#include<stdio.h>
struct stu
{
    int num;
    char *name;
    char sex;
    float score;
}
boy[5]={
    {101,"Li ping","M",45},
    {102,"Zhang ping","M"62.5},
    {103,"He fang ","F",92.5},
    {104,"Cheng ling","F",87},
    {105,"Wang ming","M",58},
};
main()
{
    int i,c=0;
    float ave,s=0;
    for(i=0;i<5;i++)
    {
        s+=boy[i].score;
        if(boy[i].score<60) c+=1;

    }
    printf("s=%f\n",s);
        ave=s/5;
    printf("average=%f\ncount=%d\n",ave,c);
}

"M" 等改为 'M'
"M"62.5 之间也少了个逗号吧

一针见血我sex前面加个*可以吗

你是指 *sex 还是 *"M"; 前者错误，后者虽然怪异但可以

另外，你应该规规矩矩写代码

#include <stdio.h>

struct stu
{
    int num;
    char name[50];
    char sex;
    float score;
};

int main( void )
{
    struct stu boy[5] = { {101, "Li ping",    'M', 45.0f }
                        , {102, "Zhang ping", 'M', 62.5f }
                        , {103, "He fang",    'F', 92.5f }
                        , {104, "Cheng ling", 'F', 87.0f }
                        , {105, "Wang ming",  'M', 58.0f } };

    float sum = 0;
    unsigned failures = 0;
    const size_t count = sizeof(boy)/sizeof(*boy);
    for( size_t i=0; i!=count; ++i )
    {
        sum += boy[i].score;
        if( boy[i].score < 60 )
            ++failures;
    }

    printf( "sum = %.1f\n", sum );
    printf( "average = %.2f\n", sum/count );
    printf( "Number of failures = %u\n", failures );
}

刚刚起步啥都不懂