NSString*
string; // 结果字符串
NSString* string1, string2; //已存在的字符串
1. string = [NSString initWithFormat:@"%@,%@", string1, string2 ];
2. string = [string1 stringByAppendingString:string2];
3 . string = [string stringByAppendingFormat:@"%@,%@",string1, string2];