学校でC言語の基礎学んだから見て ID:DbdPNFS7

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

int main() {

char* input = malloc(sizeof(char));
if (input == NULL){
perror("ERROR: input memory allocation failed.");
exit(EXIT_FAILURE);
}

int ch = 0;

int i = 0;

printf("Please give an integer: ");

while ((ch = getchar()) != EOF && ch != '\n'){
input = realloc(input, (size_t)(i+1) * sizeof(char));
if (input == NULL){
perror("ERROR: input memory allocation failed.");
exit(EXIT_FAILURE);
}
if (ch < 48 || ch > 57){
free(input);
fprintf(stderr, "ERROR: Please give a valid integer.\n");
exit(EXIT_FAILURE);
}
input[i] = ch;
i++;
}

input[i] = '\0';

printf("Given integer is: %s\n", input);

free(input);

return 0;
}