NSString *tempA = @"123";

  NSString *tempB = @"456";

1，字符串拼接

 NSString *newString = [NSString stringWithFormat:@"%@%@",tempA,tempB];

2，字符转int

int intString = [newString intValue];

3，int转字符

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

4，字符转float

 float floatString = [newString floatValue];

5，float转字符

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