[0]-1], n[0]-1);
}

void s2i(char *c, int *n)
{
    int i;
    n[0] = strlen(c);
    for(i=0; i<n[0]; i++) {
    n[i+1] = c[i] - '0';
    }
}

void i2s(int *n, char *c)
{
    int i;
    for(i=1; i<=n[0]; i++) {
    c[i-1] = n[i] +'0';
    }
    c[i-1] = '\0';
}
//end