Why did this code do not make error, if input would be Smith like "4.5"? How to solve the problem

Question

https://code.sololearn.com/c74YEq2GN8QZ/?ref=app

Answer 1

%d stands for decimal and it expects an argument of type int.
Floating-point types float and double both of them use %f.
In C99 you can also use %lf to signify the larger size of double.

float a;
scanf("%f", &a);
printf("Hello, %.1f\n", a);

Answer 2

I mean, the program should work with integer only, and if user would input float — it needs to return error.

Answer 3

Here is a way to do it with all integers:

#include <stdio.h>

int main() {
int a, b=-1;
scanf("%d.%d", &a, &b);
if (b>=0)
puts("Invalid input");
else
printf("Hello, %d\n", a);
return 0;
}

Use scanf to detect the decimal point and place the decimal portion into b. If b is changed from its initialized value of -1 then you can tell that it was floating point input.

Answer 4

// Hope this code helps you

https://code.sololearn.com/c6hJ3kE5mMxN

char sn[10];
fgets (sn, sizeof(sn), stdin);

int na=0;
for (int i=0; i<strlen(sn); i++) {
if ( !isdigit(sn[i]) ) { na++; break; }
}
if (na>0) puts("Invalid Input, n should be integer number"); else printf("%d", atoi(sn) );

Answer 5

Thanks. :)
We have a task to use only 'stdio' library, and have a deadline with one day only. So finally we got something like that (but I do not understand, why it always give me invalid output there).
https://code.sololearn.com/ch5utWF8ULP5/?ref=app