#include <math.h>
#include <stdio.h>
#include <stdlib.h>
int main() {
float a, b, c, x1, x2;
float delta, real, imag;
printf("Enter a, b, c: ");
while(scanf("%f%f%f", &a, &b, &c)) {
if(a == 0)
printf("not quadratic equation.\n");
else {
delta = b*b - 4*a*c;
if(delta >= 0) {
x1 = (-b + sqrt(delta)) / (2*a);
x2 = (-b - sqrt(delta)) / (2*a);
printf("x1 = %f, x2 = %f\n", x1, x2);
}
else {
real = -b/(2*a);
imag = sqrt(-delta) / (2*a);
printf("x1 = %f + %fi, x2 = %f - %fi\n", real, imag, real, imag);
}
}
printf("Enter a, b, c:\n");
}
system("pause");
return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main() {
int guessNumber;
int ans; // 存放用户猜的数字
srand((time(0))); // 以时间函数作为随机种子
guessNumber = 1 + rand()%100; // 生成1~100之间的随机数
do {
printf("your guess number is(1~100): ");
scanf("%d", &ans);
if(ans < guessNumber)
printf("%d is lower than the number.\n", ans);
else if(ans > guessNumber)
printf("%d higher then the number.\n", ans);
}while(ans != guessNumber);
printf("Congratulations. you hit it~\n");
system("pause"); // 在devc中运行时，这一行可以去掉
return 0;
}

#include <stdio.h>
#include <stdlib.h>
int main() {
int number, max, min, n;
n=1;
printf("输入第%d个数: ", n);
scanf("%d", &number);
max = number;
min = number;
while(/*补足①*/) {
n++;
printf("输入第%d个数: ", n);
scanf("%d", &number);
if(/*补足②*/)
max = number;
else if(/*补足③*/)
min = number;
}
printf("最大数为: %d\n", max);
printf("最小数为: %d\n", min);
system("pause");
return 0;
}

#include<stdio.h>
int isprime(int n);
int main()
{
int i,j;
j=0;
for(i=101;i<=200;i++)
{
if(isprime(i))
printf("%4d",i);
if(i%25==0)
printf("\n");
} 
for(i=101;i<=200;i++)
{
if(isprime(i))
j=j+1;
}
printf("\n101~200之间共有%d个素数",j);
getchar();
return 0;
}
int isprime(int n)
{
int k;
for(k=2;k<=n/2;k++)
if(n%k==0)
return 0;
return 1;
}

#include<stdio.h>
int main(){
long sr;
int a,b,c,d,e,f,g,h;
printf("请输入一个八位数");
scanf("%ld",&sr);
a=int(sr/10000000);
if(a%2==1)
    printf("a");
b=int(sr-10000000*a);
if(b%2==1)
    printf("b");
c=int(sr-10000000*a-1000000*b);
if(c%2==1)
    printf("c");
d=int(sr-10000000*a-1000000*b-100000*c);
if(d%2==1)
    printf("d");
e=int(sr-10000000*a-1000000*b-100000*c-10000*d);
if(e%2==1)
    printf("e");
f=int(sr-10000000*a-1000000*b-100000*c-10000*d-1000*e);
if(f%2==1)
    printf("f");
g=int(sr-10000000*a-1000000*b-100000*c-10000*d-1000*e-100*f);
if(g%2==1)
    printf("g");
h=int(sr-10000000*a-1000000*b-100000*c-10000*d-1000*e-100*f-10*g);
if(h%2==1)
    printf("h");
getchar();
    return 0;
}

不知道咋做。。。