why I can't get multiple spaces in *?

Question

int main()
{

    int input;
    printf("input lenth : \n");
    scanf("%d", &input);
    while(getchar()!='\n')
        continue;
    printf("input str : \n");
    char* sentence = (char*)malloc(sizeof(char) * input);
    fgets(sentence, sizeof(sentence), stdin);
    reverse(sentence, strlen(sentence));
    free(sentence);
    return 0;
}

I learn fgets can get space.

so I malloc enough space to sentence ex) 100

and I input I am a boy

But when I print my sentence, IT just print I am a ...

what's th problem?

Answer 1

This statement

fgets(sentence, sizeof(sentence), stdin);

is incorrect. It seems you mean

fgets(sentence, input, stdin);

Otherwise sizeof( sentence ) will yield the size of a pointer declared like

char* sentence = (char*)malloc(sizeof(char) * input);

Pay attention to that the function fgets can append the new line character '\n' to the entered string. You should remove it like

sentence[ strcspn( sentence, "\n" ) ] = '\0';