OC方法-- NSString截取,比较,拼接，判断，强转

NSString:

1.subStringToIndex:1  截取字符串,(截取到1)

  NSString *str = @"我是一串字符串";
    NSString *strJieQu = [str substringToIndex:1];
    NSLog(@"截取str:%@", strJieQu);

 运行结果：截取str:我

2.subStringFromIndex:1 截取字符串（从1开始截取）

NSString *str = @"我是一串字符串";
    NSString *strJieQu = [str substringFromIndex:1];
    NSLog(@"截取str:%@", strJieQu);

运行结果：截取str：是一串字符串

3. stringWithFormat:(NSString) 字符串的万能初始化方法

 NSString *str = @"我是一串字符串";
    NSInteger num = 5;
    CGFloat floatNum = 3.14;
    NSString *strJieQu = [NSString stringWithFormat:@"%@, %ld, %f", str, num, floatNum];
    NSLog(@"截取str:%@", strJieQu);

运行结果：我是一串字符串, 5, 3.140000

4.stringByReplaceOccurrencesOfString:(NSString) withString:(NSString)字符串的替换

    NSString *str = @"我是一串字符串";
    NSString *strJieQu = [str stringByReplacingOccurrencesOfString:@"我" withString:@"你"];
    NSLog(@"截取str:%@", strJieQu);

运行结果：截取str:你是一串字符串

5.stringByAppendingFormat:(NSString) 字符串的拼接

    NSString *str = @"我是一串字符串";
    NSString *strJieQu = [str stringByAppendingFormat:@"%@, 我很happy", str];
    NSLog(@"截取str:%@", strJieQu);

运行结果：截取str:我是一串字符串我是一串字符串, 我很happy

6. 判断字符串是否相等:
     isEqual:
     isEqualToString:(NSString);

   常用于if条件判断

NSString *str = @"我是一串字符串";
    NSString *strJieQu = [str stringByAppendingFormat:@"%@, 我很happy", str];
    if ([str isEqualToString:@"我是一串字符串"]) {
        
        NSLog(@"一样");
    }
    else
    {
        NSLog(@"截取str:%@", strJieQu);
    }

运行结果：一样

7. compare : 字符串比较

    NSString *str = @"我是一串字符串";
    NSLog(@"截取str:%ld", (long)[str compare:@"178"]);

运行结果：1

8. hasPrefix: 判断字符串开头是否相等

    NSString *str = @"我是一串字符串";
    if ([str hasPrefix:@"我"]) {
        
        NSLog(@"YES");
    }
    else
    {
        NSLog(@"NO");
    }

运行结果：YES

9. hasSuffix: 判断字符串结尾是否相等

    NSString *str = @"我是一串字符串";
    if ([str hasSuffix:@"我"]) {
        
        NSLog(@"YES");
    }
    else
    {
        NSLog(@"NO");
    }

运行结果：NO 10. intValue   :强转成整型
11.integerValue :强转成NSInteger型

12 floatValue:强转CGFloat型