第4章习题参考答案

《实用C语言简明教程》第4章习题参考答案4-1 B说明：B中y=x是赋值表达式，值是10，即非04-2 B说明：关键是要机会执行驶z++和w=2*z这两个表达式才能得到w=44-3条件表达式：#include "stdio.h"main(){float a,b;printf("enter a,b:");scanf("%f,%f",&a,&b);b>=0?printf("a+|b|=%f",a+b):printf("a+|b|=%f",a-b); }if语句：#include "stdio.h"main(){float a,b;printf("enter a,b:");scanf("%f,%f",&a,&b);if(b>=0)printf("a+|b|=%f",a+b);elseprintf("a+|b|=%f",a-b);}4-4#include "stdio.h"main(){int x;printf("enter a integer:"); scanf("%d",&x);if(x%3==00&&x%7==0) printf("%d:yes",x); elseprintf("%d:no",x);}4-5#include "stdio.h"main(){float x,fx;printf("enter a number:"); scanf("%f",&x);if(x>1)fx=x*x+1;elseif(x<-1)fx=x*x-1;elsefx=x*x;printf("fx=%f",fx);}4-6#include "stdio.h"main(){int a,b;a=b=5;if(a==3)if(b==5)printf("%d",a=a+b); elseprintf("%d",a=a-b); printf("%d",a);}运行结果：54-7#include "stdio.h"main(){int a;scanf("%d",&a);switch(a+1){case 3:a+=3;case 2:a+=2;break;case 4:default:a+=5;}printf("%d",a);}输入2时，输出：7输入3时，输出：84-8#include "stdio.h"main(){int age,y1,m1,d1,y2,m2,d2;printf("enter birthday(year month date):\n");scanf("%d%d%d",&y1,&m1,&d1);printf("enter current calendar(year month date):\n"); scanf("%d%d%d",&y2,&m2,&d2);age=y2-y1;if(m1>m2) age--;if(m1==m2&&d1>d2) age--;printf("age is %d\n",age);}4-9#include <stdio.h>#include <math.h>main(){float a,b,c;float delta,x1,x2;printf("please enter a:\n");scanf("%f",&a);printf("please enter b:\n");scanf("%f",&b);printf("please enter c:\n");scanf("%f",&c);delta=b*b-4.0*a*c;if(delta>0){x1=(-b+sqrt(delta))/(2.0*a);x2=(-b-sqrt(delta))/(2.0*a);printf("x1=%f,x2=%f\n",x1,x2);}elseif(delta==0){x1=x2=(-b)/(2.0*a);printf("x1=%f,x2=%f\n",x1,x2);}else{float m,n;m=sqrt(-delta)/(2.0*a);n=(-b)/(2.0*a);printf("x1=%f+%fi,x2=%f-%fi\n",n,m,n,m); }}4-10#include "stdio"main(){float money,sum;int term;printf("\nPlease enter savings money: "); scanf("%f",&money)printf("\nPlease enter savings term(month): "); scanf("%f",&term);switch(term){case 3:sum=money*(1+1.71/100);break;case 6:sum=money*(1+1.89/100);break;case 12:sum=money*(1+1.98/100);break;case 24:sum=money*(1+2.25/100);break;case 36:sum=money*(1+2.52/100);break;case 60:sum=money*(1+2.79/100);break;default:printf("error!");}printf("sum=%f\n",sum);}上机实习题1.if语句：#include "stdio.h"main(){float score;printf("please enter score:");scanf("%f",&score);if(score>=90&&score<=100)printf("score=%f,grade=EXCELLENT\n",score); else if(score>=70&&score<=89)printf("score=%f,grade=GOOD\n",score);else if(score>=60&&score<=69)printf("score=%f,grade=PASS\n",score);else if(score<60&&score>=0)printf("score=%f,grade=FAIL\n",score);elseprintf("error!");}switch语句：#include "stdio.h"main(){float score;int grad;printf("please enter score:");scanf("%f",&score);grad=(int)(score/10);switch(grad){case 10:case 9:printf("score=%5.2f,grade=EXCELLENT\n",score);break;case 8:case 7:printf("score=%5.2f,grade=GOOD\n",score);break;case 6:printf("score=%5.2f,grade=PASS\n",score);break;case 5:case 4:case 3:case 2:case 1:case 0:printf("score=%5.2f,grade=FAIL\n",score);break;default:printf("score=%f,error!",score);}}2.#include "stdio.h"main(){float a,b,r,t1,x1,y1,x2,y2;printf("please a,b:");scanf("%f,%f",&a,&b);printf("please r:");scanf("%f",&r);t1=4*(a*a*r*r+r*r-b*b);if(t1<0){printf("no solution!\n");}else if(t1==0){x1=-2*a*b/(2*(a*a+1));y1=a*x1+b;printf("x1=%f,y1=%f\n",x1,y1);}else{x1=(-2*a*b-t1)/(2*(a*a+1));y1=a*x1+b;x2=(-2*a*b+t1)/(2*(a*a+1));y2=a*x2+b;printf("x1=%f,y1=%f\nx2=%f,y2=%f\n",x1,y1,x2,y2); }}3.#include "stdio.h"main(){float x,y;printf("input x=");scanf("%f",&x);printf("x=%f\n",x);if((x>=-5.0&&x<0.0)&&(x!=-2)) y=1.0/(x+2);else if(x>=0.0&&x<5) y=1.0/(x+5);else if(x>=5.0&&x<10.0) y=1.0/(x+12);else y=0.0;printf("x=%e\ny=%e\n",x,y);}。