# Experiment 4

2020-12-06 21:31:44

```//  Solving quadratic equation of one variable  （ Function implementation mode ）
//  repeat ,  Until you press Ctrl+Z end

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

//  Function declaration
void solve(double a, double b, double c);

//  The main function
int main() {
double a, b, c;

printf("Enter a, b, c: ");
while(scanf("%lf%lf%lf", &a, &b, &c) != EOF) {
solve(a, b, c);  //  Function call
printf("Enter a, b, c: ");
}

return 0;
}

//  Function definition
//  function ： Solving a quadratic equation of one variable , printout
//  Formal parameters ：a,b,c Is the coefficient of quadratic equation of one variable
void solve(double a, double b, double c) {
double x1, x2;
double delta, real, imag;

if(a == 0)
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);
}
}
}```

Can not be , Because there are two roots of a quadratic equation of one variable .

```//  Using parts static Variable computes factorials

#include <stdio.h>
long long fac(int n);  //  Function declaration

int main() {
int i,n;

printf("Enter n: ");
scanf("%d", &n);

for(i=1; i<=n; ++i)
printf("%d! = %lld\n", i, fac(i));

return 0;
}

//  Function definition
long long fac(int n) {
static long long p = 1;
printf("p = %lld\n", p);
p = p*n;

return p;
}```

Local static The characteristic of a variable is to repeat the last number , And talk about the corresponding operations .

```//  practice ： Local static Variable characteristics

#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);
}```

After program running , The initial value of the second operation is the final value at the end of the first operation .

```// Find all primes between two integers ( Including these two integers ), Save the results in an array bb in , Function returns the number of primes .
//  for example , Input 6 and 21, The output of :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 = 4;
for(i=2;i<j;i++)
if(j % i == 0) {
flag=0;
break;
}
if(flag == 4)
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);   //  Function declaration

int main() {
int n;
long long f;

while(scanf("%d", &n) != EOF) {
f = fun(n);  //  Function call
printf("n = %d, f = %lld\n", n, f);
}

return 0;
}

//  Function definition
//  Make up ...
long long fun(int n) {
long long int s = 2;
if(n == 1)
s = s - 1;
else if(n >= 2 && n <=32)
s = s*(fun(n-1)+1)-1;

return s;
}```

```#include <stdio.h>

void draw(int n, char symbol);  //  Function declaration

#include <stdio.h>
int main() {
int n, symbol;

while(scanf("%d %c", &n, &symbol) != EOF) {
draw(n, symbol);  //  Function call

printf("\n");
}

return 0;
}

//  Function definition
//  Complement code ...
void draw(int n, char symbol) {
int i, a;
for(i = 1;i <= n; ++i) {
for(a = n-i;a > 0;a--)
printf(" ");
for(a = 2*i-1;a > 0;a--)
printf("%c", symbol);
printf("\n");
}
}```

https://chowdera.com/2020/12/20201206213051715b.html