Compilare: user.c: In function ‘main’: user.c:10:5: warning: implicit declaration of function ‘strlen’ [-Wimplicit-function-declaration] while(i!=(strlen(s)+2)) ^ user.c:10:15: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] while(i!=(strlen(s)+2)) ^ user.c:22:16: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] {for(i=0;i<strlen(s);i++) {{if(s[i]==':') {i+=2;while(!((s[i]>='a'&&s[i]<='z')||(s[i]>='A'&&s[i]<='Z')||(s[i]>='0'&&s[i]<='9')))i++; ^ user.c:9:10: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result] fgets(s,100,f); ^ user.c:13:9: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result] fgets(s,100,f); ^ user.c:18:10: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result] fgets(s,100,f); ^ user.c:28:10: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result] fgets(s,100,f); ^ user.c:10:12: warning: ‘i’ may be used uninitialized in this function [-Wmaybe-uninitialized] while(i!=(strlen(s)+2)) ^