//一元二次方程求解 

//重複執行， 直到按下Ctrl+Z結束 
#include<stdio.h>
#include<math.h>

//函式宣告
void solve(double a, double b, double c);

//主函式
int main(){
    double a,b,c;
    
    printf("Enter a, b, c: ");
    while(scanf("%lf%lf%lf", &a, &b, &c) !=EOF){
        solve(a, b, c);//函式呼叫
        printf("
 
Enter a, b, c: "); 
    }
    
    return 0;
} 

//函式定義
//功能：求解一元二次方程，列印輸出結果
//形式引數：a,b,c為一元二次方程係數
void solve(double a, double b, double c){
    double x1,x2;
    double delta, real, imag;
    
    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);
        }
    }
}
 

不能，每次執行只能返回一個函式值，有兩個根。

//利用區域性static變數計算階乘

#include <stdio.h>
long long fac(int n);//函式宣告

int main(){
    int i,n;
    
    printf("Enter n: ");
    scanf(" %d", &n);
    
    for(i=1;i<=n; ++i)
        printf("%d！= %11d\n", i, fac(i));
        
    return 0;
} 

//函式定義
long long fac(int n){
    static long long p = 1;
    
    printf("p = %11d\n", p);
    p = p*n;
    
    return p;
} 

//練習：區域性static變數特性

#include<stdio.h>
int func(int,int);

int main(){
    int k=4,m=1,p1,p2;
    
    p1 = func(k,m) ;
    p2 = func(k,m) ;
    printf("%d,%d\n",p1,p2);
    
    return 0; 
} 

int func(int a,int b){
    static int m=0,i=2;
    
    i += m+1;
    m = i+a+b;
    
    return (m);
}

一致，8，17

儲存呼叫函式的值的改變

//尋找兩個整數之間的所有素數（包括這兩個整數），把結果儲存在陣列bb中，函式返回素數的個數。
//例如，輸入6和21，則輸出為:7 11 13 17 19。

#include<stdio.h>

#define N 1000
int fun(int n,int m,int bb[N]){
    int i,j,k=0,flag;
    
    for(j=n;j<=m;j++){
            flag=1;
        for(i=2;i<j;i++)
            if(j%i==0){
            flag=0;
            break;
        }
        if(flag!=0 ) 
            bb[k++]=j;
    }
    return k;
}

int main(){
    int n=0,m=0,i,k,bb[N];
    
    scanf("%d",&n);
    scanf("%d",&m);
    
    for(i=0;i<m-n;i++)
        bb[i]=0;
        
    k=fun(n,m,bb);
    
    for(i=0;i<k;i++)
        printf("%4d",bb[i]);
        
        return 0;
}

#include<stdio.h>
long long fun(int n);

int main(){
    int n;
    long long f;
    
    while(scanf("%d",&n)!=EOF){
        f = fun(n);
        printf("n = %d,f = %11d\n",n,f);
    }
    
    return 0;
}
long long fun(int n){
    long long a;
    if(n==0)
        a=0;
    else
        a=2*fun(n-1)+1;
    return a;
}  

//一元二次方程求解 

//重複執行， 直到按下Ctrl+Z結束 
#include<stdio.h>
#include<math.h>

//函式宣告
void solve(double a, double b, double c);

//主函式
int main(){
    double a,b,c;
    
    printf("Enter a, b, c: ");
    while(scanf("%lf%lf%lf", &a, &b, &c) !=EOF){
        solve(a, b, c);//函式呼叫
        printf("Enter a, b, c: "); 
    }
    
    return 0;
} 

//函式定義
//功能：求解一元二次方程，列印輸出結果
//形式引數：a,b,c為一元二次方程係數
void solve(double a, double b, double c){
    double x1,x2;
    double delta, real, imag;
    
    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);
        }
    }
}

不對