Question

How to mask a number with stars except the first 6 and the last 4 digits in C

Answer 1

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

char* maskNumberWithStarsExceptFirstSixAndLastFour(char* cardNumber) {
    int cardNumberLength = strlen(cardNumber);
    int first6DigitsLength = 6;
    int last4DigitsLength = 4;
    
    char* first6Digits = malloc(first6DigitsLength + 1);
    strncpy(first6Digits, cardNumber, first6DigitsLength);
    first6Digits[first6DigitsLength] = '\0';
    
    char* last4Digits = malloc(last4DigitsLength + 1);
    strncpy(last4Digits, cardNumber + cardNumberLength - last4DigitsLength, last4DigitsLength);
    last4Digits[last4DigitsLength] = '\0';
    
    int requiredMaskLength = cardNumberLength - first6DigitsLength - last4DigitsLength;
    char* requiredMask = malloc(requiredMaskLength + 1);
    memset(requiredMask, '*', requiredMaskLength);
    requiredMask[requiredMaskLength] = '\0';
    
    char* maskedNumber = malloc(cardNumberLength + 1);
    sprintf(maskedNumber, "%s%s%s", first6Digits, requiredMask, last4Digits);
    
    free(first6Digits);
    free(last4Digits);
    free(requiredMask);
    
    return maskedNumber;
}

int main() {
    char* cardNumber = "9003125334656789";
    
    char* maskedNumber = maskNumberWithStarsExceptFirstSixAndLastFour(cardNumber);
    
    printf("%s\n", maskedNumber);
    
    free(maskedNumber);
    
    return 0;
}



/*
run:

900312******6789

*/

 

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