C - How to check if unwanted character is in an array? - c

Question

I have a question about string arrays.
I am trying to find a way to check if a string has an undesired character in it.
Tested array has to only contain one of these 8 options: {'A','a','C','c','G','g','T','t'}
All the white spaces are removed prior to this checking process.
If I have two arrays
A = {AGctcgtacgtacg}
B = {CGTAagctFcg}
A should pass the test and B should fail because it has 'F' in it.
I'm thinking of using a for loop to go over each element of the array and trying to check if the character is one of the options.
const char test[] = {'A','a','C','c','G','g','T','t'};
int l = strlen(A);
char A[] = {AGctcgtacgtacg}
char B[] = {CGTAagctFcg}
for (i = 0; i < l; i++){
if (A[i] is one of the characters in test){
do nothing... (keep checking)
}
else{
break;
printf("Error: the array contains unwanted character.");
exit(1);
}
}

Answer 1

You can use standard C function strspn declared in header <string.h> to check whether a string contains only valid characters.
For example
#include <stdio.h>
#include <string.h>
int main( void )
{
const char *test = "AaCcGgTt";
char A[] = "AGctcgtacgtacg";
char B[] = "CGTAagctFcg";
if (A[strspn(A, test)] == '\0')
{
puts("Array A has valid characters");
}
else
{
puts("Array A has invalid characters");
}
if (B[strspn(B, test)] == '\0')
{
puts("Array B has valid characters");
}
else
{
puts("Array B has invalid characters");
}
}
The program output is
Array A has valid characters
Array B has invalid characters
If you need to know also the position of the first invalid character then you can write for example
#include <stdio.h>
#include <string.h>
int main()
{
const char *test = "AaCcGgTt";
char A[] = "AGctcgtacgtacg";
char B[] = "CGTAagctFcg";
size_t n;
if (A[n = strspn(A, test)] == '\0')
{
puts("Array A has valid characters");
}
else
{
puts("Array A has invalid characters");
printf("Invalid character is %c at position %zu\n", A[n], n);
}
if (B[n = strspn(B, test)] == '\0')
{
puts("Array B has valid characters");
}
else
{
puts("Array B has invalid characters");
printf("Invalid character is %c at position %zu\n", B[n], n);
}
}
The program output is
Array A has valid characters
Array B has invalid characters
Invalid character is F at position 8

Answer 2

Try using strchr(...) NOTE that test needs to be NUL terminated
const char test[] = {'A','a','C','c','G','g','T','t','\0'};
int l = strlen(A);
char A[] = {AGctcgtacgtacg}
char B[] = {CGTAagctFcg}
for (i = 0; i < l; i++){
if (strchr(test, A[i])){
do nothing... (keep checking)
}
else{
break;
printf("Error: the array contains unwanted character.");
exit(1);
}
}