How to call a contract function from another contract ?

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S O L I D I T Y
F U N C T I O N C A L L S

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How we can do ?
How a function in
another contract can
be called ?

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Function Calls
There are mainly three ways to call function between contracts.
contractA = contractA(address)
contractA = new contractA()
require(_add.call(bytes4(keccak256("f(datatype)")),value));

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Function Calls
contractA = new contractA()
pragma solidity ^ 0.4.20;
contract member{
uint age;
function setAge(uint _age){ age=_age; }
function getAge() public returns(uint){ return age; }
}
contract teacher{
function set() public{
member m=new member();
m.setAge(12);
}
}

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Function Calls
contractA = contractA(address)
pragma solidity ^ 0.4.20;
contract member{
uint age;
function setAge(uint _age){ age=_age; }
function getAge() public returns(uint){ return age; }
}
contract teacher{
function set(address _add) public{
member m1=member(_add);
m1.setAge(14);
}
}

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Function Calls
require(_add.call(bytes4(keccak256("f(datatype)")),value));
pragma solidity ^ 0.4.20;
contract member{
uint age;
function setAge(uint _age){ age=_age; }
function getAge() public returns(uint){ return age; }
}
contract teacher{
function set(address _add)public{
require(_add.call(bytes4(keccak256("setAge(uint256)")),12));
}
}