输入：scanf，注意scanf的指示符不加@

#import <Foundation/Foundation.h>
#import "MyFirstClass.h"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSLog(@"输入：");
        int c;
        scanf("%d", &c);
        NSLog(@"%d", c);
        return 0;
    }
    return 0;
}

输出：NSLog，可以不加修饰符。