int i, max, min;
int a[5];

(a[5]への整数の格納は省略)

max = min = a[0];
for(i = 1; i < 5; i++) {
　if (max < a[i]) max = a[i];
　if (min > a[i]) min = a[i];
}

printf("最大値 %d\n最小値 %d\n", max, min);