小编mat*_*mpp的帖子

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

int main(void) 
{ 
    double x = 4.0, result; 

    result = sqrt(x); 
    printf("The square root of %lf is %lfn", x, result); 
    return 0; 
} 

此代码不起作用,因为它采用变量的平方根.如果你改变了sqrt(x),to sqrt(20.0),代码工作正常,为什么？请解释.

另外,我如何获得变量的平方根(这是我真正需要的)？

OUTPUT:

matthewmpp@annrogers:~/Programming/C.progs/Personal$ vim sqroot1.c
matthewmpp@annrogers:~/Programming/C.progs/Personal$ cc -c sqroot1.c
matthewmpp@annrogers:~/Programming/C.progs/Personal$ cc -o sqroot1 sqroot1.c
matthewmpp@annrogers:~/Programming/C.progs/Personal$ ./sqroot1
4.472136
matthewmpp@annrogers:~/Programming/C.progs/Personal$ vim sqroot2.c
matthewmpp@annrogers:~/Programming/C.progs/Personal$ cc -c sqroot2.c
matthewmpp@annrogers:~/Programming/C.progs/Personal$ cc -o sqroot2 sqroot2.c
/tmp/ccw2dVdc.o: In function `main':
sqroot2.c:(.text+0x29): undefined reference to `sqrt'
collect2: ld returned 1 exit status
matthewmpp@annrogers:~/Programming/C.progs/Personal$ 

注意:sqroot1是20.0的sqroot.sqroot2是变量的sqroot.

matthewmpp@annrogers:~/Programming/C.progs/Personal$ cc …

matthewmpp@annrogers:~/Programming/C.progs/Personal$ cat prime4.c
/*
 * File:   main.c
 * Author: matthewmpp
 *
 * Created on November 7, 2010, 2:16 PM
 */

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

/*
prime numbers.
version4
should tell whether a number is prime or not prime.
by using other prime numbers.
 */

int input_func ()
{
    char line[100];
    int n_input;

    while (1) {
        printf("Please enter a whole number.\n");
        fgets(line, sizeof (line), stdin);
        sscanf(line, "%d", &n_input);

        if (n_input >= 0)
            break;

        return (n_input);
    }
} …

/*\n * File:   main.c\n * Author: matthewmpp\n *\n * Created on November 7, 2010, 2:16 PM\n */\n\n#include <stdio.h>\n#include <string.h>\n#include <stdlib.h>\n#include <math.h>\n\n/*\nprime numbers.\nversion4\nshould tell whether a number is prime or not prime.\nby using other prime numbers.\n */\n\nint input_func() {\n    char line[100];\n    int n_input;\n\n    while (1) {\n        printf("Please enter a whole number.\\n");\n        fgets(line, sizeof (line), stdin);\n        sscanf(line, "%d", &n_input);\n\n        if (n_input >= 0)\n            break;\n\n        return (n_input);\n    }\n}\n\nint ifstatements_func(n_ifstate)\nint n_ifstate;\n{\n    if (n_ifstate == 0) {\n        printf("The number, %d, is not prime and has …