NSString *str2=@"999";
NSString *str3=@"888";
int num=[str2 intValue ];
int num1=[str3 intValue];
int num3=num+num1;
NSString*STRNUM=[[NSString alloc]initWithFormat:@"%d",STRNUM ];
NSLog(@"%@",STRNUM);
原文：http://www.cnblogs.com/xzz5211314/p/5118043.html