#include <stdio.h>
#include <math.h>
void solve(double a,double b,double c);
int main(){
    double a,b,c;
    printf("Enter a b c:");
    while(scanf("%lf%lf%lf",&a,&b,&c)!=EOF){
        solve(a,b,c);
        printf("Enter a b c:");
    }
    return 0;
}
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);
          x1=(-b-sqrt(delta))/(2*a);
          printf("x1=%f,x2=%f\n",real,imag);
      }
      else
 
{
          real=-b/(2*a);
          imag=sqrt(-delta)/(2*a);
          printf("x1=%f+%fi,x2=%f-%fi\n",real,imag,real,imag);
      }
    }
    
    
}

返回值只能有一個，不能多個返回，一元二次方程可能會返回兩個值

//利用區域性static變數計算階乘 
#include <stdio.h>
long long fac(int n);
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; 
}
long long fac(int n){
    static long long p=1;
    printf("p=%11d\n",p);
    p=p*n;
    return p;
}

//利用區域性static變數計算階乘 
#include <stdio.h>
long long fac(int n);
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; 
}
long long fac(int n){
    static long long p=1;
    p=p*n;
    return p;
}

#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);
}

首先a=k=4,b=m(主函式）=1,那麼i=2+1+0=3,m=3+4+1=8；p2:a=k=4,b=m(主函式)=1, static m為靜態變數，m=8,i=3+8+1=12,所以m=12+4+1=17

在修飾變數的時候，static 修飾的靜態區域性變數只執行初始化一次

//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==1) 
           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 = %lld\n", n, f);
    }
    
    return 0;
}
long long fun(int n){
    long long int f;
    if(n==1)
       f=1;
    else
        f=2*fun(n-1)+1;
    
    return f;
    
    

#include <stdio.h>
void draw(int n,char symbol);
#include <stdio.h>
int main(){
    int n,symbol;
    while(scanf("%d %c",&n,&symbol)!=EOF){
      draw(n,symbol);
      printf("\n");
    }
    return 0;
}
void draw(int n,char symbol){
    int i,k;
    for(k=1;k<=n;k++){
        for(i=1;i<=n-k;i++){
            printf(" ");
        }
        for(i=1;i<=2*k-1;i++){
            
            printf("%c",symbol);
        }
        printf("\n");
    }

}