c语言如何判断所输入字符串里面含有某些内容呢

#include<stdio.h>
int main()
{
    int i;
    boolean q = false,w = false,e = false,r = false;
    char a[100];
    printf("Enter a string: ");
    i = 0;
    while ((a[i] = getchar()) != '\n')
    {
        i++;
    }
    a[i] = '\0';
  for(int j=0; j<sizeof(a), j++) {
    if(a[j] =='D' || a[j] =='d') {
     q = true;
} else if (a[j] =='G' || a[j] =='g') {
    w = true;
} else if (a[j] =='U'|| a[j] =='u') {
    e = true;
} else if (a[j] =='T' || a[j] =='t') {
    t = true;
}
  
}
if(qwer) {
  printf("这些字母可以组成");
} else {
  printf("这些字母不可以组成");
}
return 0;
}

string.contains()