hdu 1047 (big integer sum, fgets or scanf, make you func return useful infos)

errors made,

boundary conditions, <= vs < ,

decreasing vs increasing , ++, –,

‘0’/’1’ vs 0/1

prototype of sum, return the starting position of c-style string containing the sum, just like sprintf return number of characters successfully read.

[code]p1=sum(p1,p2);

and

[code]p=sprintf(p,"%09d",x);

have some similarities.

[code]#include <cstdio>
#include <cstring>

char* sum(char *to, char *from) {
    static const int charzero='0',oublecharzero='0'+'0';
    int sz1=strlen(to), sz2=strlen(from), nszmax,nszmin, i,j, tmp,carry;
    if(sz1>=sz2) { nszmax=-sz2, nszmin=-sz1; }
    else { nszmax=-sz1, nszmin=-sz2; }
    to+=sz1, from+=sz2;
    for(carry=0,i=-1;i>=nszmax;--i) {
        tmp=carry+to[i]+from[i]-doublecharzero;
        to[i]=charzero+tmp%10; carry=tmp/10;
    }
    if(sz2>sz1) {
        for(j=i;j>=nszmin;--j) to[j]=from[j];
        sz1=sz2;
    }
    if(carry) {
        for(j=i;j>=nszmin && to[j]=='9';--j) to[j]='0';
        if(j<nszmin) { to[j]='1'; ++sz1; }
        else { ++to[j]; }
    }
    return to-sz1;
}

int main() {
    //freopen("input.txt","r",stdin);
    const int MAXSIZE=101;
    int ncase,i,j;
    char buf1[MAXSIZE+2]={0}, buf2[MAXSIZE+2]={0}, *p1,*p2;
    scanf("%d",&ncase);
    for(i=1;i<=ncase;++i) {
        p1=buf1+MAXSIZE, p2=buf2; p1[0]='0', p1[1]=0;
        while(scanf("%100s",p2)==1 && strcmp(p2,"0")!=0) {
            p1=sum(p1,p2);
        }
        puts(p1); if(i!=ncase) putchar('\n');
    }
    return 0;
}