c - Why am I getting a Segmentation Fault in function search_lastname? -

the following program accepts data user of student name , last name , score. function search_lastname supposed search records of given last name. gives segmentation fault. other function print records , cases switch have been created further functions yet added program .

#include<stdio.h> #include<string.h> #include<stdlib.h> char **first_name, **last_name; float *score; int entry; void print(); void search_lastname(char search_last_name[21]); int main() { int i,option; char search_last_name[21];     {     printf("\nplease indicate number of records want enter (the minimum number of entries 5) :");                          scanf("%d",&entry);     } while(entry<=4); score=(float*)malloc(entry*sizeof(float)); first_name=(char**)malloc(entry*sizeof(char*)); last_name=(char**)malloc(entry*sizeof(char*)); for(i=0;i<entry;i++)     {     first_name[i]=(char*)malloc(21*sizeof(char));     last_name[i]=(char*)malloc(21*sizeof(char));     } printf("please input records of students (enter new line after each record), following format first name last name score \n"); for(i=0;i<entry;i++)     {     scanf("%s%s%f",&first_name[i],&last_name[i],&score[i]);                                                             /*input of records itself*/     } {     printf("\nplease choose appropriate options :");                                                /*switch statement choosing options.*/     printf("\nprint records (press 1)\nadd new record (press 2)\ndelete records (press 3)\nsearch last name (press 4)\nsort score (press 5)\nsort last name (press 6)\nfind median score (press 7)\nexit program (press 0)");     scanf("%d",&option);     switch(option)         {         case 1  :print();             break;         case 2  :             break;         case 3  :             break;         case 4  :             printf("\n please enter last name want search: ");             scanf("%s",search_last_name);             search_lastname(search_last_name);             break;         case 5  :             break;         case 6  :             break;         case 7  :             break;         case 0  :             break;         default :              printf("\n please enter valid option.");         } } while(option>=1 && option<=7); return 0; }  void print() { int i; printf("\n records of students follows :"); for(i=0;i<entry;i++)     {     printf("\nfirst name:%s, last name:%s, score:%f\n",&first_name[i],&last_name[i],score[i]);     } }   void search_lastname(char search_last_name[21])                                     /*funtion search last name*/   { int i,counter=0; for(i=0;i<entry;i++)     {     if(strcmp(search_last_name,last_name[i])==0)         {         printf("\nfirst name:%s, last name:%s, score:%f\n",first_name[i],last_name[i],score[i]);         }     }  } 

your problem usage of scanf() function. need change

scanf("%s%s%f",&first_name[i],&last_name[i],&score[i]); 

to

scanf("%20s %20s %f", first_name[i], last_name[i], &score[i]); 

without length modifier, %s specifier won't able seperate input strings , over-writing memory area past allocated memory, causing undefined behavior.

also, it's recommended check return value of scanf() ensure proper input.

note:

1. the recommended signature of main() int main(void).
2. do not cast return value of malloc() , family.