排序的地方小改一下即可

# include <stdio.h>
int main() 
{
    float a[4];
	int i;
	int j;
	float k;
	float Ave = 0;
	char b[4][2];
	char l;
	
	for(i = 0; i < 4; i = i + 1)	
		scanf("%s %f", &b[i], &a[i]);
	for(i = 0; i < 4; i = i + 1)
		for(j = 0; j < (4 - i) - 1; j = j + 1)
		{
			if(a[j] > a[j + 1])
			{
				k = a[j];
				a[j] = a[j + 1];
				a[j + 1] = k;
				
				// l = b[j][2];
				// b[j][2] = b[j + 1][2];
				// b[j + 1][2] = l;
				l = b[j][0];
				b[j][0] = b[j + 1][0];
				b[j + 1][0] = l;
				l = b[j][1];
				b[j][1] = b[j + 1][1];
				b[j + 1][1] = l;
			
			}	
		}
	for(i = 0; i < 4; i = i + 1)
		Ave = Ave + a[i];
	Ave = Ave / 4;
	
	printf("Max = %.2f %s\n", a[3], b[3]);
	printf("min = %.2f %s\n", a[0], b[0]);
	printf("Ave = %.2f\n", Ave);
	
}

首先不知道你為什麼要宣告為char b[4][2]，看起來沒有用到，所以我擅自把它拿掉改為char b[4]，所以回圈內的那個[2]也可以拿掉了，另外要提醒的是printf("Max = %.2f %s\n", a[3], b[3]);內的%s是給一個字串，但b[3]是字元，所以應該改為%c，若引用錯誤很可能造成Access violation reading location 0x00000066.

改完如下

# include <stdio.h>
main()
{
	float a[4];
	int i;
	int j;
	float k;
	float Ave = 0;
	char b[4];
	char l;


	for (i = 0; i < 4; i = i + 1)
		scanf("%s %f", &b[i], &a[i]);
	for (i = 0; i < 4; i = i + 1)
		for (j = 0; j < (4 - i) - 1; j = j + 1)
		{
			if (a[j] > a[j + 1])
			{
				k = a[j];
				a[j] = a[j + 1];
				a[j + 1] = k;

				l = b[j];
				b[j] = b[j + 1];
				b[j + 1] = l;


			}
		}
	for (i = 0; i < 4; i = i + 1)
		Ave = Ave + a[i];
	Ave = Ave / 4;

	printf("Max = %.2f %c\n", a[3], b[3]);
	printf("min = %.2f %c\n", a[0], b[0]);
	printf("Ave = %.2f\n", Ave);

}

輸出

k 85
v -5
f 89
d 10
Max = 89.00 f
min = -5.00 v
Ave = 44.75

新增1-以字串處理方式

# include <stdio.h>
main()
{
	float a[4];
	int i;
	int j;
	float k;
	float Ave = 0;
	char b[4][2];
	char l;


	for (i = 0; i < 4; i = i + 1)
		scanf("%s %f", &b[i][0], &a[i]);  // 名字存到b[i][0]，'\0'會存到b[i][1]
	for (i = 0; i < 4; i = i + 1)
		for (j = 0; j < (4 - i) - 1; j = j + 1)
		{
			if (a[j] > a[j + 1])
			{
				k = a[j];
				a[j] = a[j + 1];
				a[j + 1] = k;
                
                // b[j][1]都是'\0'
                // 只需換名字就好 因此只須換b[j][0]與b[j+1][0]
				l = b[j][0];
				b[j][0] = b[j + 1][0];
				b[j + 1][0] = l;


			}
		}
	for (i = 0; i < 4; i = i + 1)
		Ave = Ave + a[i];
	Ave = Ave / 4;

	printf("Max = %.2f %s\n", a[3], &b[3][0]);  // %s要給字串的指標 所以用&
	printf("min = %.2f %s\n", a[0], &b[0][0]);  // %s要給字串的指標 所以用&
	printf("Ave = %.2f\n", Ave);

}

l = b[j][2];
b[j][2] = b[j + 1][2];
b[j + 1][2] = l;

這蠻有趣的,
宣告b[4][2]應該只會有b[j][0]跟b[j][1]而已吧,
所以b[j][2]是跑到下一個記憶體位置了?
變成b[j+1][0]的位置??

可以將成績讀進來就直接處理:

for (i = 0; i < 4; i = i + 1)
{
scanf("%s %f", &b[i], &a[i]);
SUM=SUM+a[i];
if(a[i]>MAX)
MAX=i;
if(a[i]<MIN)
MIN=i;
}