Input Validation in Depth

Input Validation, Robustness

Robust programs validate input everywhere: scanf return, range, buffer size.

Validate scanf results

int result = scanf("%d", &num) == 1;
if (result == 0) {
    printf("Invalid input.");
}

Clear the buffer after failure

while (getchar() != '\n');

Flushes the bad characters.

Read to the line with a size limit

fgets(line, sizeof(line), stdin);

safe against overruns.

Final shape

1. Get data.
2. Check the get was successful.
3. Validate range/type.
4. Else, clear and ask again.

TL;DR

• Check scanf's return value.
• Clear leftover input after a failed read.
• Use fgets + size to cap reads.
• Loop until input is valid.