for，while，if语句的作用范围只再下一个分号，看书时仔细点就好。

# include <stdio.h>
 
int main(void)
 {
     int i;
     int sum = 0;

     for (i=1; i<=12; ++i)
     {
         sum = sum +i;
         printf("AAAAAAAAAAAAAAAAAA\n");
     }
    return 0;
 }

循环了阿，sum=78，只不过不是你要的循环吧。

悲剧..............

# include <stdio.h>

int main(void)
{
    int i;
    int sum = 0;

    for (i=1; i<=12; ++i)
     {  
    sum = sum +i;
    printf("AAAAAAAAAAAAAAAAAA\n");
     }
    return 0;
}