NSString *newString =@“xxx”;
int intString = [newString intValue]; 

NSString *stringInt = [NSString stringWithFormat:@"%d",intString];  

float floatString = [newString floatValue]; 

NSString *stringFloat = [NSString stringWithFormat:@"%f",intString];  

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