Something

 #include <stdio.h> 
 #define MAXLINE 1000    /* maximum input line size */ 
 int max;                /* maximum length seen so far */ 
 char line[MAXLINE];     /* current input line */ 
 char longest[MAXLINE];  /* longest line saved here */ 
 int getline(void); 
 void copy(void); 
 /* print longest input line; specialized version */ 
 main() 
 { 
     int len; 
     extern int max; 
     extern char longest[]; 
     max = 0; 
     while ((len = getline()) > 0) 
         if (len > max) { 
             max = len; 
             copy(); 
         } 
     if (max > 0)  /* there was a line */ 
         printf("%s", longest); 
     return 0; 
 } 
 /* getline:  specialized version */ 
 int getline(void) 
 { 
     int c, i; 
     extern char line[]; 
     for (i = 0; i < MAXLINE - 1 
          && (c=getchar)) != EOF && c != '\n';
              line[i] = c; 
     if (c == '\n') { 
         line[i] = c; 
         ++i; 
     } 
     line[i] = '\0'; 
     return i; 
 } 
 /* copy: specialized version */ 
 void copy(void) 
 { 
     int i; 
     extern char line[], longest[]; 
     i = 0; 
     while ((longest[i] = line[i]) != '\0') 
         ++i; 
 }