iOS 大数乘法运算

//大数乘法运算
+(NSString *)multiplyActionString:(NSString *)str1 andString:(NSString *)str2{

NSMutableArray *muArray = [[NSMutableArray alloc] init];

NSMutableString *string1 = [[NSMutableString alloc] initWithString:str1];
NSMutableString *string2 = [[NSMutableString alloc] initWithString:str2];

//第一步 取出两个乘数值后面相连的0 最后运算结果在补0
NSInteger i = 0;
while (i < str1.length) {
    
    NSString *number = [str1 substringWithRange:NSMakeRange(str1.length -1 -i, 1)];
    
    if (![number isEqualToString:@"0"]) {
        //不为0 跳出循环
        break;
    }
    
    //把取出的0添加到数组
    [muArray addObject:number];
    string1 = [str1 substringToIndex:str1.length -1-i].mutableCopy;
    
    i++;
}


NSInteger j = 0;
while (j < str2.length) {
    
    NSString *number = [str2 substringWithRange:NSMakeRange(str2.length -1 -j, 1)];
    
    if (![number isEqualToString:@"0"]) {
        //不为0则跳出循环
        break;
    }
    
    //把取出的0添加到数组
    [muArray addObject:number];