c - Error during string read/write -

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• implicit declaration of 'gets' 2 answers

the following program used write string file when compile using gcc shows errors

#include<stdio.h> #include<string.h> #include <stdlib.h>  int main() {     file *fp;     char s[80];     fp = fopen("poem.txt", "w");     if(fp == null) {         puts("cannaot open file");         exit(1);     }     printf("\n enter");     while(strlen(gets(s)) > 0) {         fputs(s, fp);         fputs("\n", fp);     }     fclose(fp);     return 0; } 

the error when compiling

gcc expi.c expi.c: in function ‘main’: expi.c:18:14: warning: implicit declaration of function ‘gets’ [-wimplicit-function-declaration]  while(strlen(gets(s))>0)               ^ expi.c:18:14: warning: passing argument 1 of ‘strlen’ makes pointer integer without cast [-wint-conversion] in file included expi.c:2:0: /usr/include/string.h:394:15: note: expected ‘const char *’ argument of type ‘int’  extern size_t strlen (const char *__s)                ^ /tmp/cchmkvw7.o: in function `main': expi.c:(.text+0x87): warning: `gets' function dangerous , should not used. 

the code not compiling text book code , not being able run . creates file doesnt add runtime text it

first of all, not use gets(). it's dangerous function because there huge risk of overflowing array , also, removed recent c standard c11.

also, should understand how strlen() works , how c-strings represented. you, can same as

while (strlen(string) > 0) 

by writing

while (string[0] != '\0') 

but need understand c-string is. , should check string not null pointer in both cases.

maybe want

while (fgets(s, sizeof(s), stdin) != null) ... 

not fgets() functionality of gets() implemented in such way can safe avoiding buffer overflow.