Linear search means that you go through all the elements in the array in order until you find the element you search for, or reach the end of the array.
int num; //Your number, random
int array[100]; //Suppose it's random
bool bSuccess = false;
for(int i = 0;i < 100;i++)
if(num == array[i]){bSuccess = true;[...]} //Found !
if(!bSuccess){[...]} //Could not find the value