A.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Tiny Server</title>
</head>
<body>
<form action="/cgi-bin/form-adder" method="GET">
<p>first number: <input type="text" name="first"/></p>
<p>second number: <input type="text" name="second"/></p>
<input type="submit" value="Submit"/>
</form>
</body>
</html>
browser should visit localhost:5000/cgi-bin/form-adder?first=222&second=333
B.
form-adder handle query string like first=ddd&second=dddd
/*
* form-adder.c - a minimal CGI program that adds two numbers together
*/
#include "../csapp.h"
int main(void) {
char *buf, *p;
char arg1[MAXLINE], arg2[MAXLINE], content[MAXLINE];
int n1=0, n2=0;
/* Extract the two arguments */
if ((buf = getenv("QUERY_STRING")) != NULL) {
p = strchr(buf, '&');
*p = '\0';
sscanf(buf, "first=%d", &n1);
sscanf(p+1, "second=%d", &n2);
}
/* Make the response body */
sprintf(content, "Welcome to add.com: ");
sprintf(content, "%sTHE Internet addition portal.\r\n<p>", content);
sprintf(content, "%sThe answer is: %d + %d = %d\r\n<p>",
content, n1, n2, n1 + n2);
sprintf(content, "%sThanks for visiting!\r\n", content);
/* Generate the HTTP response */
printf("Connection: close\r\n");
printf("Content-length: %d\r\n", (int)strlen(content));
printf("Content-type: text/html\r\n\r\n");
printf("%s", content);
fflush(stdout);
exit(0);
}