C语言 两个整数合并成一个整数

#include <stdio.h>long long mergeinteger1(int a, int b){long long sum = 0;//if (b >= 0)int mid = b;sum += a * 10;/*while (mid /= 10){sum *= 10;}*/for (;mid/=10;sum*=10);sum += b;return sum;}long long mergeinteger2(int a, int b){char A[100] = {0};long long res = 0;//A[19] = '\0';sprintf(A,"%d%d",a,b);//sscanf(A, "%d", &res);//printf("INFun:%lld\n",res);sscanf(A,"%lld",&res);//printf("A[]:%s\n",A);//printf("INT:%lld\n",res);return res;}int main(void){int a, b;scanf("%d %d", &a, &b);printf("%d%d\n", a, b);printf("merge:%lld\n", mergeinteger1(a, b));printf("merge:%lld\n", mergeinteger2(a, b));return 0;}