求助qaq

#include<bits/stdc++.h>
int p,q,l,num=0,tmp=1,sum;
char c[16];
int main() {
	scanf("%d%s%d",&p,c,&q);
	l=strlen(c);
	for(int i=l-1; i>=0; i--) {
		if(c[i]<='9'&&c[i]>='0')num=c[i]-'0';
		else num=c[i]-'A'+10;
		sum+=tmp*num;
		tmp*=p;
	}
	l=0;
	while(sum) {
		tmp=sum%q;
		sum/=q;
		if(tmp>=0&&tmp<=9)c[l++]=tmp+'0';
		else c[l++]=tmp-10+'A';
	}
	for(int i=l-1; i>=0; i--)printf("%c",c[i]);
	return 0;
}