c++语言字符串取模运算,C++ 大数运算（加减乘除取模）

加法：(字符串模拟小学加法)

string add(string s1, string s2) {

int len1 = s1.length(), len2 = s2.length();

int maxlen = max(len1, len2) + ;

string res(maxlen, '');

int flag = ;

int i = len1 - , j = len2 - , k = maxlen - ;

for (; i >= && j >= ; i--, j--) {

int temp = (s1[i] - '') + (s2[j] - '') + flag;

flag = temp / ;

res[k--]= temp % + '';

}

while (i >= ) {

int temp = s1[i--] - '' + flag;

flag = temp / ;

res[k--] = temp % + '';

}

while (j >= ) {

int temp = s2[j--] - '' + flag;

flag = temp / ;

res[k--] = temp % + '';

}

res[k] = flag