用C语言编写要求如下程序

1。求一元二次方程的根，用循环语句实现可重复输入系数a,b,c的值 2，统计全班学生成绩，输入一学生的两课分数，计算输出每个学生的总分和平均分，此外如果平均分大于等于85为优秀，60-85为通过，统计成绩优秀和及格的学生

#include <stdio.h>
#include <math.h>

int main()
{
double a, b, c, d;
double x1, x2;
printf( "Input (a b c)three numbers：\n" );
printf( "No number out:\n" );
while ( scanf( "%lf%lf%lf", &a, &b, &c ) ) {
d = b*b - 4*a*c;
if ( d >= 0 ) {
x1 = ( -b + sqrt( d ) ) / (2*a);
x2 = ( -b - sqrt( d ) ) / (2*a);
printf( "x1=%.3f\tx2=%.3f\n", x1, x2 );
} else {
printf( "error\n");
}
}
}

英语表达不好，将就下

#include<stdio.h>

int main() { float x, y; float sum; float avg;

while(scanf("%f%f", &x, &y) != EOF) { sum = x + y; avg = sum /2;

printf("总分：%f\n", sum); printf("平均分：%f\n", avg); if(avg >= 85) { printf("优秀\n"); } else if(avg >= 60 && avg < 85) { printf("通过\n"); } else { printf("不及格\n"); } }

return 0; }

第一题： #include <stdio.h> #include <math.h> int main() { double a, b, c, d; double x1, x2; printf( "请输入一元二次方程的三个系数(a b c)\n" ); printf( "输入非数字字符退出程序：\n" ); while ( scanf( "%lf%lf%lf", &a, &b, &c ) ) { d = b*b - 4*a*c; if ( d >= 0 ) { x1 = ( -b + sqrt( d ) ) / (2*a); x2 = ( -b - sqrt( d ) ) / (2*a); printf( "x1=%.3f\tx2=%.3f\n", x1, x2 ); } else { x1 = -b / (2*a); x2 = sqrt( -d ) / (2*a); printf( "x1=%.2f+%.3fi\tx2=%.2f-%.3fi\n", x1, x2, x1, x2 ); } } } 运行截图： 第二题： #include <stdio.h> #include <math.h> double a[100][2]; int main() { int i, n, good = 0, pass = 0; double s1, s2; printf( "请输入你要输入的记录数量：" ); scanf( "%d", &n ); for ( i = 0; i < n; ++i ) { printf( "请输入第 %d 个学成的两科成绩：", i+1 ); scanf( "%lf%lf", &s1, &s2 ); a[i][0] = s1 + s2; a[i][1] = a[i][0] / 2; if ( a[i][1] >= 85 ) ++good; else if ( 60 <= a[i][1] && a[i][1] < 85 ) ++pass; } printf( "\n\n\t\t总分\t\t平均分\n\n" ); for ( i = 0; i < n; ++i ) { printf( "学生%d：\t\t%.2f\t\t%.2f\n", i+1, a[i][0], a[i][1] ); } printf( "\n优秀者：%d 人\n", good ); printf( "及格者：%d 人\n\n", pass ); } 运行截图：

#include<stdio.h> typedef struct student { float score[2]; float avg; }stu; main() { stu *p; int i,j=0,x=0,y=0,z=0; char a; for( i=1 ; ; i++ ) { printf("请输入学生两门课成绩：\n"); scanf("%f%f",&p->score[0],&p->score[1]); p->avg=(p->score[0]+p->score[1])/2; if(p->avg>=85) { printf("\n\t该生优秀!\n"); x++; }else if(p->avg>=60&&p->avg<85) { printf("\n\t通过!\n"); y++; }else { printf("\n\t该生不及格!\n"); z++; } printf("是否继续录入学生信息<y/n>:"); fflush(stdin); //清空缓冲内存区 scanf("%c",&a); fflush(stdin); if(a=='n') break; } printf("一共录入%d人信息\n优秀%d人\n通过%d人\n不及格%d人\n\n",i,x,y,z); }

1)当a等于0时退出：

#include <stdio.h> #include <stdlib.h> #include <math.h>

int main() { float a,b,c,i,root1,root2; printf("请输入三个系数：（输入格式：a,b,c)\n"); scanf("%f,%f,%f",&a,&b,&c); getchar(); while(a!=0) { i=b*b-4*a*c; if(i>0) { root1=(-b+sqrt(i))/(2*a); root2=(-b-sqrt(i))/(2*a); printf("方程有两不等实根：\n"); printf("%f,%f\n",root1,root2); } else if(i==0) { root1=root2=-b/(2*a); printf("方程有两相等实根：\n"); printf("%f,%f\n",root1,root2); } else { root1=(-b)/(2*a); root2=sqrt(-i)/(2*a); printf("方程有两复根：\n"); printf("%f+%fi,%f-%fi\n",root1,root2,root1,root2); } printf("请输入三个系数：（输入格式：a,b,c)\n"); scanf("%f,%f,%f",&a,&b,&c); getchar(); } return 0; } 结果：