String functions for C college assignments

strings.c

#include <stdio.h>
#include <stdlib.h>

/* read string from stdin */
char* readString(char end) {
	char* string = NULL;
	char value = '@';
	int counter = 0;

	while (value != end) {
		scanf("%c", &value);
		string = (char*)realloc(string, sizeof(char) * counter + 1);
		string[counter] = value;
		counter++;
	}

	string[counter-1] = '\0';
	return string;
}

/* read string from file */
char* readfString(FILE* fp, char end) {
	char* string = NULL;
	char value = '@';
	int counter = 0;

	while (value != end) {
		fscanf(fp, "%c", &value);
		string = (char*)realloc(string, sizeof(char) * counter + 1);
		string[counter] = value;
		counter++;
	}

	string[counter-1] = '\0';
	return string;
}